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I was under the impression that 2 pole circuits that feed 240 volts are always wired with 12/3 wire (2 hots, one neutral and one ground). With this wire, the two hots attach to the two lugs on the dual pole breaker and the neutral and ground go to their respective buses.

However, I am finding instances where a circuit is 240V but driven using 12/2 Romex, with the black and white wire attached to the two lugs. My reading suggests that this is code compliant.

But I am confused as to how the current is returning to the neutral bus? If a neutral is not required, why would anyone ever use a */3 wire? ..

Ed Beal
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cryptic0
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  • It does, thank you. The answers below provides better context using examples, so may be let's keep the question? – cryptic0 Jun 02 '22 at 16:59
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    I can't delete this even if I wanted to. Duplicate closure simply acknowledges there are more (usually better) answers already given – Machavity Jun 02 '22 at 17:06
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    This question also asks or references size that the tester answer doesn’t as it was not in that question. – Ed Beal Jun 02 '22 at 17:31

3 Answers3

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2 pole 240v circuits are only required to be 12 awg if a 20 amp breaker. In 240 only the white should be re identified but going directly to a breaker it is usually not or called out by inspectors but the load side is.

A 15 amp double pole or 240v circuit can be run with 14awg wire.

You would be required to run X3 with ground so 4 wires if installing a sub panel or a device like a dryer that requires 240 for the heating element and 120 for the motor (just one of hundreds of possible needs for X3 wire)

Ed Beal
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Only 240 volts devices needing the neutral wire require 12/3 or larger.

Quite a few devices to not need the neutral wire and are quite happy with just two hots and a ground. Devices like hot water tanks, welders, some heaters.

Neutral is usually required when something attached to the device requires 120 volts only, stoves with lights/clocks.

With 240/two hots, each hot works opposite to the other hot at 60 times a second, 60hz.

crip659
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Because you don't need neutral for a 240V only circuit. So you don't need 3 wires + ground, and cable (here) comes black, white, ground when you only have 2 wires + ground.

You should (and people, even Licensed electricians, often don't) remark the white wire with a hot color (I prefer red, it's more obviously not a random bit of electrical tape, but black is acceptable, as are blue, pink, purple, brown, yellow, orange...)

The current in a (USA/Canada) 240V circuit does not flow in the neutral at all. It goes from Hot to the other Hot. The grounded neutral is a center tap on the 240V secondary of the supply transformer, which is why each hot is 120V to ground, but there's 240V from hot to hot.

You only need a neutral wire in the case that there is a need for 120V on the circuit - which is then not a 240V-only circuit.

Ecnerwal
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    Yes, the white wire in my panel was not marked with a red by the electrician. Hence my confusion. The circuit is feeding fan heaters. – cryptic0 Jun 02 '22 at 17:00
  • @cryptic0 I think I see your confusion. On some 240 volt circuits that do not need a neutral(usually white) wire, the second insulated wire in the cable can be used as a hot wire. If it is a white wire it should(but half the time is not) be marked with a hot colour at both ends. – crip659 Jun 02 '22 at 18:42
  • @cryptic0 Yes, the Code requirement for "marking always" came in, in the last 10-15 years. Before that, marking could be skipped "if the usage was obvious". Many (most?) electricians refuse to follow the new "always" rule, and many inspectors let them get away with it. Generally an inspector has bigger fish to fry. – Harper - Reinstate Monica Jun 02 '22 at 18:57
  • Fan heaters, eh? If you can come up with some money (once) for an upgrade to cold-climate mini-split heat pump, you can save a lot of money (over time) on running cost .vs. resistance heaters... – Ecnerwal Jun 02 '22 at 18:59
  • White can be marked as a hot wire, you cannot mark or use other colours than white(or grey) to use as neutral, except for large gauge(like the feeder wires from the pole). – crip659 Jun 02 '22 at 19:50