furnace connection


Old 10-08-00, 02:16 PM
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i am trying to connect a furnace. it is an electrical furnace. however it was previous
jerryrigged with an extension cord(very bad),
but it worked. there are no boxes on the furnace. i figure that a couple of old work
boxes with a 1/2" niplle will work. i have to run power to the furnace and to the thermostat. will that work or should i us e another size box. also will ac cable work to hook up thermostat.
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Old 10-08-00, 03:05 PM
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Most electric furnaces have overcurrent devices [breakers] built into the furnace this is to protect from overcurrent and also detect excess heat in the furnace. If you don't have these then I would install a breaker box on the furnace with these breakers. Most heat banks are split with half of the elements on one double pole breaker and the other half on another double pole breaker. Usually these electric furnaces are run on two separate cables feeding the same furnace. We would need to know the kw ratings of each circuit to be able to tell you the wire size required to feed these heat banks.

Now as for your thermostat. The thermostat is usually powered off one of the feeders to the furnace through a low voltage transformer usually 24 volts transformer. The low voltage would wire the grounded conductor straight to a high voltage 4 pole relay capable of carrying all the heat banks or two 2 pole relays capable of carrying 1/2 and 1/2 of the heat banks. When the thermostat closes calling for heat then the thermostat merc switch closes and completes the power circuit to the magnetic coils of the one or two relays pulling in the contacts and energizing the heat banks. Don't forget to run a high limit thermostatic switch in the furnace and route the power going to those magnetic coils pulling in the contactor points through that high limit switch. Set the high limit switch around 200 degrees. This way the furnace will be protected from over heating. Also you will have to create another low voltage power from the 24 volt transformer to another thermo disc rated about 150 to 175 degrees to the magnetic coil operating a 20 amp contactor designed to operate the fan on that furnace.

Hope this helps but be safe


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