I'm wiring a steam generator for my shower and I'm not sure of what I'll need. Here are the specs:



AMPS : 48


Run 240V Power source to the generator

Wire sizes recommended by NEC (2002 Version). Minimum wire temperature rating 90°C. Type THHN.

Does that add up to needed a 60amp double pole breaker to deliver 240 volts with a 4 AGW wire? I assume 60 amp breaker since the machine uses 48 amps and you can only use up to 80% of the capacity.

  • 3
    Sounds right, but check the cost with 2 gauge aluminum if it will fit in the breaker. Might be cheaper than copper depending on distance. Think you might be able to use the minimum of 6 gauge copper/4 gauge AL also, but bigger is usually better.
    – crip659
    Jan 18, 2023 at 22:11
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    Read the installation instructions, don't just do a simple calculation based on your understanding. For example, our GE range is rated 10.0 kW at 208 V and 13.3 kW at 240 V, but the installation instructions recommend/allow a 40 A double pole breaker. The required breaker for your bathroom "steam generator" might not be based on a simple calculation of derated maximum power. I find it hard to believe that any consumer appliance like that would require a 60 A breaker. Jan 19, 2023 at 1:19
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    @Jim ranges are weird, though, they heavily consider demand factors. (all burners won't be at 100% duty cycle all the time). Heaters on the other hand take a 125% derate. Jan 19, 2023 at 1:20
  • @Harper, yeah nobody has all 4 surface burners on max and the oven on high broil at the same time, but a "bathroom steam generator" might pull full power continuously. What do the the instructions say? Jan 19, 2023 at 1:25
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    THHN wire is individual wire that meets a certain standard of being rated to operate at up to 90 deg C. in dry locations and is used in conduit. It sounds like the instructions are assuming that the wires supplying power to this device will be in conduit rather than NM cable. Jan 19, 2023 at 4:28

1 Answer 1


Certain loads including heaters require a 125% derate, so take 48A and multiply by 125%. That will give 60A right on the button. This builder knew what they were doing. You need an actual 60A circuit.

An actual 60A circuit requires:

  • 4 AWG Type NM or UF cable
  • 6 AWG "any other type" copper wire or cable if the terminals are rated 75°C
  • 4 AWG "any other type" aluminum wire or cable if 75°C and rated for aluminum

This is not to be confused with a 55A circuit using #6 NM/UF cable. That circuit is allowed to use a 60A breaker because 55A breakers are not made, but that is still a 55A circuit and inadequate for a 60A provisioning (48A heater).

  • Given the machine is using 48 amps, is there a benefit to use 4 gauge instead of 6? Jan 21, 2023 at 1:36
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    @AfterWorkGuinness There's an advantage to larger wire if you're going a long distance, but if you are, then find a place for a subpanel nearby and run 2-2-2-4 aluminum to the subpanel. Huge savings and nothing wrong with it as subpanel feeder. If you're using NM or UF, one advantage of #4 is the inspector won't red-flag it and make you tear it out. LOL. Jan 21, 2023 at 8:19
  • Thanks for the tip. Finally got hold of the inspector and they said #6 was fine for this application. Jan 23, 2023 at 14:31

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