60 Amp Electric Furnace
 

My cousin is installing a electric furnace which calls for 60 amp breaker to suppily it. The suppiler he bought the furnace from told him to use #6 copper so he bought 6-2 NM-B. will this do?

that depends on if the furnace needs a neutral or not.

What do the wiring instructions say you need?

I does not need a neutral. The hook up just has a 60 amp double pole breaker and a ground lug inside the furnace.

6-2 w/g

6-2 with ground NM-B is what he bought.

I disagree. #6 copper romex is only rated for 55 amps.
I would use #6 copper SEU cable. Rated 65 amps.

Seems I remember reading in the last code book something about sizing the wire for 125% of the load.

424.3(B)

An electric furnace is considered a continuous load.

Who calculated the load at over 55 amps?????

The mfg said 60 amp breaker.

Since 55 amps is not a common size fuse or breaker. A number six romex can be put on a 60 amp breaker.

So the furnace might pull 55 amps so they just call for a 60 so it can carry the load with out tripping?

another question is I was told by an electrician that a breaker is only good for 80% of the rating. so a 100 amp breaker is actually going to trip just over 80 amps. Is this true?

I think what you're recalling is that it's good practice to load a circuit to 80% capacity (ie, put ten 100 watt lights on a 15A breaker - 12A is 80% of 15A).

Jwhite, I don't understand the 55A explanation. If #6 romex has a rated ampacity of 55A, isn't it required that it's protected by an over current device no higher than 55A? I wouldn't think that the common availability of 60A breakers would be much concern to the NFPA. (But then, as I've proven in the past, I don't know a whole lot about this stuff.):)

Sorry, I still disagree. This is a contiuous load. Unless I calculate the load x 125%, and come up 55 amps or under, I will pull wire for the 60.

Who said it wasn't over 55. We dont have all the nameplate info.

This is a common red-tag around here.

Joseph, what does the nameplate say about the amperage?