Quote:
Originally Posted by schwarz633
While 12AWG is rated at 20A, you are only allowed to use 80% of that (16A). Your 10AWG is rated at 30A, 80% is 24A. Protecting the 10AWG wire with a 20A CB is allowed, you can always put in a 30A CB if it starts tripping.
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Expanding on this a little. I found out from our electricians at work is you should only run the breaker at 80% as well. Running higher than that shortens the life of the breaker, worst case it won't trip when it needs to.
We had a 100a 3 phase running in the low 90's. Running a row of racks in a data center. We had to get creative and feed a couple of the racks from another source.
TL;DR, if you have 10g wire, and the heater does consistently draw 20a when running, use a 30a breaker. Just because it says 20a on the label doesn't mean it actually pulls 20a.