Doc #95 — Electric Motor Rewinding

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RECOMMENDED ACTIONS (BY URGENCY)

First month (Phase 1)

1. Classify all motor rewind shops as critical facilities and all experienced motor rewinders as essential personnel. Prevent redeployment or closure.
2. National motor rewind shop census: Through the skills census (Doc #8), identify every motor rewind shop in NZ — location, equipment, material stocks, workforce skills and ages. Include shops that have closed recently (within 5 years) — their equipment and stocks may still exist.
3. Inventory magnet wire stocks nationally: At rewind shops, electrical wholesalers (Rexel, Ideal Electrical, Edisons), motor manufacturers’ NZ agents, and any other holders. Record by wire gauge, insulation class, and quantity. This is the strategic reserve for motor rewinding.
4. Inventory insulation materials: Slot liner materials (Nomex, Mylar, DMD composite), varnish, sleeving, and lacing tape at all rewind shops and electrical supply outlets.
5. Secure bearing stocks nationally: Identify and protect all holdings of electric motor bearings (primarily deep groove ball bearings, 6200–6300 series) at bearing distributors (CBC, Motion, NTN-SNR agents) and motor rewind shops. Bearings are the second most common cause of motor failure.⁶
6. Identify priority motors: Working with regional councils, dairy cooperatives (Fonterra regional offices), and water authorities, compile a register of motors whose failure would have the most severe consequences — town water supply pumps, dairy shed milking motors, hospital essential services, grain milling drives.

First year (Phase 1–2)

7. Begin knowledge capture from experienced rewinders. Film rewinding procedures for common motor types. Document winding data (turns, wire sizes, connection patterns) for the most common motor models in NZ’s fleet. This data is essential — without it, a failed motor cannot be correctly rewound.
8. Establish regional rewinding capability. Ensure at least one functional rewind shop exists in each NZ region (Northland, Auckland, Waikato, Bay of Plenty, Gisborne/Hawkes Bay, Taranaki, Manawatu-Wanganui, Wellington, Nelson-Marlborough, Canterbury, West Coast, Otago, Southland). Some regions may currently lack this capability.
9. Begin copper wire drawing trials for magnet wire. Working with Pacific Steel (Doc #70) and/or copper recycling operations, trial drawing copper wire to the fine gauges needed for motor winding. This does not solve the insulation problem but establishes the bare-wire supply chain.
10. Begin varnish substitution research. Test NZ-producible varnishes (shellac-based, linseed oil-based, tung oil-based) for electrical insulation properties — dielectric strength, temperature resistance, moisture resistance. This is a critical R&D priority.
11. Establish a motor data library. Collect winding data sheets for the most common motor types in NZ — ideally from original manufacturers, but failing that, from systematic recording during each rewind. Every motor that passes through a rewind shop should have its winding data recorded and centrally filed.
12. Cross-train transformer technicians and motor rewinders. Motor rewinding and transformer rewinding (Doc #70) share core skills. Cross-training expands both workforces.

Years 1–3 (Phase 2)

13. Achieve routine rewinding capacity of 2,000–5,000 motors per year nationally. This is an estimate of the annual failure rate for NZ’s most critical motor population (see Section 1.3).
14. Develop NZ-produced magnet wire. Combine copper wire drawing (Doc #70) with a locally produced enamel insulation coating — the most challenging step.
15. Develop NZ-produced slot insulation from locally available materials (see Section 5).
16. Develop NZ-produced impregnation varnish from domestic resin sources (see Section 5).
17. Standardise motor designs for the most common applications (dairy, water pumping, grain milling) to reduce the variety of parts and winding configurations.

Years 3–7 (Phase 3)

18. Scale domestic magnet wire production to meet ongoing rewinding demand.
19. Begin new motor manufacture for standardised designs — initially assembling NZ-wound stators with imported (stockpiled) rotors, bearings, and frames.
20. Develop rotor casting capability — squirrel-cage rotors require aluminium die casting (Doc #93). This is a significant step toward full motor manufacture.
21. Assess feasibility of electrical steel lamination production at NZ Steel (Doc #89) for motor stator and rotor cores.

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ECONOMIC JUSTIFICATION

The value of motors to NZ’s recovery

Electric motors convert NZ’s abundant renewable electricity into mechanical work. Without motors, electricity is limited to heating and lighting. With motors, it drives the entire productive economy: agriculture, manufacturing, water supply, food processing, transport infrastructure. The economic value of maintaining NZ’s motor fleet is difficult to overstate — it is the difference between an electrified economy and a manual-labour economy.

Investment required

Rewinding program (sustaining existing capability):

• Facilities: Existing rewind shops — no new construction needed, though capacity expansion and regional coverage gaps require investment.
• Equipment: Existing winding equipment at rewind shops. Additional winding lathes and test equipment can be fabricated (Doc #91) or redistributed from closed shops.
• Training: 50–100 new rewinders trained over 3 years, from the existing pool of electricians and electrical trade workers. Training period: 6–12 months under experienced supervision.
• Materials: From existing stocks initially, transitioning to NZ-produced materials over 2–5 years.
• Estimated labour: 5–10 person-years to establish expanded and regionally distributed capability, plus 50–100 person-years per year of ongoing rewinding production at 2,000–5,000 motors per year (a single motor rewind takes 4–40 person-hours depending on motor size).⁷

Material supply chain development (magnet wire and insulation):

• Copper wire drawing to magnet wire gauges: 5–10 person-years of development, building on existing wire drawing capability (Doc #70).
• Enamel insulation for magnet wire: 10–20 person-years of R&D and pilot production — this is the most uncertain element.
• Varnish production: 3–5 person-years of development using NZ resin sources.
• Total material supply chain: approximately 20–35 person-years of development spread over 3–7 years.

Comparison with the alternative

The alternative to motor rewinding is accepting that every failed motor is permanently lost. At an estimated failure rate of 2–5% per year for the active motor fleet, NZ loses thousands of motors annually. Within a decade, critical systems — water supply pumps, milking machines, grain mills, machine tools — begin failing without replacement. The consequence is progressive loss of mechanised capability across the entire economy.

A single rewound dairy shed motor, keeping a milking operation functional for another 10–15 years, justifies substantial rewinding labour investment relative to the productive output preserved. At a rewinding cost of 8–16 person-hours (Section 3.3) and a motor life extension of 10–15 years for a dairy operation producing milk for a community, the economic case for motor rewinding is strong — stronger, in most cases, than the investment case for most other recovery program activities of similar cost. A formal cost-benefit analysis would strengthen this claim, but is deferred pending better data on motor failure rates and rewinding throughput from Year 1 operations.⁸

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1. NZ’S ELECTRIC MOTOR POPULATION

1.1 Types and distribution

NZ’s electric motor fleet consists primarily of three-phase and single-phase AC induction motors:⁹

Three-phase induction motors (industrial and agricultural):

• Dairy shed motors (2.2–15 kW): NZ has approximately 10,500–11,000 dairy herds,¹⁰ each requiring motors for milking machines (vacuum pumps, milk pumps), refrigeration compressors, water pumps, and effluent handling. A typical dairy shed contains 3–8 motors. Estimated total: 40,000–80,000 dairy motors. These are among the highest-priority motors in the country — dairy is NZ’s largest agricultural export sector by value and a primary source of fat and protein for the population, alongside beef, lamb, and fish.¹¹
• Water supply pumps (1.5–200 kW): Municipal water supply, irrigation, and stock water pumping. NZ’s approximately 67 territorial authorities operate water supply systems with multiple pump stations each.¹² Estimated thousands of pump motors nationally — each one directly supplying drinking water or irrigation to a community.
• Food processing motors (0.75–500 kW): Meat processing, dairy manufacturing (Fonterra plants and others), grain milling, fruit and vegetable processing. These motors drive the food supply chain.
• Machine tool motors (0.75–15 kW): Every lathe, mill, drill, and grinder in NZ’s machine shops (Doc #91) is driven by an electric motor. Machine shop capability depends on motor availability.
• Forestry and sawmill motors (5–200 kW): Sawmills, wood processing, and associated equipment.
• General industrial (0.37–500 kW): Compressors, fans, conveyors, pumps, and drives across all industrial sectors.

