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I recently purchased an indoor infrared sauna that pulls 18.3 amps I read that the max capacity for 14 gauge wiring is 17 amp on a 110 volt service Can I safely use a 20 AMP breaker with 14 gauge wiring for an appliance pulling 18.3 amps?

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No. No no no no no.

The sole purpose of the breaker is to protect the wiring from overheating. It's not just there to be a buzzkill. If you use a breaker that is too high for the wire you will lose that protection and there is a very real possibility of overheating and starting a fire.

An 18.3 amp device needs to be on a 20 amp circuit, meaning the receptacle, wiring, and breaker all need to be rated for 20 amps. (That would mean 12 gauge wire or bigger.) By the way, is your sauna really 120V? I thought most of them were 240V, which of course is a whole new thing.

  • What? Why would if make any difference if it were 120 or 240 volts? – Billy C. Jan 22 '16 at 22:29
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    @BillyC.: it sounds like he was trying to convert an existing 15 amp 120V circuit to use for the sauna, in which case he's probably short one conductor and definitely can't just replace a 15 amp breaker with a 20 amp one. I guess it's not clear exactly what he is proposing. You're correct that the amp rating of wire is not dependent on the voltage. – Hank Jan 22 '16 at 23:13
  • On what do you base the presumption that he could end up "short one conductor". Do you believe electric heaters need a neutral? – Billy C. Jan 23 '16 at 1:42
  • @BillyC.: I honestly don't know what his sauna requires for power. I wasn't trying to imply that 240V was impossible or even difficult, but it is a little different... different breaker size, different receptacles and plugs, and yes perhaps a 3rd conductor for neutral if the sauna has lights or controls. – Hank Jan 23 '16 at 2:00
  • The "No. No no no no no" comment above tells me all I need to know - I will have my electrician run a separate 12 gauge wire from my panel to my sauna – Brad Jan 23 '16 at 19:29
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The NEC provides the ampacities per wire size and type. A 14 can supply up to 15A, although it depends on the length of the wire and usage.

You should typically size your breakers to 125% of the load if it's going to be constant. In this case you'd want at least a 25A breaker and then appropriately sized wires and connections.

  • Uhm, which edition of the NEC is this from? It doesn't match up with the corresponding table in my copy... – ThreePhaseEel Jan 23 '16 at 1:36
  • my copy's of the 2014 NEC, and it lists that 14AWG 60degC copper is only good for 15A...o.O. Is there an erratum roaming around here, or was there a code change made on this recently? – ThreePhaseEel Jan 23 '16 at 1:44
  • Indeed -- the heading on the table in my copy refers to 310.104(A) instead of 310.13 -- I suspect the table you posted is from an older Code version?! – ThreePhaseEel Jan 23 '16 at 1:51
  • @TFK, just how are you figuring a 25A breaker for #12 in this case? – Speedy Petey Jan 23 '16 at 2:11
  • @TFK, you have to remember, there is a lot more to wire sizing than a simple chart. .... Even a 25A on #10 would not be legal in this case if the appliance has a 15 or 20A plug in it. – Speedy Petey Jan 23 '16 at 12:13

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