OT 220 single phase heat treat furnace wiring

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Old 12-16-10, 05:31 PM
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OT 220 single phase heat treat furnace wiring

Iím having some issues with wiring a Heat Treat furnace. I picked up a new controller but am not sure what exactly I have or how it should be wired (furnace). It was taken from service before I acquired it and only has two wires coming from the conduit whip where it was connected to the previous service. The old analog controller was pretty much junk and I ďstraitĒ wired it thru the old controller by screwing the two line to leads together and it started to heat up. I had one hot each (110 volt) of my 220 going to the furnace without a common/neutral or ground. Is anyone familiar with how a furnace like this is to be properly wired in relation to the relay? Ought I have two relay switches or is there a better, standard way? I simply have no experience with this type of unit. Any advice sure would be appreciated. Earl.

Back side of the old controller, with the lines connected to give a strait feed.
 
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Old 12-16-10, 05:53 PM
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I think most electric heat treating furnaces today use solid state relays controlled by time-proportioning digital controllers. If you post some information about both the furnace (nameplate data) and the controller you have purchased someone might be able to give you a bit more information on how to proceed.

You don't need a neutral with your furnace (the controller might) but you do need an equipment ground.
 
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Old 12-16-10, 06:08 PM
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I'm sure you already know that your feed wires should be connected to the LINE terminals.

What are the two smaller wires going to the right in your picture? I would guess that would be your thermostat connection???
 
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Old 12-16-10, 10:49 PM
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Tolyn, Earl stated that he wired the power to the load terminals for testing purposes only. The two small smaller wires on the right go to a thermocouple for measuring the temperature in the furnace. I suspect that the thermocouple itself is missing.
 
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Old 12-17-10, 02:06 AM
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I think most electric heat treating furnaces today use solid state relays controlled by time-proportioning digital controllers.
Furd, This is what I plan to go to. I'm using an Omron controller and have purchased it and a PC interface with software package from a reputable dealer so I am good on it's instalation and programing. I just do not understand how my furnace needs to be "hard wired" to get it working properly. Running without a ground kinda scares me, so is it made to run with just two hots? And yes, those two small wires go to the thermocouple. Thanks for the response. Earl.
 
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Old 12-17-10, 07:50 AM
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Earl, the power comes just from the two hots on the line terminals. If that liquidtight conduit is the metal core type with metal fittings, then it can provide the ground. If not, it wouldn't be a bad idea to drill and tap a 10-32 screw into the metal frame on the controller and the furnace itself and run a #10 copper ground wire to the screws. The ground should run back to the panelboard or to a ground screw in a box where the conduit system is all metal back to the panel.
 
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Old 12-18-10, 04:47 AM
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ibpooks; Thanks for the reply, that is exactly what I wanted to know. I know little about 220 v wiring and it just seemed wierd not to have a return. Yes the conduit is metal armored but I can easily run a new ground wire thru it and have everything connected to the panel. Some of my planned carborizing soak cycles will go over 12 hours and I plan to use this alot over the next 30 years or so. Might as well put it in now to the best of my ability. Thanks to everyone. Earl.
 
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Old 12-18-10, 02:33 PM
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Just an FYI - The ground is not any type of return. It does not carry any current except during a fault. Your "return" is the other hot wire.
 
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