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Old 12-26-2012, 11:07 PM   #1
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wiring 240v wall heater


Hi, we just bought a 240v wall heater. My question is this; The heater has a black and a red wire. Our wall wire from the breaker box has a red, black,
white and a ground. It was originally wired to have an external wall thermostat but we ended up buying a heater without that. So, what do we wire to what and what should we do with the extra wire? Thanks!

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Old 12-26-2012, 11:12 PM   #2
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wiring 240v wall heater


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Originally Posted by manda View Post
Hi, we just bought a 240v wall heater. My question is this; The heater has a black and a red wire. Our wall wire from the breaker box has a red, black,
white and a ground. It was originally wired to have an external wall thermostat but we ended up buying a heater without that. So, what do we wire to what and what should we do with the extra wire? Thanks!
Ground the bare conductor to the heater cap off the white and all you have is black and red left...

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Old 12-26-2012, 11:29 PM   #3
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wiring 240v wall heater


ok, did that and nothing happened when we turned it on....
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Old 12-27-2012, 12:16 AM   #4
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wiring 240v wall heater


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ok, did that and nothing happened when we turned it on....
Manda-

First thing to do is to check and see if you have the proper voltage at the outlet, i.e. point of attachment for the heater. You should see 120VAC black to white and 240VAC red to black (I am assuming that you have a means to check voltage and understand how to do it). This assumes that the installer ran this cable in anticipation of this use. Assuming that he/she did, the circuit in question should be fed from a double-breaker which is handle-tied (i.e. one handle that operates both breakers). If it is present in your panel (and labelled), make sure that it is on.

We'll go from here
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Old 12-27-2012, 12:23 AM   #5
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wiring 240v wall heater


You said the old one had a wall thermostat. Is that still installed? If so, it may be in series with the heater. You would need to remove it and connect the old thermostat wires together to make it work. Or just turn the thermostat up!
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Old 12-27-2012, 12:27 AM   #6
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White = neutral
Black = hot leg #1
Red = hot leg #2
Leg #1 and #2 is 240 volts.
any leg to neutral or ground(never do this) is 120v

So what you want is black to red. Make sure at the panel those two wires lead to the breaker. It will be a double. Also ensure the breaker is getting 240 volts on the two screws. Be careful when playing in there live. What I'd do is turn off the main, remove the cover, turn the main back on, and test the breaker. Turn the main back off before you do anything else.

You may have to move it over. Normally the bus bars alternate but I noticed in my panel there's a few spots where it does not. Maybe yours is the same way. With a few breakers removed you can see how the bus bar "zig zags" and there are two separate ones. You want the breaker to be on an area where it touches both bus bars. I hope this makes sense.

In this case you don't need the white but it does not hurt to still make sure it's connected to the neutral bus bar at the panel while you're in there, but you don't have to.
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Old 12-27-2012, 07:16 AM   #7
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wiring 240v wall heater


What does a wall thermostat have to do with running a 3-wire? This is not at all necessary, it's still a straight 240V appliance. Neither the thermostat nor the heater require a neutral.

If you hook up black to black, red to red, and cap off the white it should work fine. If it doesn't you have a problem elsewhere. Are the black and red on the breaker?
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Old 12-27-2012, 08:01 AM   #8
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Is the heater on a 2 pole breaker?
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Old 12-27-2012, 08:27 AM   #9
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Is the heater on a 2 pole breaker?
That was my thought as well. Also don't understand why the existing cable is 3-wire. Wonder what used to be powered from that circuit?
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Old 12-27-2012, 08:29 AM   #10
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wiring 240v wall heater


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Originally Posted by Red Squirrel
any leg to neutral or ground(never do this) is 120v
Why do you submit the "never do this" statement?
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Old 12-27-2012, 08:41 AM   #11
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wiring 240v wall heater


Since the old unit was controlled by thermostat I believe your problem is probably with the wiring at the stat. Please tell us what you did with wires at the stat.
Also do you have a meter? Can you measure for voltage. Maybe the last person did no use the red and black. They could have used the black white or red and white.
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Old 12-27-2012, 10:27 AM   #12
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Wow, thanks for all the advice! I'm at the job I actually know how to do but will go back to being an amateur electrician tonight. I will check the box and where everything connects. This is a new apartment with all new wire that was strung for a 240v heater and they put a thermostat mount next to it but we ended up buying a heater off Craigslist (brand new) that doesn't use one. The wire is wired to two breaker switches and I'm thinking the red and white are hot (120 each) to make 240? We tried capping the white and just hooking up the red/black and ground and nothing happened when we flipped the breaker and turned it on.
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Old 12-27-2012, 10:53 AM   #13
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wiring 240v wall heater


Best thing would be to see how it's connected at the thermostat box and the breaker panel. Red and Black should be hot white should be neutral and bare/green should be ground. But who knows how they wired it or if they were not done they may have left the wires in the breaker panel not connected. I do that to prevent someone from turning the circuit on.
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Old 12-27-2012, 11:12 AM   #14
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wiring 240v wall heater


This may help figure out what wires do what.

Disconnect all of the wires from the heater. Then measure voltage between every combination of two wires (red and black, red and white, etc.) both with the thermostat turned all the way down and turned all the way up.

Connect the heater red and black wires to the two wires in the wall cable with 240 volts between them.

If the wall thermostat does control those wires, you will probably get more even room temperature if you use the wall thermostat to control the heater and leave the heater's built in thermostat somewhat above the desired room temperature.
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Old 12-27-2012, 11:40 AM   #15
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wiring 240v wall heater


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