Hey Sparky's, Got an answer for me?

My question - why is a 30 ampere breaker with 10 AWG wire required to feed an electric water heater, when the wires in the heater itself are undoubtedly 12 AWG?

What am I not thinking of on this. Seems that it should be a 20 ampere breaker with 12 AWG wire or the water heater should have 10 AWG wire.

Thanks for your input.

The wiring inside of equipment has been approved and it likely is a higher temperature rating than regular house wiring.

It is a short run, serves as a fuse and will burn open if necessary all inside of a metal cabinet.

I had to run #6 to my airhandlers due to the heat strips installed and the wiring that I connected the #6 to inside the cabinet was a lot smaller too.

Hey John,

The manufacturers can get away with alot more than the Electricians who wire the units.

So lets say the unit has 4,500W

4,500W (divided by ) 240 Volts is 18.75 Amps so for the internal wiring it is fine…BUT we are bound by a higher standard…lol

Conductors - 18.75 x 125% = 23.43 amps…can’t use 12 AWG as it is only rated at 20A…have to to go to 10 AWG

Edit- Typo…lol…I have TONS of typos…lol


We are BOUND by our design my friend…

Just like the lamp you plug into the outlet that has #12 wire, and the lamp only has #16

Oh…and I forgot but for those who want to know why we put a 30A breaker on it…it is not because we can…lol…

Article 422.11(E)3 says that for applicances that are 13.3A a OCPD shall not exceed 150% of the appliance current rating.

IE: 18.75 x 150% = 28A so since no OCPD equals that the next size up rule applies and whamo…30A breaker…

Just in case anyone was wondering that…COURTESY of the POSSE’


Hey their Mark…What gave ya the “WOW” factor…lol

Electrician Side Note…I don’t care much for this image because the verbage as changed from the 2002 NEC to the 2005 NEC…while we are in the 2002 NEC here my verbage is correct…but the image is more catered to the 2005 NEC…

Basically the same…verbage different…the addition clarrification to allow minimum 125% rated of the OCPD but not the exceed the 150% rating as well…kinda don’t like how they re-wrote that …but who am I to tell the code panels how to write something…I am just a member of the POSSE’

FYI…yes you could put a waterheater on a 25A 2 pole breaker if you want…still has to be 10 AWG wire…anyway it is late and I am rambling now…Later

Outstanding info.

Thanks everyone. You just gotta love this site.

Glad to help John…

Actually JOHN…you should use a title like…“Electrical Masters and Rulers of the UNIVERSE” in the subject line versus…Hey Sparky’s…we are a sensative bunch…:slight_smile:

You also need to remember #12 is really good for 25a in 310.16. It is only 240.4(D) that has us thinking 20a. a 5500w water heater is only 23a or so. At the few feet a wire runs in a water heater this is negligible heating, where we are looking for heat in the first place.

Oh Greg…now you are PUSHING the envelope…thehehehe

Push it Baby…Push it !

FYI running the next size larger wire is a good idea for major draw appliances. You still have to fuse it correctly for the appliance though. It will save $$$ over time because of the lesser resistance of the wire. Motors will last longer, and the KWH on the meter will be a little bit less.:shock: :shock:

Yep…many times people size up the conductors simply to combat the voltage drop…very true…