Question about hookup of electric furnace

cwatkinJuly 16, 2011

I recently purchased a new place and it was cold outside when I moved in so I ran the heat for about a week before it got warm and it was no longer needed. This electric furnace runs off of 2x 60 amp breakers. One of these breakers tripped several times while I was using it and I decided to turn them both to the off position and deal with this problem as a summer project.

Now that is it hot outside and I am using the AC, I decided to tear into this project while doing some other basic wiring. Well, I opened the breaker box and removed the breaker for the suspect circuit only to find that the two hot wires were not clamped down by the two screws that attach them to the breaker. The breaker came completely out in my hand and was basically not attached. I noticed that the copper wiring was discolored from the arcing and the insulation on the white wire was turning brown from the heat so I assume this is why this breaker was tripping. I replaced the breaker and screwed it down correctly this time. I also checked the others and they were all tight.

I have two questions now. 1) Is there any damage this could have done? Is the wiring or any part of the furnace suspect from this error? 2) The wire is 6-2 with ground. The ground is much smaller and is probably a #12 or #10 at largest. The ground appears to be run as the neutral and this concerns me. I am not an expert at this and it may be ok but the problem with the breaker installation makes me concerned that the person who hooked this up wasn't doing things by the book. Is this ok?



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1. You've probably found all the damage. Make sure you cut the wire back to a point where there was no discoloring of the insulation. Also, examine the busbars where the breaker was plugged in for damage which will be indicated by discoloring, black marks and possibly pitting. Chances are, this breaker only fed part of the heating elements and not the blower motor or controls, If that was the case, damage to the furnace is unlikely.

2. The equipment ground is probably a #10, and that would be the minimum required size for a 60 amp breaker. Neutrals are typically not needed on this type of equipment, so your equipment ground is not being used as a neutral.

I'm sure that by now you've checked the connection on the other 60 amp breaker and all the connections at the furnace.

    Bookmark   July 17, 2011 at 9:41AM
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It sounds like the furnace was connected with the wrong breakers in the first place. 220V circuits must have both legs disconnect simultaneously.
You need to replace the two 60A single-pole breakers with a 60A double-pole, or otherwise tie the two breakers together so they trip at the same time.

    Bookmark   July 20, 2011 at 10:53AM
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I think you fixed the problem

Randy It is probably a air handler with a 20kw strip package which would be 2 60amp double pole breakers of which one will usually run the blower motor and 10kw of strips and the other breaker will operate the other 10kw strip package

Cwatkin.. I would also look into 'staging' the strips with a good thermostat especially if you have a heat pump. On a heat pump it will save a bunch of money. I can explain in further detail if needed either here or post a message in the heating and air side if I dont' catch it in here.

    Bookmark   July 20, 2011 at 11:55PM
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electric furnace has two 60 amp two pole brks.15kw heat strips.
one 60 has two wires from the load side each pole ( four total). the other 60 brk has one wire on the load side on each pole (two total). There is a 2# awg
alum off a 100 amp brk in panel to one 60 and jumper 10# awg
to the other 60 brk. I think it should be a sept circuit, 10# awg
with a 30 amp brk. in the panel to the 60 amp brk. that has total
of two wires on the load side and a 60 amp brk in panel to the other 60 amp brk that has total of four wires on the load side.
I think this is the right way.wright or wrong?

    Bookmark   May 19, 2013 at 8:56PM
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