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I’ve got a 30 amp breaker currently connected to my outside A/C condenser and I’m planning on adding a steam shower to the basement bathroom that requires a 20amp gfci breaker. There is a conjunction box mounted underneath my floor joists where a 220v circuit (from breaker) has a splice between the 10 gauge wire that joins another length of 10 gauge the remaining length outside to the condenser. What I wanted to do was connect another 220 V circuit in that box and run it over to the bath and upgrade to a gfci breaker using 10 gauge as well (steam shower requires 12).

Is this an okay solution? I would basically have A/C and steam shower running off one GFCI breaker, which I plan to upgrade to 50amp.

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  • Running a 30 and 20 amp devices from one 50 amp is not good. What is good is upgrading to the 50 amp breaker to power a sub panel from which you can have a 30 and amp breaker to power the AC and shower. Will need 6 gauge wire/cable from the breaker to sub panel
    – crip659
    Commented Mar 24 at 15:35

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You can't just add the circuit values together to put in a bigger breaker. That's a general rule, and there are certain very specific exceptions (e.g., with multiple cooking appliances).

But in any case you can't do this because all of the wire must be appropriate for the breaker size. The breaker protects the equipment but first and foremost it protects the wire. For a 50A breaker, the wire needs to be either 6 AWG or 8 AWG, depending on wire/cable type. See an ampacity table for details. 10 AWG and 12 AWG are simply not allowed on a normal 50A circuit.

In addition, replace the 30A GFCI with a 50A GFCI is going to be as expensive, if not more expensive, than adding a 20A GFCI. If your steam shower is actually a 120V circuit then a 20A GFCI is much less expensive and doesn't even have to be a GFCI/breaker, which will save even more.

In any case, the correct solution is to add a new 20A 12 AWG circuit and not touch the 30A circuit.

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    Appreciate the help! I have a sub panel in my garage that I still have room to to add a breaker. Will install 20 amp double pole breaker and do a run with the correct wire size from there as it is roughly only 30 feet away and easily accessible.
    – Mtuvey
    Commented Mar 24 at 20:57

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