Single-phase motors (domestic and light commercial):

• Domestic appliances: Washing machines, refrigerators, freezers, fans, power tools. Estimated millions of single-phase motors in NZ households. Individually of lower priority than industrial motors, but domestic refrigeration and water pumping are important for household food security and health.
• Farm workshop equipment: Bench grinders, small lathes, drill presses, air compressors. Single-phase motors serving agricultural workshops in areas without three-phase supply.
• Small commercial: Restaurant equipment, small pumps, ventilation fans.

1.2 Common motor sizes in NZ

NZ uses IEC standard motor frame sizes (metric). The most common sizes in industrial and agricultural service:¹³

Application	Typical power range	Common frame sizes	Typical quantity in NZ
Dairy vacuum pump	4–11 kW	112M–160M	10,000–15,000
Dairy milk pump	1.5–4 kW	90S–112M	10,000–15,000
Water supply pump	2.2–75 kW	100L–280M	5,000–15,000
Machine tool drive	1.5–7.5 kW	90S–132M	10,000–30,000
Refrigeration compressor	2.2–30 kW	100L–200L	10,000–30,000
Grain mill / feed mixer	4–37 kW	112M–225M	2,000–5,000
Sawmill main drive	15–200 kW	160M–315L	1,000–3,000

Honest assessment: These quantity estimates are rough, based on the number of relevant facilities in NZ and typical motor counts per facility. The actual national motor fleet has never been counted. The skills census (Doc #8) should capture motor populations at critical facilities.

1.3 Annual failure rate

Well-maintained industrial motors have an annual failure rate of approximately 2–5%, depending on operating environment, loading, and maintenance quality.¹⁴ Under post-event conditions — potentially less rigorous maintenance, more frequent starts and stops, operation in adverse conditions — failure rates may be higher.

For NZ’s most critical motor population (estimated at 100,000–200,000 industrial and agricultural motors), this implies 2,000–10,000 motor failures per year requiring either rewinding or replacement. At the lower end, this is manageable with existing rewinding capacity. At the upper end, it requires significant expansion of capability and careful triage of which motors get rewound first.

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2. MOTOR FAILURE MODES

2.1 Why motors fail

The three primary failure modes for induction motors are, in order of frequency:¹⁵

Bearing failure (approximately 40–50% of motor failures):

Ball bearings in the motor endplates support the rotor. They fail due to lubrication degradation, contamination (dust, moisture), overloading, misalignment, or electrical discharge (shaft currents, which can pit bearing races). Bearing failure is typically progressive — increasing noise and vibration precede seizure.

Bearing replacement does not require rewinding — it requires the correct replacement bearing (matched by bore diameter, outer diameter, and width to the original), a bearing puller, a press or sleeve for installation, and the skill to disassemble and reassemble the motor without damaging endplates or shaft shoulders. For an experienced fitter with the correct bearing in stock, this is a well-defined repair taking 1–4 hours depending on motor size. The binding constraint is bearing availability — NZ imports all bearings (see Section 5.5).

Stator winding failure (approximately 30–40% of motor failures):

The stator winding — coils of insulated copper wire wound into slots in the stator core — degrades over time as insulation ages. Heat is the primary aging agent: every 10°C increase in winding temperature roughly halves insulation life (the Arrhenius relationship, well established for motor insulation).¹⁶ Moisture, chemical contamination, mechanical vibration, and voltage spikes (from variable-speed drives, switching, or lightning) also degrade insulation.

When insulation fails, adjacent turns or adjacent coils short-circuit. The shorted turns carry excessive current, generate heat, and progressively damage surrounding insulation — a cascading failure that, if not caught quickly, destroys the entire winding. A motor with a failed stator winding must be rewound.

Rotor failure (approximately 5–10% of motor failures):

In squirrel-cage induction motors (the vast majority of industrial motors), the rotor has aluminium or copper bars cast or inserted into slots in the rotor core, connected at each end by a shorting ring. Rotor failures include broken bars, cracked end rings, and rotor core damage. Rotor repair is more difficult than stator rewinding — it may require recasting the rotor bars (aluminium die casting capability, Doc #93) or in some cases is impractical, requiring the rotor to be sourced from a similar scrapped motor.

Other failures: Shaft damage, frame cracking, terminal box damage, cooling fan breakage. These are typically repairable with general machining (Doc #91) and fabrication capability.

2.2 Diagnosis

Before a motor is rewound, the failure mode must be correctly identified. Rewinding a motor with a bearing failure is wasteful; replacing bearings on a motor with a winding failure is ineffective.

Basic diagnostic tests:

• Visual inspection: Discoloured or burned insulation is visible once the motor is opened. Smoke staining, melted varnish, and copper discolouration indicate winding failure. Scoring, pitting, or discolouration on bearing surfaces indicates bearing failure.
• Insulation resistance test (megger test): Apply 500V or 1,000V DC between the winding and the motor frame using an insulation tester. A healthy motor winding shows insulation resistance of at least 1 megohm per kV of rated voltage plus 1 megohm (the “1 megohm per kV + 1” rule of thumb). Values below 1 megohm total generally indicate insulation degradation requiring rewinding.¹⁷
• Winding resistance test: Measure resistance of each phase winding with a milliohmmeter or Wheatstone bridge. Phase resistances should be balanced within 1–2%. Significant imbalance indicates shorted turns or an open circuit in one phase.
• Surge comparison test: A specialised test that applies a high-voltage impulse to each phase winding and compares the response waveforms. Differences between phases indicate turn-to-turn faults. This requires a surge tester — a piece of equipment found in well-equipped rewind shops. It is the most sensitive test for detecting early winding faults.¹⁸
• Bearing assessment: Check for roughness by rotating the shaft by hand. Listen for grinding or clicking. Measure shaft endplay with a dial indicator. These simple checks identify most bearing problems.
• Growler test (rotor check): A growler is an electromagnetic device that energises the rotor and, combined with a thin steel blade or hacksaw blade held near the rotor surface, detects broken bars by the vibration pattern. This is a traditional test used in rewind shops and requires a growler — an electromagnetic core wound with a mains-voltage coil, which can be fabricated in a machine shop (Doc #91) given lamination steel for the core, magnet wire for the coil, and basic metalwork capability.¹⁹

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3. REWINDING PROCEDURES

3.1 Overview

Rewinding a stator involves removing the damaged copper windings, cleaning the stator core, installing new coils of copper magnet wire, and impregnating the completed winding with insulating varnish. The process is well-established — NZ’s rewind shops have been doing this for decades, and the procedures are documented in standard motor repair references.²⁰

3.2 Step-by-step procedure

1. Data recording (before any disassembly):

Record all winding data from the existing motor: nameplate data (power, voltage, speed, current, frame size, insulation class), connection pattern (star or delta, number of leads), number of coils per phase, coil pitch (the number of slots each coil spans), number of turns per coil, wire gauge and number of parallel strands, slot liner material and thickness, coil grouping arrangement. This data determines how the replacement winding is fabricated. If the winding data is not recorded before the old winding is removed, the motor may be impossible to rewind correctly.

This is the single most common cause of rewinding failure in practice — failure to record data before stripping the old winding. Rewind shops should maintain a data library of winding specifications for all motor types they have encountered.

2. Burnout or chemical stripping:

The old winding must be removed from the stator core. Two methods:

• Burnout oven: The stator is heated to approximately 350–400°C in a controlled-atmosphere oven. This chars the insulation (enamel, varnish, slot liners) to a brittle residue that can then be scraped and brushed out of the stator slots — a labour-intensive step requiring care to avoid damaging slot teeth. The temperature must be carefully controlled — exceeding approximately 400°C risks damaging the stator core’s interlaminar insulation, which would increase core losses and reduce motor efficiency permanently.²¹ A burnout oven can be constructed from firebrick (available from demolished industrial kilns, pizza ovens, or NZ-produced from refractory clay), electric heating elements (salvaged from domestic ovens or wound from nichrome resistance wire), and a thermocouple with a temperature controller or careful manual monitoring using a pyrometer.
• Chemical stripping: Soak the stator in a solvent that dissolves the varnish and enamel. Methylene chloride (dichloromethane) was traditionally used but is toxic and increasingly restricted. NZ-available alternatives are limited. Chemical stripping is slower but avoids the risk of core damage from overheating.

