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I have an unused 3 wire 220V 55 amp circuit from the meter from my old A/C unit running right where I need a 20 amp 3 wire 220v, is there a way to reduce the circuit, put in a remote 20 amp breaker safely without changing the main breaker?

  • Is there a breaker at the AC unit, or only at the service panel? – Harper Jun 18 at 18:59
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    When you say "3 wire 220V" do you mean 2 hots and neutral (like an obsolete dryer or range connection) or 2 hots and ground (like a compressor welder tanning bed table saw etc.)? – Harper Jun 18 at 19:01
  • Is the disconnect for the A/C a fusible or a non-fusible type, and do you need neutral or not? Also, what wiring method was used for the existing circuit? – ThreePhaseEel Jun 18 at 22:50
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Your current circuit, going to a large air conditioning unit, is almost assuredly 2-wire hot-hot + ground.

The important part here is that you will not be able to power a load that requires hot-hot-neutral (and often ground). This is very important. You cannot re-task the current ground wire to be a neutral.

However, most of the 20A 240V loads I can think of do not require a neutral. If they plug into a NEMA 6 type receptacle, you are all set.

Change the breaker —— The best way to do this is change the circuit breaker in the main panel which feeds this circuit. If there is still a shutoff switch, fuse or second breaker that is 50A, that does not matter. The breaker in the main panel will sufficiently protect the circuit.

You can then attach it to a NEMA 6-20 receptacle. These come in both single or doubles. Read the documentation with your 240V device; if it requires a dedicated circuit use a single receptacle, otherwise feel free to use a double.

You may have trouble attaching the heavy 6 AWG wire to a 20A breaker or receptacle. If so, use a 12 AWG pigtail. You can attach the two wires with a large (red or tan) wire nut.

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You could certainly add a 20A breaker in a box somewhere down the line, but if you don't use the line at all at present, why not just swap the breaker from 55A to 20A for the time being? Depending on the terminals you might need to have a pigtail to fit the 20A breaker and join to the current wire, but that's not a big deal. If you later develop some additional use, you can address wiring for that, at that point.

  • What are you calling a three wire ? Two hots and a ground or neutral.Or four wires ,two hot ,one ground one neutral.It is going to matter. Are wires run in metal conduit or cable? – user101687 Jun 18 at 18:44
  • Going to have to make one wire the hot to breaker and add pigtail to fit breaker. Add white tape on both ends of wire to re,id neutral and put on neutral bar if sub-panel.Then bare ground to ground bar. If it is main panel both go on the same bar as rest of panel.. Can you send pic of ac disconnect may even be able to make out door panel if room. add pigtails to fit on to Gfci outlet and add in use cover for code. – user101687 Jun 18 at 18:57
  • What type of set up is out doors a circuit breaker or a pull out disconnect ? – user101687 Jun 18 at 19:05
  • 2 hots and one neutral, no [bare wire] ground – Dan H Jun 19 at 19:23
  • In that case you are either going to need to add a ground wire (unless it runs in metallic conduit) or otherwise re-think this. – Ecnerwal Jun 19 at 22:04

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