Yikes! Heater Power Cable Fried

[DaveR]

Everything was working great for a month then no heat. I checked the breakers no trips then when I opened the equipment door I could smell burnt wires.

Heater wires plugged into the relays were fried.

Questions

1. Why didn't a breaker trip
   
2. Any ideas what may have caused this
   

I plan to replace the relays and the heater including new thermisters. I don't want to spend $300 just to have it happen again. I'm thinking about disecting the heater before I put everything back together.

1997 HS Grandee

New tri-x filters cleaned weekly

Circ pump was working

The heater was replaced at one time, it was a newer version than the original.

[ed3553]

Generally this happens because the terminals on the heater power cord were not a tight fit. This will cause the wires to heat up and melt the outer coating. It could also be the contactors were worn and not make a good connection which would cause heat. If the heater is still functioning there is no need to replace it. Cut the burnt wire off replace the terminals and you can reuse the heater. Just make sure you push connectors fit tight on the contactor.

[Dr. Spa]

While the relays may have been fried, if there was no short the breaker wouldn't trip.

As ed said, a loose connection could cause the wires to heat up. Also any corrosion at a connection point could cause the same. Anything that restricts the flow of electricity will create a kind of heater and heat up the wire.

One thing to keep in mind with regards to cutting out the bad wire...heating the wires causes them to become restrictive to electricity. If you don't cut out enough, they'll just melt again. My understood rule of thumb is to cut at least 6" beyond any discoloration of the wires (NOT the insulation, but the actual metal of the wire)

[DaveR]

While the relays may have been fried, if there was no short the breaker wouldn't trip.

As ed said, a loose connection could cause the wires to heat up. Also any corrosion at a connection point could cause the same. Anything that restricts the flow of electricity will create a kind of heater and heat up the wire.

One thing to keep in mind with regards to cutting out the bad wire...heating the wires causes them to become restrictive to electricity. If you don't cut out enough, they'll just melt again. My understood rule of thumb is to cut at least 6" beyond any discoloration of the wires (NOT the insulation, but the actual metal of the wire)

Thanks,

I am going to give this a try. The terminals all need to be cleaned too.

If the heater starts to work I'll let it run a while and check the wires with infa-red thermometer to see if they are getting hot before I close everything back up.

Dave