3. Core cleaning and inspection:

After burnout, remove all copper and residual insulation from the stator slots. Clean with compressed air and brushes. Inspect the core for damage: burned spots (dark discolouration indicating shorted laminations), mechanical damage (bent or splayed slot teeth from improper winding removal), and corrosion.

Test core losses: energise the core (without windings) at rated flux density using a test winding and measure the power drawn. Compare to expected core loss for the motor frame size. Excessive core loss indicates damaged interlaminar insulation — a core that has been overheated during burnout or burned through in a winding failure. Mild damage can sometimes be tolerated (the motor runs slightly hotter). Severe damage may require replacing the stator core — which effectively means the motor frame becomes scrap and a new core must be sourced from another motor of the same frame size.²²

4. Slot insulation:

Install slot liners — thin sheets of insulating material that line each slot in the stator core, separating the copper winding from the grounded steel core. Standard materials are Nomex (aramid paper, Class H — rated to 180°C), Mylar (polyester film, Class B — 130°C), or DMD composite (Dacron-Mylar-Dacron laminate). These are all imported.

NZ substitutes (see Section 5.3) include shellac-impregnated paper or rag paper, and potentially NZ-produced fish paper (vulcanised cellulose fibre). These substitutes have lower temperature ratings — approximately Class A (105°C) or Class E (120°C) — meaning the motor must be derated (operated at lower power) to avoid overheating the insulation. This is a real performance gap, not a minor inconvenience: a motor rewound with Class A insulation may need to be derated to 60–75% of its original rating to maintain adequate insulation life.²³

5. Coil winding:

Wind the new coils. Methods depend on shop equipment:

• Hand winding: Coils wound by hand on a wooden or metal form shaped to the correct slot pitch and coil dimensions, then inserted into the stator slots. This is the traditional method and requires no specialised machinery — only a form (which must be dimensioned to match the specific stator), a supply of magnet wire, and a skilled rewinder. Hand winding is slower (roughly twice the labour of machine winding) but feasible for any motor size.
• Winding machine (coil winding lathe): A rotating mandrel with a turns counter, driven by hand crank or electric motor. The rewinder guides the wire onto the form while the machine counts turns and maintains tension. Significantly faster and more consistent than pure hand winding. Most NZ rewind shops have winding machines.

Coils must have the correct number of turns, wire gauge, and physical dimensions to fit the stator slots with proper clearance. If the wire gauge is not available, the rewinder can substitute an adjacent gauge — slightly larger wire means fewer turns fit, so the winding may need fewer turns (reducing voltage) or a modified winding pattern. This is an engineering judgment that experienced rewinders make routinely.

6. Coil insertion:

Insert the wound coils into the stator slots. For small motors (up to approximately 30 kW), coils are typically inserted by hand, one coil side at a time, using a fibre or wooden drift to push wire down into the slot without damaging insulation. For larger motors, automated coil insertion equipment exists but is not essential.

Install phase separators (insulating sheets between phase groups) and close the slots with slot wedges (thin strips of insulating material or fibre that hold the coils in place within the slots).

7. Connection and lacing:

Connect the coil groups according to the winding diagram — star or delta connection, correct phase sequence, correct number of parallel paths. Braze or solder the connections (silver solder or brass brazing — both feasible with NZ materials). Insulate all connections with sleeving and tape.

Lace the end windings (the portions of the coils that extend beyond the stator core at each end) with lacing cord or fibreglass tape to secure them mechanically. This prevents coil movement under the electromagnetic forces during motor operation, which can cause insulation wear and premature failure.

8. Varnish impregnation:

The completed winding is impregnated with insulating varnish, which fills air spaces within the winding, bonds the turns together, improves thermal conductivity (allowing heat to transfer from copper to core), and provides additional electrical insulation and moisture protection. Methods:

• Dip and bake: The most common method in NZ rewind shops. The wound stator is preheated (to approximately 80–100°C to drive off moisture), then dipped into a tank of varnish (a solvent-based or water-based polyester or epoxy resin), drained, and baked in an oven at approximately 130–180°C for 4–12 hours to cure the varnish. The cycle may be repeated once or twice for full penetration.²⁴
• Trickle impregnation (VPI — vacuum pressure impregnation for large motors): The stator is placed in a vacuum chamber, air is evacuated from the winding, and varnish is introduced under pressure. This achieves more complete penetration than dipping. VPI equipment exists at some NZ rewind shops and motor manufacturers — it is a strategic asset.
• Brush application: For field repairs where oven curing is not available, varnish can be brushed onto the winding and air-dried or heat-cured with portable heating equipment. Less effective than dipping but provides some insulation improvement.

9. Assembly and testing:

Reinstall the rotor, endplates, bearings, cooling fan, and terminal box. Perform final tests (Section 4).

3.3 Time and skill requirements

A complete rewind of a typical dairy shed motor (5.5 kW, frame 132) takes an experienced rewinder approximately 8–16 hours from disassembly to testing. Larger motors take proportionally longer — a 75 kW motor may require 30–60 hours. Small motors (under 2 kW) take 4–8 hours.²⁵

The skill is developed through apprenticeship. A new worker with basic electrical trade background can perform supervised rewinding after 3–6 months of training. Independent competence on standard motor types takes 1–2 years. Proficiency on the full range of motor types and the ability to handle non-standard configurations takes 3–5 years.

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4. TESTING PROCEDURES

Every rewound motor must be tested before return to service. A motor that passes these tests can be expected to perform reliably; one that fails any test should be investigated before energising under load.

4.1 Standard tests

Insulation resistance (megger test): Apply 500V DC (for motors rated up to 1,000V) between winding and frame. Minimum acceptable: 5 megohms for a new or rewound winding at 40°C (higher values expected — typically 50–500+ megohms for a freshly varnished winding).²⁶ This test verifies that the insulation system is intact. It requires only a megger (insulation resistance tester) — a robust, hand-cranked instrument widely available in NZ.

Winding resistance: Measure DC resistance of each phase using a milliohmmeter or Wheatstone bridge. Phase resistances must balance within 1–2%. This verifies correct winding and connection.

High-potential (Hi-pot) test: Apply AC voltage at 2x rated voltage plus 1,000V between winding and frame for 60 seconds. For a 400V motor, this means applying 1,800V AC. No breakdown should occur. This tests the insulation’s ability to withstand voltage stress. Requires a high-voltage test set — found in rewind shops and electrical testing laboratories.

Surge comparison test: As described in Section 2.2. Verifies turn-to-turn insulation integrity.

No-load run test: Energise the motor at rated voltage with no mechanical load. Measure no-load current (should be approximately 30–50% of rated full-load current for most induction motors), check for abnormal vibration or noise, verify correct rotation direction, and measure bearing temperature after 30–60 minutes of running. This is the final check before returning the motor to service.

4.2 Testing without commercial instruments

If commercial test equipment becomes unavailable, basic testing can be improvised:

• Insulation resistance: A megger is essential and cannot be easily replaced. However, meggers are robust, mechanically simple instruments and NZ has thousands in service across the electrical trade. Maintaining and preserving existing meggers is a high priority.
• Winding resistance: A Wheatstone bridge can be constructed from precision resistors and a galvanometer — both within NZ’s manufacturing capability (Doc #69 discusses basic instrumentation).
• Hi-pot test: Can be performed using a small step-up transformer (any transformer with the correct turns ratio, even a rewound distribution transformer — Doc #69 — with appropriate output taps).
• No-load run: Requires only a power supply, an ammeter, and the motor. The ammeter is the critical instrument — it can be an analogue moving-iron type, which is robust and has been manufactured for over a century.

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5. MATERIALS: SUPPLY, DEPLETION, AND NZ SUBSTITUTES

5.1 Copper magnet wire

Magnet wire is copper wire coated with a thin layer of enamel insulation (typically polyester, polyester-imide, or polyamide-imide). The enamel provides turn-to-turn electrical insulation in a very thin layer — approximately 0.03–0.10 mm per side, depending on wire gauge and insulation class.²⁷ This thin insulation is what allows many turns of wire to fit into a compact stator slot.

