Combination Bath Fan

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jmellc

Senior Member
Location
Durham, NC
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Facility Maintenance Tech. Licensed Electrician
Looked at a bath fan unit the other day. Fan, light, night light & heater combo unit. 4 switch leg feeds to unit. Done with separate 14/2's; cable 1 has common neutral to all, & black to fan. 2 has hot to light, white to night light, 3 has black to heater, white capped off. All grounds connected. 2 of the cables have been overheating; jackets discolored & partially melted. Same with main feed to switch. I see why switch leg cables may overheat, with no hot/neutral balance in cable. But feeder to switch is hot/neutral/ground & should have even load. Fan has been locking up a long time. I guess extended lock up could cause overheating but also should trip the breaker, a 15 amp sp breaker. It is a GE breaker though, maybe that is the problem. I will do an amp check when I go back there.

When I replace the unit I will wire with flex and THHN conductors.
 
is it a heater, or a heat lamp?
if its a heater then it probably needs to be on its own 20a supply, if not its probably causing the excessive heat in wire
 
What is the distance to the panel. Were the units plugged in tightly or could there have been a loose connection. I am assuming resistant heat.
 
Coil type heater, standard fan motor, light and night light.

I will use flex and THHN stranded to keep minimum needed conductors and stranded packs better in wiring boxes.

Some of the new combo units in stores specify 20 amp ckt. I will repull ckt in 12 and put on 20 amps.
 
Dennis, about 30 feet to panel. All connectors were tight. Fan had been the only issue; customer said it stopped working a year or so ago. Someone probably turned it on along with heater & didn't notice it humming the "lockup song", then turned it off with heater too.
 
I'll hazard a guess and say that the discolored ones are #1 (the common for all) and #3. Your culprit seems to be the heater, not sure how big of a heater it is, but 2000W is not uncommon and that will overload the wire. Why the breaker doesn't trip? I would hazard another guess that the discoloration occurs where all cables are close to each other(derating fail?). Also keep in mind that breakers are inverse proportional, meaning the lower the amps over, the longer it takes to trip. So in a situation where the derating wasn't taken in consideration, a 15A breaker will not trip at 17A for a good 20-30 minutes, but every time that 20-30 minutes occurs of 17A the temperature in certain spots will go above 90 degrees. And from there it's a vicious circle, the more they get cooked, the more they'll heat up next time.

jmellc said:
Looked at a bath fan unit the other day. Fan, light, night light & heater combo unit. 4 switch leg feeds to unit. Done with separate 14/2's; cable 1 has common neutral to all, & black to fan. 2 has hot to light, white to night light, 3 has black to heater, white capped off. All grounds connected. 2 of the cables have been overheating; jackets discolored & partially melted. Same with main feed to switch. I see why switch leg cables may overheat, with no hot/neutral balance in cable. But feeder to switch is hot/neutral/ground & should have even load. Fan has been locking up a long time. I guess extended lock up could cause overheating but also should trip the breaker, a 15 amp sp breaker. It is a GE breaker though, maybe that is the problem. I will do an amp check when I go back there.

When I replace the unit I will wire with flex and THHN conductors.
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