Electrical – 240v 4wire power supply 30 amp breaker,240v 3wire air compressor switch

electrical

240v power supply has 4 wires red black white ground. my 240v air compressor only has 3 wires white, black,and ground. how do I connect it?

Best Answer

EDIT: I am assuming this question is saying the compressor has white, black, and green leads in the peckerhead.

In the US, the four wire supply should be

  • Black - L1 (maybe L2 - doesn't matter)
  • Red - L2 (maybe L1 - doesn't matter)
  • White - Neutral
  • Green - Ground

To test, you should see the following voltages:

  • Black to Red = 240V
  • Black to White = Red to White = Black to Green = Red to Green = 120V
  • and you should read continuity between White and Green.

If the compressor is 240V, it doesn't follow the typical color coding; the white wire is ungrounded. The Green on the compressor should be ground, to test you should see continuity between the Green wire and the metal frame of the compressor. That leaves the black and white on the compressor for the 240V power. The white on the compressor should NOT show continuity to the Green wire or the metal frame. (Neither should the black wire on the compressor, for that matter, but it's the white that's off color code and I'd want to carefully verify is power.)

So after all that testing, it's simply

  • Supply Black to Compressor Black
  • Supply Red to Compressor White
  • Supply Green to Compressor Green
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