NZ does not manufacture magnet wire. The existing national stock (at rewind shops, electrical distributors, and motor manufacturers’ agents) is the entire supply. A rough estimate of 100–500 tonnes is based on typical rewind shop inventories multiplied by the number of shops, plus distributor holdings.²⁸

Depletion timeline: A typical 5.5 kW motor rewind requires approximately 3–5 kg of magnet wire. At 2,000–5,000 rewinds per year, annual magnet wire consumption would be approximately 10–25 tonnes. Existing stocks could therefore last 4–20 years, depending on initial stock size and consumption rate — a wide range reflecting the uncertainty in both numbers.

NZ production pathway:

The copper wire itself can be drawn from recycled copper (recovered from old motor windings, demolished buildings, electrical cable, plumbing) using the wire drawing process described in Doc #70. Drawing copper wire to the fine gauges needed for motor winding (0.3–5 mm diameter) requires precision dies but is feasible with tool steel dies and careful process control.

The enamel insulation is the hard problem. Commercial enamel coatings are applied as a liquid polymer dissolved in solvent, which is passed through a coating die onto the wire and then cured in a long vertical oven (a “magnet wire tower” typically 10–30 m tall) at temperatures of 400–600°C. The wire passes through multiple coating and curing cycles to build up the required insulation thickness.²⁹ The polymer chemistries (polyester-imide, polyamide-imide) require precursor chemicals that NZ does not produce.

NZ substitute enamel options (all involve performance trade-offs):

• Shellac: A natural resin (insect secretion, historically the standard electrical insulation before synthetic polymers). Shellac provides adequate insulation at temperatures up to approximately 90–100°C (Class A). NZ does not produce shellac — it comes from India and Thailand — but existing stocks may be available at paint and wood-finishing suppliers, and it could potentially be imported via sail trade.³⁰ Shellac-coated wire would limit motors to Class A temperature ratings.
• Linseed oil (raw or boiled): A drying oil produced from flax seeds (Linum usitatissimum — not harakeke). NZ grows some linseed. Oxidised (polymerised) linseed oil provides reasonable electrical insulation when baked and has been used as wire insulation historically. Temperature rating: approximately Class A (105°C). Performance is inferior to modern enamels but functional.³¹
• Tung oil: A superior drying oil with better moisture resistance than linseed. Tung trees (Vernicia fordii) were planted in NZ (primarily Northland) for oil production and some trees remain. Tung oil varnish, baked to full cure, provides Class A insulation.³²
• Cotton or fibreglass serving: Wrapping wire with a thin layer of cotton thread or fibreglass yarn, then impregnating with varnish. This was standard practice before enamel coatings became dominant (pre-1940s motors used cotton-served wire). Cotton serving adds more thickness than enamel — meaning fewer turns fit per slot — but it provides reliable insulation when properly varnished. Fibreglass serving (Class H, 180°C) is superior but requires fibreglass yarn, which NZ may be able to produce if glass fibre production is established (Doc #98).³³

NZ substitute wire insulation application — dependency chain: Applying shellac or oil-based insulation to copper wire at production scale requires: (1) a wire drawing setup producing bare copper wire to the correct gauge (see Doc #70 and Doc #105); (2) a continuous coating bath of dissolved shellac or polymerised oil; (3) a coating die or guide to apply a controlled coating thickness; (4) a drying/curing tunnel with controlled temperature (approximately 150–200°C for shellac, 180–220°C for linseed oil) long enough to cure the coating before the wire is wound onto a spool; (5) a winding mechanism with controlled tension; and (6) a source of heat (electric resistance, wood gas, or coal) sustained throughout the coating run. Cotton or fibreglass serving requires a wire serving machine — a rotating bobbin carrier that wraps thread around moving wire under controlled tension. Cotton thread is available from NZ textile stocks or potentially produced from NZ-grown flax (Linum usitatissimum); fibreglass yarn requires Doc #98 glass production capability (Phase 3+, [C]). None of these steps are trivial at production scale, though all are achievable with NZ workshop capability in Phase 2–3. [Feasibility: shellac/oil-coated wire Phase 2–3, [B]; cotton-served wire Phase 2, [B]; fibreglass-served wire Phase 3+, [C].]

Honest assessment: NZ-produced magnet wire insulation will be inferior to commercial enamel. Motors rewound with substitute insulation will need to be derated, will have shorter winding life, and will be physically larger (fewer turns fit per slot because the insulation is thicker) or will need to accept reduced performance. This is a real performance gap. A motor rewound with shellac-insulated cotton-served wire may deliver 60–80% of its original rating, depending on the insulation build-up thickness and the motor’s original thermal margin.³⁴ This is substantially better than a dead motor.

5.2 Copper supply

Copper for magnet wire can come from:

• Recycled motor windings: Every old motor that is rewound yields copper from the stripped winding. This copper can be remelted, drawn into wire, and insulated for the next rewind. The copper is not consumed — it is recycled through the system.
• Recycled electrical cable: Building demolition, infrastructure decommissioning, and cable replacement yield copper. NZ has significant copper in installed electrical cable — estimated at 50,000–150,000 tonnes in buildings, infrastructure, and equipment.³⁵
• Other recycled copper: Plumbing, heat exchangers, electronic waste.
• NZ copper mining: NZ has minor copper deposits. Historically, copper was mined at several locations (Kawau Island, Thames, Reefton). These deposits are small by global standards but potentially useful under isolation.³⁶
• Trade: Australian copper (from Mount Isa, Olympic Dam) is the likely long-term external source via sail trade (Doc #151, Doc #138).

The copper supply is unlikely to be the binding constraint for motor rewinding. The constraint is insulation — getting the copper wire properly insulated before it can be wound into a motor.

5.3 Slot insulation materials

Slot liners separate the copper winding from the grounded stator core and must withstand the motor’s operating temperature, the voltages present, and the mechanical forces during coil insertion and motor operation.

Commercial materials (imported, finite stock):

• Nomex (aramid paper) — Class H (180°C), excellent mechanical strength. The premium slot insulation.
• Mylar (polyester film) — Class B (130°C), good dielectric strength.
• DMD composite (Dacron-Mylar-Dacron) — Class F (155°C), combines mechanical strength with dielectric performance.

NZ-producible substitutes:

• Fish paper (vulcanised fibre): Made by treating rag paper or cotton linters with zinc chloride solution, which gelatinises the cellulose, then washing and drying. The result is a tough, flexible, electrically insulating sheet. Fish paper was the standard motor slot insulation before synthetic alternatives and remains adequate for Class A applications (105°C). NZ can produce this — dependency chain: (1) rag paper or cotton linter feedstock from NZ paper mills (Oji Fibre Solutions, Kinleith) or recovered cotton textiles; (2) zinc chloride solution (zinc metal dissolved in hydrochloric acid); zinc from existing commercial stocks or from smelting of galvanised steel, hydrochloric acid from salt + sulfuric acid (see Doc #116 for acid production); (3) tanks and processing vats for soaking treatment; (4) wash tanks and drying racks. The process does not require high temperatures or exotic chemistry, but does require controlled concentration of zinc chloride solution and thorough washing to remove zinc residues from the finished sheet. [Feasibility: Phase 2, [B].]³⁷
• Varnished rag paper or kraft paper: Paper impregnated with linseed oil varnish or shellac, then baked. Provides Class A insulation. The paper must be dense and free of pinholes. NZ paper mills (Oji Fibre Solutions at Kinleith) could potentially produce suitable paper with process development.
• Mica: NZ has mica deposits (though not commercially exploited at scale). Mica is an outstanding natural electrical insulator, rated to very high temperatures, and was historically used extensively in electrical equipment. If NZ mica deposits prove adequate, mica paper or mica flakes bonded with varnish would provide excellent slot insulation. This requires geological assessment.³⁸

5.4 Impregnation varnish

Varnish serves multiple functions: it fills air gaps in the winding (improving thermal conductivity and insulation), bonds turns together (improving mechanical strength), and provides moisture protection.

