What guage wire?

[hermit]

I am planning to install a wall mount electric heater in my shop. Its 240v 4000w rated at 16.7 amps. I already have a 220 line with 12/2 hooked up to 20A breakers but not using. I was planning on using that for the power, until I read in the manual that they recommend 10 awg wire. Is that necessary with the rating on this unit, and if so, should I change the breakers to 30A or just switch the wire??

Todd

[Uncle Cracker]

You do not want to use 20A breakers on a 16.7A rated appliance. That much is certain. Whether you need to upsize the wiring, that might depend on the length you are dealing with from the breaker box to the appliance. I think it would pay you to err to the side of caution on this one.

[Hellrazor]

"As a general rule, the ampere rating of a fuse or a circuit breaker is selected at 125 percent of the continuous load current. Since the conductors are also typically selected at 125 percent of the continuous load current, the ampacity of the conductors is typically not exceeded. For instance, for a 40 A continuous load, the conductor must be rated to carry 50 amperes (125% of 40A) and a 50-ampere fuse or circuit breaker is the largest that should be used."

#12 is rated for 20A

16.7A x 125% = 20.875A

You can't use the #12 wire or the 20A breaker. Use #10 and a 30A breaker.

[hermit]

okee dokee,
thanks for the answers. That makes up my mind. You know I find it awfully funny how all the wiring inside the heater, including the 2 wires to connect to line, are all 14 guage. Of course they aren't single conductor, I guess that makes a difference.

Todd

[Uncle Cracker]

okee dokee,
thanks for the answers. That makes up my mind. You know I find it awfully funny how all the wiring inside the heater, including the 2 wires to connect to line, are all 14 guage. Of course they aren't single conductor, I guess that makes a difference.

Todd

Actually, that wire inside the heater does not run any length at all, so the "distance resistance" does not come into play. It's kind of like a one-foot run of pipe that's too small... It doesn't cause the same pressure loss that a hundred-foot run would. And don't forget, that heater is designed to heat up... You don't want the same thing happening in your walls or attic.

[hermit]

Update:

Thanks again for the feedback. Unit is all hooked up and works great. Ran the 10g with 30A breakers. Can't wait to see how it works in cold weather. Seems to throw a lot of heat.

Todd