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Replacing Electric Heat Thermostat Question (Don't want to burn the house down)

Replacing Electric Heat Thermostat Question (Don't want to burn the house down)


Old 01-09-06, 08:51 AM
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Question Replacing Electric Heat Thermostat Question (Don't want to burn the house down)

Hi Folks,

Long time reader...first time poster...

It's a cold winter and running off electric heat is starting to hurt the wallet a bit. In an effort to try to save cost, I yesterday replaced my old (probably 30 year old) electrical baseboard heat thermostat with a new digital programmable honeywell thermostat (Model TH104...designed for electric baseboard heat).

The instructions had a '4 wire' wiring diagram (Power supply at the thermostat, and not at the heater). This appears to be what I have...but with a twist (I'll get to the twist in a minute). The thermostat has 2 black wires coming out of the back of it (no ground...which I thought was interesting). On the 4 wire wiring diagram, it showed the 2 white wires just being connected together in the box, and the 2 black wires (1 from the power and 1 out to the heater) being connected to the 2 black wires on the thermostat. Seemed pretty simple...although I'm still wondering why it doesn't have a ground.

Anyway, the twist is this...when I removed old thermostat, I saw 3 12/2 wires coming into the box (A bit different then the wiring diagram which only showed 2 12/2 wires). This is because the wall that the thermostat is on, is a common wall with the bathroom, which has a little 3 ft electric baseboard heater (built in thermostat) on it. So I assume that the 3 wires in the box correspond to:

1) The line coming from the power source/breaker box
2) The line going to the bathroom heater
3) The line going to the main living room heater (which is the heater on the thermostat).

So what I did was this:

1) I connected the power source line to the bathroom heater line (just connected white/white, black/black and ground/ground.
2) I then pig-tailed (I think that's the right term) a single 12 gauge 6 inch black wire onto the 2 other black wires (see #1).
3) I then connected the thermostat to that pig-tailed black wire (from #2) and to the black wire on the line going to the main living room heater.
4) I then connected the white wire (from the living room heater) to the other 2 white wires (from the power source line and the bathroom heater line), so the 3 were just connected.
5) I then connected the ground from the living room heater line to the other 2 grounds in the box (from the power source line and the bathroom heater line)
6) Wire nutted them all, pushed it back into the box and flipped on the breaker.

Everything seems to be working fine (both heaters work). The bathroom heater works find (regardless of whether the living room heater is on) and the living room heater seems to be working fine via the new thermostat.

However, I'm admittedly a pretty handy guy, however, I'm no electrical guru...so I just want to double check that this is a safe installation. It appears that I've connected this thing as close to the wiring diagram as possible...but the addition of the 2nd heater (bathroom) makes it just different enough to make me wonder.

Also, any idea as to why the thermostat doesn't have a ground? Does it not need one since it's only connected to the black wire (and not both the black and the white)? I would think this thermostat would be similar to a light switch (although a bit more complex)...which are always grounded.

Anyway...hopefully some bigger brains then mine and help put my mind to ease.

Thanks in advance!

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Old 01-09-06, 08:58 AM
Join Date: Sep 2003
Location: Central New York State
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You wired things properly. No ground is needed since the thermostat is all plastic. Light switches are grounded because they are made of metal.
Old 01-09-06, 09:04 AM
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Thanks a lot racraft...that's the reassurance I was looking for!
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