Commercial varnishes (imported, finite):

• Polyester or alkyd-based varnishes — Class F (155°C). The most common type in NZ rewind shops.
• Epoxy-based varnishes — Class H (180°C). Higher performance.
• All are solvent-based or water-based formulations using synthetic resins that NZ cannot produce.

NZ-producible substitutes:

• Shellac varnish: Shellac dissolved in methylated spirits (ethanol, NZ-producible from fermentation, Doc #163). Class A insulation. An excellent natural insulating varnish with a long history in electrical applications.
• Linseed oil varnish: Raw or boiled linseed oil, thinned with turpentine (from radiata pine resin distillation). Cures by oxidative polymerisation when baked. Provides reasonable moisture resistance and Class A insulation.
• Tung oil varnish: Superior moisture resistance to linseed. Thinned with turpentine.
• Rosin-based varnish: Rosin (pine resin, available from NZ radiata pine) dissolved in turpentine or alcohol. Provides brittle but reasonably insulating coating. Often combined with linseed oil to improve flexibility.
• Bitumen/asphalt-based compound: NZ has some natural bitumen deposits. Bitumen provides good moisture resistance but is limited to Class A temperatures and is not as mechanically tough as polyester varnish. It was used as a motor insulation compound in the early 20th century.³⁹
• Kauri gum varnish: NZ has significant kauri gum deposits (fossilised and semi-fossilised resin from Agathis australis), particularly in Northland. Kauri gum was historically a major varnish feedstock and has insulating properties that may be relevant to electrical applications, though this specific use has not been systematically tested.⁴⁰ Worth evaluating alongside shellac and oil-based options.

Honest assessment: NZ-produced varnishes are all Class A (105°C maximum), compared to commercial Class F (155°C) or Class H (180°C) products. This means rewound motors using NZ varnish run at lower permissible temperatures and must be derated. The performance gap is real but manageable for most applications — a derated motor still works, it is a motor running at reduced capacity rather than a motor that does not run at all. [Feasibility for NZ varnish production: Phase 2, [B] for shellac/linseed/tung oil varnishes given existing stocks and radiata pine turpentine; Phase 3, [B] for production at scale from domestically grown feedstocks.]

5.5 Bearings

Motor bearings are the most critical non-rewinding consumable. Deep groove ball bearings (6200 and 6300 series, with bore diameters from 10 mm to 100+ mm) are the most common type in electric motors.⁴¹ NZ does not manufacture ball bearings.

Existing NZ stock: Bearing distributors (CBC, Motion, NTN-SNR agents, SKF agents) and motor rewind shops hold stocks. NZ’s total bearing inventory is unknown but likely represents several years of normal replacement demand.

Depletion mitigation:

• Bearing recovery: Bearings from scrapped motors, vehicles, and other equipment can sometimes be reused if they are in acceptable condition. Proper cleaning, inspection (check for roughness, play, pitting), and relubrication can extend bearing life.
• Plain bearings (bronze bushes): For some applications where ball bearings are unavailable, bronze sleeve bearings can substitute. These can be cast (Doc #93) and machined (Doc #91) in NZ. [Feasibility: Phase 3, [B].] The substitution involves real performance penalties that must be understood: (a) friction losses are 2–5 times higher than ball bearings, increasing motor power consumption by 1–3% and requiring an oil lubrication system (ring oiler or wick oiler) with regular maintenance;⁴² (b) plain bearings have a maximum surface speed limit (the bearing’s pressure-velocity or PV limit, typically 1–3 m/s for bronze bushes running without forced lubrication) — most industrial induction motors run at 1,500 or 3,000 rpm, giving shaft surface speeds of 1–5 m/s at common shaft diameters; motors at the upper speed range may require forced-oil lubrication or babbitt (white metal) bearings rather than simple bronze bushes to remain within PV limits; (c) bronze bearings wear faster than ball bearings and must be periodically rebored and refitted. Despite these drawbacks, this was standard practice for electric motors before ball bearings became cheap and universal, and a motor on properly designed plain bearings runs — it is not a dead motor.⁴³
• Bearing maintenance: Regular relubrication (with tallow-based grease — Doc #34 — as petroleum grease stocks deplete), proper alignment, and vibration monitoring extend bearing life significantly. Many motor bearings fail prematurely due to over-lubrication, contamination, or misalignment — all preventable.
• Trade: Bearings are a high-value, low-volume import well suited to sail trade from Australia.

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6. WORKSHOP SETUP

6.1 Essential equipment for a motor rewind shop

A functional motor rewind workshop requires:

• Coil winding machine: A mandrel on a stand with a turns counter and hand crank or motor drive. Can be fabricated in a machine shop (Doc #91) — it is essentially a lathe adapted for winding wire onto a form.
• Burnout oven: A firebrick-lined oven with electric heating elements and a thermocouple for temperature monitoring. Size must accommodate the largest motors to be rewound. Can be constructed locally from refractory brick and heating elements salvaged from domestic ovens or purpose-wound resistance wire.
• Dip tank: A tank of sufficient size to immerse a stator in varnish, with a drain valve to recover varnish after each dip. Can be fabricated from mild steel plate by a welder — requires steel plate (1.5–3 mm), welding equipment, and a suitable drain fitting. Size is determined by the largest stator to be rewound; a tank 600 mm diameter × 600 mm deep handles most motors up to 75 kW frame size.
• Curing oven: For baking varnish after impregnation. Can be the same oven as the burnout oven (at lower temperature) or a separate unit. Temperature range: 130–180°C, with forced air circulation for even heating.
• Test equipment: Megger (insulation resistance tester), milliohmmeter or Wheatstone bridge (winding resistance), hi-pot test set (high-voltage insulation test), surge tester (turn-to-turn insulation test), ammeter, voltmeter. Of these, the megger is essential and non-negotiable. The surge tester and hi-pot set are highly desirable but rewinds were done without them for decades.
• Mechanical equipment: Bearing puller, press (arbor press or hydraulic press for bearing installation), crane or hoist (motors above approximately 30 kg are too heavy to handle manually), basic hand tools, wire strippers, soldering or brazing equipment.
• Storage: Dry, temperature-stable storage for magnet wire (moisture degrades enamel insulation), insulation materials, varnish, and bearings.

6.2 Minimum viable setup

A rewind shop can be established with remarkably little specialised equipment. The minimum viable setup:

• A work bench
• A coil winding form (can be improvised from wooden blocks)
• A megger
• A varnish dip tank (any suitable container)
• An oven (can be adapted from a domestic oven for small motors, or built from brick)
• Basic hand tools

This minimum setup can rewind small to medium motors (up to approximately 15 kW) at a rate of perhaps 2–5 motors per week. It will not produce the same quality as a well-equipped shop — the rewinds will be functional but with shorter expected life. For communities without access to a proper rewind shop, this minimum capability keeps critical motors running.

6.3 Geographic distribution

NZ’s motor rewind shops are concentrated in larger towns and cities. Rural communities — which depend heavily on motors for dairy, water pumping, and grain milling — may be hours from the nearest rewind capability.

Under recovery conditions, two strategies address this:

• Regional hubs: Establish well-equipped rewind shops in each region (one per former territorial authority or major town), capable of handling the full range of motor sizes.
• Mobile capability: Equip vehicles with portable rewinding equipment for field service to remote farms and communities. This was historically common in NZ — itinerant electricians and motor rewinders served rural areas from mobile workshops.

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7. TRAINING

7.1 Existing workforce

NZ’s motor rewinding workforce is small and aging. The motor rewinding trade has contracted as imported replacement motors became cheaper than rewinding for smaller units. Many experienced rewinders are in their 50s to 70s. The same knowledge-capture urgency described for aging specialists in Doc #160 (Heritage Skills Preservation) applies to motor rewinders — these individuals hold practical knowledge that is not written down and cannot be learned from a textbook.

