Electric Furnace Wiring

This week I found the electric furnace wiring was not your typical wiring. Typically you have two breakers at the furnace with two service wires, one for each breaker. This one had one service wire connected to an 80 amp breaker in the main panel with one leg on each breaker with 30 amp jumper wires feeding the other terminals. The main service cables were puling about 66 amps and the 30 amp jumper wires were pulling 40 amps. This furnace has been in service for 16 years. I just scratched my head and requested an electrician look at it.


Good catch. Let us know if you hear what the electrician had to say.

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The more I think about this it makes me wonder if that was an (poor) attempt to be sure both breakers trip in unison??

Looks like you have a 15kw furnace, what brand was it? The 66amp is total load across both breakers and their loads. One breaker is pulling 40amps (2 strips), the other 26amps (1strip + blower). They used a single supply breaker to feed the furnace, this can be fine if done correctly. Continuous loads need to be derated. The OCPD needs to be sized 125% of continuous load. So the 80amp [can normally carry 64amps of cont. load] breaker may or may not be okay, need to check the manual. The way they wired the jumper wires is questionable because of the breaker terminal rating for a single conductor. They make a specific kit for this that looks like this: