Wiring a programmable thermostat

[ourkid2000]

See the pics below....

I am replacing an older style electric baseboard (240V) thermostat with a newer programmable type.

When I took the new thermostat out, it only had two wires which kinda surprised me because my old one had 4 wires on it.

I used a multimeter to figure out what was going on with the wires. One black and one red (each have 120v on them) are wired to the old thermostat at L1 & L2 and the baseboard heater has a red & black attached to the pigtail off the T1 & T2 terminals. In addition, another heater (has it's own thermostat built into the heater itself) was wired into the red & black hot wires.

I'm not sure how to go about hooking up my 2 wire programmable thermostat to this. Anyone offer any help?

Thanks!

 

[LEVE]

I could be wrong (and I often am) but I don't think it will work. But more information is needed to know for sure. Can you post the type of the thermostat you bought, as well as any numbers, etc., of the one that is being replaced?

 

[ourkid2000]

The thermostat being replaced is a Honeywell & appears to be a double pole.

The programmable one is a Honeywell RLV4300A (designed for 240V electric baseboard heaters max 3000w).

 

[porcupine73]

Hm, if the new one is rated for 240VAC, a person might connect one (either the black or red) to one of the heater supply wires, then wire the thermostat in series with the remaining two wires (one supply and one heater). This is provided this heater does not have a neutral connection. This is not typically advised though, because generally you want to open all ungrounded conductors when turning on and off.

Maybe something like this, if thermostat is rated for 240VAC?
```characters ignore; they're just to keep spacing

----------red-----*--------red-----------
````````Supply`````````````Heater
240VAC split phase
````````Supply
----------black---|thermostat|--black----
````````````````````````````````Heater

 

[ourkid2000]

I think you're right yes.....

These heaters do not have a neutral connection and we're going from double pole to single pole. I didn't realize you could have one 120v hot straight to the heaters and have the remaining hot switched.

In this type of installation, are they using the bare copper wire as the ground for the circuit?

 

[porcupine73]

If the equipment needs to be grounded then yes it should be grounded. I would think it unsafe to not have it grounded because if a fault in the unit, ie insulation rubbing off one L1 or L2, could make the case hot without tripping the upstream breaker/fuse.

I'm not sure this method would meet code; often a switching means must open all ungrounded conductors (basically L1 _and_ L2). The neutral (which this circuit doesn't have) is normally not interrupted.

 

[ourkid2000]

So it uses the bare copper wire in place of the neutral?

 

[porcupine73]

I'm not sure what you mean. The ground and neutral conductors are separate conductors. No it should not use the ground as a neutral. The ground is not intended to carry current under normal operating conditions, whereas the neutral may.

If the heater is strictly 240VAC it probably doesn't have a neutral conductor because it doesn't need one. Unless it has a line to neutral 120VAC load such as a fan or something like that.

 

[ourkid2000]

Sorry, edit.....stupid question