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jreed 06-02-2010 08:14 AM

Electric Baseboard thermostat question
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I have purchased a new Honeywell RLV310A thermostat to replace the cheap dimplex that I have. The new has 2 black wires; the old has 4 wires, 2 red, 2 black. Out of the wall I have 2 sets of wires, each with a black, gray, and ground. I have attached a picture and a link to the wiring diagram for you to see everything.

If I read the schematic correctly, I need to connect the blacks to the new thermostat and wirenut the greys together? What am I to do with the grounds?

beenthere 06-02-2010 11:57 AM

Your local codes may not permit a single pole thermostat on your 240 volt heaters. May want to check before using those thermostats.

Ground connects to the thermostat on its grounding screw.

jreed 06-04-2010 10:26 AM

The thermostat doesnt have a grounding screw on it....what should I do in this case?

beenthere 06-04-2010 11:36 AM

Strange, since by UL requirement, I think it has to, to be UL approved.

Durt Ferguson 06-04-2010 11:46 AM

This may be a dumb question, but I was looking at the pdf and I don't understand the following :

1.) In the 2-wire diagram, black hot goes into thermostat, switched black wire comes out and is connected to neutral wire of baseboard. Black wire of baseboard goes to neutral to panel or rest of circuit. Why not hook black to black and neutral to neutral when wiring in the baseboard? Is this to denote which is hot and which is switched at the thermostat?
2.) In the 4-wire diagram. Why 2 black wires on the baseboard? Is this because it's basically a big non-directional resistor and it doesn't matter which end is hooked to hot and which is to neutral?

Sorry for the tangent.

Yoyizit 06-04-2010 11:55 AM


Originally Posted by Turd Ferguson (Post 451100)
Is this because it's basically a big non-directional resistor and it doesn't matter which end is hooked to hot and which is to neutral?

Electrically both diagrams are the same; a series circuit with stat, heater and power source.

The stat seems to be nondirectional [bilateral?] SPST switch
that probably uses a Triac instead of a MOSFET.

I'd think it drops one or two volts across itself when the stat switch is closed, to power itself. The clue is it needs more than "a resistive load under 2 A".
When the stat switch is open, there are probably some few mA drawn to maintain power. The electronics in the stat maybe needs several watts and the heat-sinked Triac may dissipate up to 1v(12.5A) = ~13w when the heater is on.

Apparently it doesn't need or use a ground so I guess it is double-insulated or no metallic parts are exposed to the user.

Durt Ferguson 06-04-2010 12:07 PM

I see what you're saying about the circuits both being the same, I agree, one just happens to have the neutral passing through the box and one doesn't. My question about which end was black/neutral and the non-directional resistor was in regards to the baseboard, not the thermostat (I should have specified better). If the baseboard can be hooked up any direction, that's fine, I just don't know why the manual for the thermostat would show black to white and white to black, it would seem to be clearer and safer for future maintenance to stick with the normal black is incoming power, white is neutral.

Yoyizit 06-04-2010 12:15 PM

I've seen that on dimmers, also.
Maybe this blk-blk color coding is an industry or UL custom? If it's blk you treat it as hot so you can't go wrong?

Durt Ferguson 06-04-2010 12:21 PM

Agreed, black may or may not be hot, better to play it safe. Even on dimmers though, the switched black wire from the dimmer would still go to the black on the light, not the white :huh:

beenthere 06-04-2010 02:04 PM

Is your baseboard 120 volt, or 240 volt?

mmonark 07-09-2010 04:09 PM

Did you figure out the answer?
Hi JReed -

I have the same exact issue you had/have. Did you figure out how to address the wiring issues and ground?


- Mike

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