I bought my house new in 1978 with forced air electric heat and in all that time all the maintenance required has been to oil the blower motor a couple of times and I periodically have to replace failed sequencers (time delay relays) when I notice the vent temp is getting low from not all elements being powered. I have a 7.5Kw generator for backup power but my 23Kw furnace has always been beyond reach, of course.
I ordered new sequencers and while waiting for them I studied the schematics. My furnace is fed by 3 separate 240 volt circuits to three internal breakers 60A, 50A and 15A. The 60A fed the transformer, the blower and two 5Kw elements. The 50A fed two more 5Kw elements and the 15A fed the remaining 3Kw element. I wanted to be able to power one 5Kw element with the generator but the 15A breaker was insufficient for that. Luckily, that breaker was fed by a 30A breaker in my service panel over 10 gauge copper wire. I was able to find a 30A replacement breaker for the furnace and installed it.
I rearranged the wiring so that now the new 30A breaker carries the blower, transformer and one 5Kw element while the 60A one has two 5Kw elements on it and the 50A one has one 5Kw plus the 3Kw element. The bottom line is that with the two large breakers turned off the furnace will operate completely normally but with only 5Kw capacity. I tested it out and I was getting at least a 10 degree F. rise in the vent output air compared to the inlet. Winter temperatures here near Seattle seldom dip below the 30s (F) so it could actually work. I think it will be enough to keep the house livable if we have a power outage during cold weather but I hope to never find out! Still, I'm very pleased with myself for doing this modification.
Rob
I ordered new sequencers and while waiting for them I studied the schematics. My furnace is fed by 3 separate 240 volt circuits to three internal breakers 60A, 50A and 15A. The 60A fed the transformer, the blower and two 5Kw elements. The 50A fed two more 5Kw elements and the 15A fed the remaining 3Kw element. I wanted to be able to power one 5Kw element with the generator but the 15A breaker was insufficient for that. Luckily, that breaker was fed by a 30A breaker in my service panel over 10 gauge copper wire. I was able to find a 30A replacement breaker for the furnace and installed it.
I rearranged the wiring so that now the new 30A breaker carries the blower, transformer and one 5Kw element while the 60A one has two 5Kw elements on it and the 50A one has one 5Kw plus the 3Kw element. The bottom line is that with the two large breakers turned off the furnace will operate completely normally but with only 5Kw capacity. I tested it out and I was getting at least a 10 degree F. rise in the vent output air compared to the inlet. Winter temperatures here near Seattle seldom dip below the 30s (F) so it could actually work. I think it will be enough to keep the house livable if we have a power outage during cold weather but I hope to never find out! Still, I'm very pleased with myself for doing this modification.
Rob