7.2 Training pipeline

Motor rewinding builds on general electrician skills. The training path:

From qualified electrician to basic rewinder (3–6 months):

• Winding data recording and interpretation
• Stator stripping and core inspection
• Coil winding techniques (hand and machine)
• Coil insertion and connection
• Varnish impregnation
• Basic testing (megger, resistance, no-load run)
• Common motor types and their winding patterns

From basic to proficient rewinder (6–18 months additional):

• Non-standard winding configurations
• Larger motor rewinding (above 30 kW)
• Troubleshooting and diagnosis of complex faults
• Surge testing and interpretation
• Rotor assessment and repair
• Motor design fundamentals (sufficient to modify windings for different voltages or speeds)
• Training others

From proficient rewinder to motor design engineer (years of additional study):

• Motor electromagnetic design (flux density, slot geometry, winding factors)
• Thermal design (heat dissipation, temperature rise calculation)
• Mechanical design (bearing selection, vibration analysis)
• New motor design for NZ-specific applications

7.3 Training priority

The immediate priority is not training new rewinders from scratch — it is ensuring that existing rewinders’ knowledge is captured and that a cohort of electricians begins cross-training. The training model should be master-apprentice: each experienced rewinder takes 2–4 learners and trains them on actual rewinding jobs.

Te Pukenga polytechnics with electrical trade programs should add motor rewinding modules to their curricula, using existing rewind shop equipment at the polytechnics or through partnership with commercial rewind shops.

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8. PRIORITY MOTORS

When rewinding materials are scarce, not all motors can be repaired. The following prioritisation framework applies:

Tier 1 — Repair immediately (essential services)

• Town water supply pumps: Loss of a water supply pump means a town has no water. This is a public health emergency.
• Hospital essential services motors: Ventilation, water, medical equipment drives.
• Dairy shed vacuum pump and milk pump motors: Dairy herds must be milked at least daily. A failed milking system motor means the herd cannot be milked — leading to animal welfare crisis and loss of milk production.
• Grain milling motors: Grain must be milled for human consumption. A failed mill motor halts flour production for the community it serves.

Tier 2 — Repair promptly (economic productivity)

• Irrigation pump motors: Especially during drought years, which remain a recurring feature of NZ’s eastern regions regardless of post-event conditions. Nuclear winter effects on NZ precipitation are uncertain — temperature reductions may reduce evapotranspiration demand while changing storm patterns in ways that are not reliably predictable from existing models.⁴⁴
• Machine tool motors (Doc #91): A machine shop without power is a dead shop.
• Sawmill motors: Timber production for construction and trade.
• Cool store and freezer motors: Food preservation and storage.
• Sewage pump motors: Public health infrastructure.

Tier 3 — Repair when capacity allows

• General industrial motors: Processing, manufacturing, commercial operations.
• Farm equipment motors: Non-critical agricultural applications.
• Domestic motors: Household appliances. These are individually low-priority but collectively important for quality of life and household food preservation (refrigerators, freezers).

8.1 Triage criteria

When two motors compete for the same scarce magnet wire, the decision should consider:

• Number of people affected: A town water pump serves thousands; a farm workshop motor serves one family.
• Availability of alternatives: Can the function be performed manually? Milking by hand is possible for small herds but not for large dairy operations.
• Motor size: A small motor uses less wire than a large one. Two small motors rewound for the wire cost of one large motor may serve more people.
• Condition of motor frame and core: A motor with a damaged core is a poor investment of scarce wire — it will have high losses and short winding life. A motor with a clean core is a better candidate.

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CRITICAL UNCERTAINTIES

Uncertainty	Impact	Mitigation
NZ motor rewind shop count and distribution	Cannot plan coverage if unknown	Census (Doc #8) — motor rewind shops as specific category
National magnet wire stock	Determines depletion timeline — could be 4 years or 20	National inventory — highest priority
NZ enamel substitute performance	Determines whether NZ-wound wire is practical	R&D program — testing shellac, linseed, tung oil, cotton serving
Motor fleet annual failure rate under post-event conditions	Determines rewinding demand	Monitor and record failure rates from Year 1
Bearing stock nationally	Determines when bearing alternatives must be deployed	Bearing distributor inventory — Phase 1
NZ mica deposit suitability	Could provide high-performance insulation from local materials	Geological assessment — Phase 2
Stator core damage during burnout	Determines what fraction of rewound motors perform well	Strict burnout temperature control; core loss testing
Copper wire drawability to magnet wire gauges	Determines whether NZ bare wire can substitute for imported	Drawing trials — Phase 2
Rewinder workforce age profile	Determines knowledge capture urgency	Skills census (Doc #8)

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CROSS-REFERENCES

• Doc #1 — National Emergency Stockpile Strategy (magnet wire, bearings, and insulation materials as strategic stocks)
• Doc #8 — National Skills and Asset Census (rewind shops, rewinder skills, motor populations at critical facilities)
• Doc #34 — Lubricant Production (tallow-based bearing grease as petroleum grease substitute)
• Doc #65 — Alcohol Production (ethanol as shellac solvent and general industrial solvent)
• Doc #65 — Hydroelectric Station Maintenance (generator rewinding shares skills with motor rewinding)
• Doc #67 — Transpower Grid Operations (reliable grid supply is prerequisite for motor-driven economy)
• Doc #70 — Transformer Rewinding (shared skills, shared copper wire supply, cross-training workforce)
• Doc #74 — Pastoral Farming (dairy shed motors as critical agricultural infrastructure)
• Doc #91 — NZ Steel (potential source of electrical steel laminations; steel for motor frames)
• Doc #91 — Machine Shop Operations (fabrication of winding machines, forms, and test equipment; machining of motor shafts and housings)
• Doc #93 — Foundry and Casting (rotor casting in aluminium; bronze bearing casting)
• Doc #98 — Glass Production (potential source of glass fibre for insulation)
• Doc #105 — Fencing Wire and Wire Drawing (copper wire drawing capability development)
• Doc #138 — Sailing Vessel Design (trade route for copper, bearings, and magnet wire from Australia)
• Doc #157 — Trade Training Priorities (motor rewinding as critical trade skill)
• Doc #160 — Heritage Skills Preservation (rewinding knowledge from aging workforce)

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1. NZ electric motor population estimate is inferred from the number of industrial, agricultural, and commercial premises, typical motor counts per facility, and household appliance data. Stats NZ business demography data indicates approximately 560,000 business enterprises in NZ; a significant fraction of these use electric motors. EECA (Energy Efficiency and Conservation Authority) data indicates electric motors account for approximately 30% of NZ’s total electricity consumption, concentrated in the industrial and commercial sectors. https://www.eeca.govt.nz/ The 3–6 million figure includes household appliance motors (each household typically contains 5–15+ motors across refrigerators, washing machines, fans, power tools, etc.) and is a rough estimate — no comprehensive NZ motor census has been conducted.↩︎

2. Induction motor principles and construction are standard electrical engineering. See: Fitzgerald, A.E. et al., “Electric Machinery,” McGraw-Hill, various editions; Hughes, A. and Drury, B., “Electric Motors and Drives,” Elsevier, 5th edition. Three-phase squirrel-cage induction motors dominate industrial applications because of their simplicity, robustness, and lack of commutator or brushes. Service life depends on insulation class, operating temperature, and bearing maintenance.↩︎

3. NZ motor imports: Stats NZ Infoshare, Harmonised System codes 8501 (electric motors and generators). NZ’s motor imports include units from WEG (Brazil), Siemens (Germany), ABB (Switzerland/global), Teco (Taiwan), and numerous Chinese manufacturers. NZ has no electric motor manufacturing capability.↩︎

4. NZ motor rewind industry estimate: There is no published directory of NZ motor rewind shops. The estimate of 30–80 shops is based on Yellow Pages listings, industry contacts, and the number of NZ towns large enough to support a rewind operation. The New Zealand Electrical Contractors Association (NZECA) and Master Electricians may have more complete data. The workforce estimate of 100–300 rewinders follows from the shop count (typically 2–5 rewinders per shop).↩︎

5. National magnet wire stock estimate: Highly uncertain. Based on typical rewind shop inventories (a medium shop might hold 0.5–3 tonnes across all wire gauges) multiplied by shop count, plus distributor holdings. This figure requires verification through the national inventory. Major magnet wire distributors in NZ include Rexel (formerly PDL Electric), Edisons, and specialist electrical suppliers.↩︎

6. Motor failure mode distribution: IEEE Standard 493 (Recommended Practice for the Design of Reliable Industrial and Commercial Power Systems, “Gold Book”) provides motor failure mode statistics based on large-scale industry surveys. Bearing failure consistently accounts for the largest share. Also: EASA (Electrical Apparatus Service Association), “Effect of Repair/Rewinding on Motor Efficiency,” 2003 — a major industry study on motor reliability and repair.↩︎

7. Motor rewinding labour hours: Based on industry practice and EASA technical publications. Actual times vary widely with motor size, type, winding complexity, and shop equipment. The figures given are for a competent rewinder with standard shop equipment.↩︎

8. Economic case for motor rewinding: A complete cost-benefit analysis would require data on: actual motor failure rates under post-event conditions (likely higher than IEEE 493 peacetime figures due to deferred maintenance and harsher operating conditions); rewinding throughput achieved in practice; and the productive value of the operations each motor supports. The qualitative case is strong, but a formal analysis should be developed from Year 1 operational data.↩︎

9. Induction motor principles and construction are standard electrical engineering. See: Fitzgerald, A.E. et al., “Electric Machinery,” McGraw-Hill, various editions; Hughes, A. and Drury, B., “Electric Motors and Drives,” Elsevier, 5th edition. Three-phase squirrel-cage induction motors dominate industrial applications because of their simplicity, robustness, and lack of commutator or brushes. Service life depends on insulation class, operating temperature, and bearing maintenance.↩︎

10. NZ dairy herd count: DairyNZ statistics. As of 2023, NZ had approximately 10,800 dairy herds with approximately 4.7 million dairy cows. https://www.dairynz.co.nz/about-us/about-the-industry/ Under nuclear winter conditions, herd numbers would decrease (Doc #74, Doc #75) but the remaining herds would still need functioning milking equipment.↩︎

11. NZ dairy sector economic significance: DairyNZ and Stats NZ agriculture statistics. Dairy exports consistently account for approximately 25–30% of NZ’s total merchandise exports by value — the largest single agricultural export category. See DairyNZ Economic Survey, annual. https://www.dairynz.co.nz/ For nutritional protein contribution, note that beef, lamb, and seafood are also major protein sources for NZ households; dairy contributes primarily fat, calcium, and protein but is not the sole or dominant protein source for the population.↩︎

12. NZ territorial authorities and water supply: Department of Internal Affairs data on local government. NZ has 67 territorial authorities (district and city councils), each responsible for water supply. Water Infrastructure Commission of NZ (later Three Waters Reform) documented the state of NZ’s water infrastructure. https://www.dia.govt.nz/↩︎

13. IEC motor frame sizes: IEC 60034-1 (Rotating electrical machines — Rating and performance) and IEC 60072 (Dimensions and output series for rotating electrical machines) define the standard frame sizes used in NZ and most of the world outside North America. NZ uses IEC/metric frames (as does Australia, the UK, and continental Europe).↩︎

14. Motor annual failure rates: IEEE Standard 493 reports motor failure rates of 0.0132–0.0613 failures per unit per year for different motor types and applications (roughly 1–6% per year). The higher rates apply to motors in harsh environments (chemical, mining, outdoor). IEEE Power and Energy Society, “IEEE Recommended Practice for the Design of Reliable Industrial and Commercial Power Systems,” IEEE Std 493-2007.↩︎

15. Motor failure mode distribution: IEEE Standard 493 (Recommended Practice for the Design of Reliable Industrial and Commercial Power Systems, “Gold Book”) provides motor failure mode statistics based on large-scale industry surveys. Bearing failure consistently accounts for the largest share. Also: EASA (Electrical Apparatus Service Association), “Effect of Repair/Rewinding on Motor Efficiency,” 2003 — a major industry study on motor reliability and repair.↩︎

16. Insulation thermal aging: The Arrhenius relationship as applied to motor insulation life is documented in IEEE Standard 117 (Standard Test Procedure for Evaluation of Systems of Insulating Materials for Random-Wound AC Electric Machinery) and IEC 60034-1. The “10°C rule” (halving of insulation life per 10°C temperature increase) is a well-established approximation, though the actual relationship varies with insulation chemistry.↩︎

17. Insulation resistance testing: IEEE Standard 43 (Recommended Practice for Testing Insulation Resistance of Electric Machinery) provides comprehensive guidance. The “1 megohm per kV + 1” rule is a commonly used minimum acceptable value. Higher values are expected for new or rewound windings.↩︎

18. Surge comparison testing: EASA Technical Manual, Section on “Surge Testing.” A surge tester applies a high-voltage impulse (typically 1,000–5,000V, depending on motor rating) to each phase winding and displays the resulting damped oscillation on an oscilloscope or digital display. Identical waveforms between phases indicate a healthy winding. Differences indicate turn-to-turn shorts or insulation weakness.↩︎

19. Growler test: A traditional test described in motor repair texts such as Rosenberg, R., “Electric Motor Repair,” Holt, Rinehart and Winston, various editions. The growler is an electromagnet that magnetises the rotor; a thin metal strip held against the rotor surface vibrates over broken bars due to the discontinuity in the magnetic circuit.↩︎

20. Motor rewinding procedures: EASA Standard AR100, “Recommended Practice for the Repair of Rotating Electrical Apparatus.” Also: Rosenberg, R., “Electric Motor Repair,” and Nailen, R.L., “Managing Motors,” — both standard industry references. EASA (Electrical Apparatus Service Association) is the primary international industry body for motor repair and rewind shops.↩︎

21. Burnout temperature limits: EASA Standard AR100 specifies maximum burnout temperature of 343°C (650°F) for oven temperature, measured at the core. Temperatures above this risk damaging the interlaminar insulation of the stator core, which increases core losses. EASA, “Effect of Repair/Rewinding on Motor Efficiency,” 2003 — a comprehensive study that documented the relationship between burnout temperature and core loss increase.↩︎

22. Core loss testing: EASA Standard AR100 recommends core loss testing after burnout and before rewinding. The test involves temporarily winding an excitation coil around the core, energising it at rated flux density (typically 1.0–1.5 T), and measuring the power drawn. Results are compared to expected values from core loss tables or to the pre-burnout measurement (if available).↩︎

23. Insulation class derating: IEC 60034-1 defines insulation classes and their associated temperature limits. Class A (105°C maximum hot spot) limits the temperature rise to approximately 60°C above ambient. Modern motors are typically Class F (155°C) or Class H (180°C). Downgrading from Class F to Class A insulation means the motor’s permissible temperature rise drops from approximately 105°C to 60°C — effectively requiring it to run at 60–75% of its rated power to stay within thermal limits.↩︎

24. Varnish impregnation process: EASA Standard AR100 describes dip and bake, flood, trickle, and VPI (vacuum pressure impregnation) methods. Dip and bake is the most common method in small to medium rewind shops. Curing temperatures and times depend on the varnish type — polyester varnishes typically cure at 150–180°C for 4–8 hours.↩︎

25. Motor rewinding labour hours: Based on industry practice and EASA technical publications. Actual times vary widely with motor size, type, winding complexity, and shop equipment. The figures given are for a competent rewinder with standard shop equipment.↩︎

26. Insulation resistance testing: IEEE Standard 43 (Recommended Practice for Testing Insulation Resistance of Electric Machinery) provides comprehensive guidance. The “1 megohm per kV + 1” rule is a commonly used minimum acceptable value. Higher values are expected for new or rewound windings.↩︎

27. Magnet wire specifications: IEC 60317 series (Specifications for particular types of winding wires). Enamel thickness (build) is specified by grade — Grade 1 (minimum build) to Grade 3 (heavy build). Typical enamel thickness for a 1.0 mm diameter wire is approximately 0.03–0.08 mm per side, depending on grade.↩︎

28. National magnet wire stock estimate: Highly uncertain. Based on typical rewind shop inventories (a medium shop might hold 0.5–3 tonnes across all wire gauges) multiplied by shop count, plus distributor holdings. This figure requires verification through the national inventory. Major magnet wire distributors in NZ include Rexel (formerly PDL Electric), Edisons, and specialist electrical suppliers.↩︎

