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Garage has 100A service sub-panel from main home. The panel contains a 40A 240V breaker. This connects through a heavy-gauge wire (looks to be same wire as feeding the 100A panel itself) to what I think is only a 15A outlet. That is, based on the physical dimensions and prong arrangement compared to info I found online, I believe this is a NEMA #6-15R receptacle. Am I right?

If the rest of the circuit is 40A but the outlet 15A, then I think this would be undersized and dangerous? Would it be appropriate to replace this #6-15R with a #6-30R? Do I also need to put in a 30A breaker?

The reason this came up is that I would like to use a 20A 240V heater in the garage. The heater uses a #6-30P plug, which can be seen dangling in one of the photos below. Basically, I am looking for a safe way to clean up the electricals, in a way that will make the end result compatible with this NEMA #6-30P heater.

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    Can you post better photos of both the receptacle and the breaker box please? – ThreePhaseEel Jan 3 at 2:44
  • @jsotola - sorry! No, you cannot plug a regular 120V cable into that receptacle. Hopefully the new photo shows this better. – Roberto Jan 3 at 4:12
  • @ThreePhaseEel - sorry for the poor photos. I tried again with a tripod and added some (hopefully) clearer photos of what I think you had requested. Please let me know if not. – Roberto Jan 3 at 4:13
  • @jsotola that was a trick of the light. The new photos show plain. It's a 6-15. – Harper Jan 3 at 4:21
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Change the 2-pole breaker to a Square D Homeline 30A breaker ($9). Make sure that cable is at least 10 AWG (8 or 6 will do).

Then fit a NEMA 6-30 as you intend.

Then replace those two 15A 1-pole breakers with Square D Homeline 15A breakers. If they power one cable with a shared neutral, use a 2-pole breaker.

Those Siemens QP breakers have no business in your panel. Donate those to someone with a Siemens/Murray panel. This isn't brand loyalty, the breakers do not fit properly and will arc.

  • this is great info, thank you! I will have to read up on identifying shared neutrals, but that would be another question if needed. – Roberto Jan 3 at 10:29

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