How Much Copper Is in a Motor or Transformer
Yields per tonne of whole units, by size and construction. The number most people want is a single percentage; the useful answer is that it moves with size in a direction that surprises them — copper share rises from small to medium and then falls again, because iron piles up faster than winding does.
Motors — yield per tonne
Share of gross weight as received, and the same figure as kg recovered from one tonne.
| Type | Cu | Si-steel | Al | Cu kg/t |
|---|---|---|---|---|
Small Motor (<5kW) Small wound motor, Cu winding ~12–22%, Al die-cast rotor | 16% | 58% | 8% | 160 |
Medium Motor (5–37kW) General industrial motor, Cu stator coil, Si-steel rotor | 18% | 57% | 5% | 180 |
Large Motor (>37kW) Large industrial motor, higher Fe% as size increases | 15% | 62% | 3% | 150 |
VFD/Servo Motor PM servo or VFD motor; rare earth magnets calculated separately | 20% | 55% | 7% | 200 |
Transformers — yield per tonne
Share of gross weight as received, and the same figure as kg recovered from one tonne.
| Type | Cu | Si-steel | Al | Cu kg/t |
|---|---|---|---|---|
Distribution TX (Oil) Oil-filled; ~15-20% insulating oil not in metal calc | 20% | 55% | 0% | 200 |
Dry-Type TX (Epoxy) Epoxy cast, no oil, relatively higher Cu% | 25% | 55% | 0% | 250 |
Al-Winding Distribution TX Aluminum winding, common in LV distribution | 0% | 55% | 20% | 0 |
Power TX (>1MVA) Large power TX; higher Fe%, lower Cu% relatively | 12% | 65% | 0% | 120 |
Bigger is not richer
Read the copper column down the motor table: 16% for small units, 18% for mid-range, then back down to 15% above 37 kW. A tonne of large industrial motors yields roughly 30 kg less copper than a tonne of mid-range ones.
The reason is structural. Winding cross-section scales with current; the stator and rotor iron scales with the torque the frame has to carry. Past a certain size the iron wins, and the casing gets heavier too. Buying whole motors by gross weight at one flat price therefore overpays for the large ones and underpays for the mid-range — which is exactly the mix a seller will send if the price is flat.
Servo and VFD motors go the other way (20%), and often carry rare-earth magnets that are not in any of these percentages. Sort those out before quoting, not after.
Transformers: three things that are not metal
Oil. An oil-filled distribution transformer carries roughly 15–20% of its shipped weight as insulating oil. That weight is in the gross you pay for and produces no metal. Older units may contain PCBs, which turns disposal from a cost line into a compliance problem — establish the year of manufacture before it arrives at your yard, not after.
The winding might be aluminium. Low-voltage distribution units are frequently wound in aluminium, and the outside of the unit looks identical. That single fact moves the metal value by more than any negotiation over percentages will.
Silicon steel is not ordinary scrap steel. Grain-oriented core laminations sell above common steel scrap when they come out clean and unsheared. Shredding a core destroys that premium.
Using these numbers to quote
Labour is the term people leave out, and on small motors it is decisive: the copper in a 5 kW motor is worth little enough that stripping it by hand can cost more than the metal. Batch size, not the percentage table, decides whether small units are worth taking at all.
All percentages are empirical midpoints for whole units as received, not standard values. A copper-rotor motor and an aluminium die-cast rotor of the same rating can differ by ten points. Sample and weigh before committing on a large lot.