29. Magnet wire manufacturing process: Described in industry references. The enamel coating tower is a vertical oven through which the wire passes multiple times, receiving a thin coat of liquid enamel at the bottom and curing it during the upward pass through the heated section. A typical tower is 10–30 m tall and operates at 400–600°C. The wire may make 6–20 passes to build up the required insulation thickness.↩︎

30. Shellac as electrical insulation: Shellac was the standard electrical insulating varnish from the 1870s through the 1940s, before synthetic polymers replaced it. It is dissolved in methylated spirits (ethanol) to form a varnish that can be applied by dipping or brushing. Its temperature rating is approximately 90–105°C (Class A). Shellac is produced from lac, a resin secreted by the lac insect (Kerria lacca), primarily in India and Thailand. NZ has no natural source. See: Von Fischer, W. and Bobalek, E.G., “Organic Protective Coatings,” Reinhold, 1953.↩︎

31. Linseed oil as insulation: Linseed oil (from Linum usitatissimum, common flax — not harakeke/NZ flax) polymerises by oxidation to form a tough, insulating film. It was used as a wire insulation and varnish component before synthetic alternatives. NZ grows linseed in Canterbury and other regions. See: Lambourne, R. and Strivens, T.A., “Paint and Surface Coatings,” Woodhead Publishing, 1999.↩︎

32. Tung oil: Derived from the seeds of the tung tree (Vernicia fordii). Tung trees were planted in NZ, particularly in Northland, for oil production in the early-mid 20th century. Some plantings remain. Tung oil is a superior drying oil with excellent water resistance. See: Soucek, M.D. et al., “Drying oils,” in Kirk-Othmer Encyclopedia of Chemical Technology.↩︎

33. Cotton-served and fibreglass-served magnet wire: Pre-enamel magnet wire was insulated by wrapping with cotton thread, then varnishing. This was standard practice through the early 20th century and remains a viable method. Cotton-served wire is thicker than enamel-insulated wire of the same conductor diameter, reducing the number of turns that fit in a slot. Fibreglass serving provides higher temperature ratings (Class H, 180°C). See: IEC 60317 series; also historical motor repair texts from the pre-enamel era.↩︎

34. Derating estimate for substitute wire insulation: The 60–80% of original rating figure is a working estimate based on the thermal derating required when downgrading from Class F insulation (155°C maximum hot spot, 105°C temperature rise above 50°C ambient) to Class A (105°C maximum hot spot, approximately 60°C temperature rise). Under IEC 60034-1, temperature rise ratings scale approximately linearly with insulation class limits above ambient. The additional derating for thicker insulation (fewer turns per slot, requiring fewer turns or smaller wire gauge, both of which reduce the motor’s magnetic flux and therefore its torque capability) adds a further variable. The range reflects these combined uncertainties. Practical derating values should be established through testing of rewound motors — this figure requires verification from rewinding trials. See: IEC 60034-1:2022, Table 3 (temperature limits for insulation classes).↩︎

35. NZ installed copper estimate: Based on per-capita copper use data and NZ’s building stock. The International Copper Study Group estimates global in-use copper stock at approximately 35–55 kg per capita in developed countries. For NZ’s population of approximately 5 million, this suggests 175,000–275,000 tonnes total, of which a significant fraction is in electrical wiring. The 50,000–150,000 tonne estimate for wire and cable is a rough subset of this total.↩︎

36. NZ copper mining history: Copper was mined at several NZ locations, including Kawau Island (1840s–1860s), Thames (1870s–1880s), and minor occurrences in Nelson and Otago. None of these deposits were large by global standards. GNS Science holds geological survey data on NZ mineral deposits. https://www.gns.cri.nz/ Whether any NZ copper deposits could be economically reworked under isolation conditions requires geological and economic assessment.↩︎

37. Fish paper (vulcanised fibre): Made by treating cellulose (cotton linters or rag paper) with zinc chloride solution, which swells and partially dissolves the cellulose, forming a tough, dense material after washing and drying. Vulcanised fibre was the standard motor slot insulation material in the early 20th century and is still used in some applications. It is rated Class A (105°C). The manufacturing process is documented in: Satas, D., “Handbook of Pressure Sensitive Adhesive Technology,” and historical electrical insulation references.↩︎

38. NZ mica deposits: Mica (muscovite and biotite) occurs in NZ, particularly in schist formations in Otago and metamorphic rocks in other regions. NZ mica has not been commercially exploited for electrical insulation purposes. The quality and quantity of NZ mica deposits for electrical applications requires geological assessment. See: GNS Science mineral resources database.↩︎

39. Bitumen/asphalt insulation compounds: Bitumen-based compounds were used as motor insulation and cable jointing materials in the early electrical industry. NZ has some natural bitumen occurrences and can also produce bitumen from coal tar (a byproduct of coal gasification or coking). Temperature rating is limited (Class A or below) and mechanical properties are inferior to modern varnishes.↩︎

40. Kauri gum: Fossilised and semi-fossilised resin from kauri trees (Agathis australis), historically a major NZ export used in varnish and linoleum manufacture. NZ has significant kauri gum deposits, particularly in Northland. Kauri gum varnish has insulating properties that may be relevant to electrical applications, though this specific use has not been systematically tested. See: Reed, A.H., “The Story of Kauri Gum,” A.H. & A.W. Reed, various editions.↩︎

41. Motor failure mode distribution: IEEE Standard 493 (Recommended Practice for the Design of Reliable Industrial and Commercial Power Systems, “Gold Book”) provides motor failure mode statistics based on large-scale industry surveys. Bearing failure consistently accounts for the largest share. Also: EASA (Electrical Apparatus Service Association), “Effect of Repair/Rewinding on Motor Efficiency,” 2003 — a major industry study on motor reliability and repair.↩︎

42. Plain bearings in electric motors: Before the widespread adoption of ball bearings (from approximately 1920 onward), electric motors used plain bronze or babbitt bearings. These require regular oiling (typically through ring oilers or wick oilers), produce more friction losses, and need periodic reboring and refitting as they wear. But they function and can be manufactured in NZ. See: Wilcock, D.F. and Booser, E.R., “Bearing Design and Application,” McGraw-Hill; also historical motor design references from the pre-ball-bearing era.↩︎

43. PV limits for plain bearings in electric motors: The bearing PV (pressure × velocity) limit characterises the maximum combination of bearing load and shaft surface speed a plain bearing can sustain without excessive heat generation. For bronze bushes (cast tin-bronze, SAE 660 equivalent), the continuous PV limit is typically 1.75–3.5 MPa·m/s under oil lubrication, lower under grease or wick oiling. For a 4-pole 1,500 rpm motor with a 32 mm shaft diameter (common for 5.5–11 kW frame 132 motors), the shaft surface speed is approximately 2.5 m/s — within the PV limit at light loads but potentially marginal at full load. For 2-pole 3,000 rpm motors (shaft surface speed approximately 5 m/s on the same shaft), PV limits may be exceeded under full load and forced oil lubrication or babbitt bearings may be required. Each motor requiring plain bearing substitution should be evaluated individually. See: Shigley, J.E. and Mischke, C.R., “Mechanical Engineering Design,” McGraw-Hill; also SAE J459 (Bearing and Bushing Alloys).↩︎

44. Nuclear winter effects on NZ precipitation: The climate modelling literature on nuclear winter primarily addresses temperature and light reduction; precipitation effects are complex and region-dependent. For NZ specifically, large-scale circulation changes under nuclear winter cooling could alter the pattern of westerly weather systems and block high pressure events that drive eastern NZ drought, but could also reduce convective precipitation. There is insufficient published modelling of NZ regional precipitation response under nuclear winter to make confident directional claims. See general nuclear winter climate literature: Robock, A. et al., “Nuclear winter revisited with a modern climate model and current nuclear arsenals,” Journal of Geophysical Research, 2007; Coupe, J. et al., “Nuclear Niño response observed in simulations of nuclear war scenarios,” Communications Earth & Environment, 2019.↩︎