# Help with baseboard heater relay



## carmusic (Oct 11, 2011)

since they are on different breakers it is not recommend to do that (you would need 2 relays). how many watt are the heaters, can you join them on the same 20A circuit?
best solution is to get rid of all relays, put them on same circuit and use a regular line voltage tsat but this mean a lot of rewiring


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## 98mrd (Dec 23, 2011)

That's not a possible solution. I would need almost 40 amps - that's why they are on two circuits. I'm in no way connecting the two circuits together. They are kept isolated at all times. The relay on there now is designed to control two circuits. Two separate electromagnets are activated which turns on both circuits - they don't connect at all.

Even 10 gauge wire would be insufficient for the amperage. If you start at 30 amps, subtract 20% since they run continually, you are at 24 amps, which is nowhere enough - also it's about 100 feet from the panel, so there is some loss to that too.

I have to preserve the two separate circuits, I just need to find another relay that runs two circuits at the same time, or possibly alter this relay by replacing the transformer to increase the current.

See the wiring diagram here: http://www.platt.com/CutSheets/White-Rodgers/24a06g-1 Instal.pdf

EDIT: BTW, a licensed electrician installed the existing relay. It is up to code - the issue is that it only supports a 2-wire 24V thermostat.


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## carmusic (Oct 11, 2011)

you have over 4800w of baseboard heaters in one room :huh:


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## darren (Nov 25, 2005)

You have to use a 2 wire thermostat. Why would a thermostat have 3 wires?. Line voltage stats are either 2 wire or 4 wire.


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## 98mrd (Dec 23, 2011)

I have around 8000W for that room (2 2000W 50inch dimplex linear convectors on each wall - 4 total) - and that's barely enough to heat it when it gets cold. The room is large and has cathedral ceilings too.

It's not a line voltage thermostat... it's a 24V thermostat. That's the point of the relay. It controls two 20 amp circuits with a 24V thermostat. It has always been different from the rest of the house (for 40 yrs now) because no single circuit / line voltage thermostat could be used (other than something very industrial I suppose).

The two wire 24V thermostats are the old mechanical ones - that's what I just replaced. The third wire is a neutral so that the digital thermostats can be powered and light up the LCD.


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## joed (Mar 13, 2005)

> except that the transformer can't generate sufficient current to power the tstat


Simple. Get a bigger transformer.


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## Missouri Bound (Apr 9, 2011)

Take the thermostat out of the circuit and short the wires. See if that operates the relay. It's hard to believe that the thermostat would need more than the relay to operate. It's almost always the other way around. And when you modified the relay, you took away it's UL listing....just sayin'. Where did you get the neutral from anyway? From looking at the schematics it looks as if the relay is intended to work off a mechanical tstat. Have you checked the voltage that the xformer is putting out. Just because it says you can use a 24v thermostat doesn' mean it's a 24v output. Just some things to think about.


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## a7ecorsair (Jun 1, 2010)

98mrd said:


> I'm looking for a new relay that will control 2 240V 20A circuits off one 24V 3-wire tstat. Does anyone know of such a product? Alternatively, anyone have any advice on another way to solve this problem?
> 
> Thanks in advance.


Your relay is designed to support two 240 volt loads at 25 amps each.
The relay requires .2 amps at 24 volts
Have you already bought this three wire t-stat? what is the brand and model?


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## 98mrd (Dec 23, 2011)

Disconnecting the thermostat and shorting the red to white activates all the heaters. You can observe the relay functioning (it's electromechanical) and both electromagnets power on and close the switches activating the 240V circuits.

Removing and replacing the transformer is possible, assuming I could obtain one with the proper ratings (not sure what that would be - I can't find detailed specs). It also increases the risk of potentially running too much current over the small tstat wires.

I know I too away the UL listing - and ideally, I'd just like to get a new relay that would do the job. I can't be the only person ever to encounter this issue.

The voltage has always been under 24V. I've checked it with a multimeter and it's around 21.5V AC. I'm not sure why this is. However, it functions fine at that voltage normally (it's the same when the thermostat is not hooked up, and in the original configuration, and it doesn't seem to affect the thermostat running, so I think it's unlikely that is the issue).

I have already bought and hooked up the tstat, and I'm using it now - it provides some heat (half the heaters go on). It works fine aside from its inability to get the second circuit on. The thermostat is a Honeywell/Aube TH115-A-024T.

I got the neutral from the other side of the transformer. I just wanted a 24V circuit to power the tstat - I already had a lead from one side of the transformer. I needed one from the other side (but before it gets to the relay switches).


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## a7ecorsair (Jun 1, 2010)

Are there separate connections for the two coils on the relay? They need to be connected in parallel. 
You should not, can not, have a neutral from the primary side of the transformer connected to the t-stat. The t-stat operates on a transformer isolated 24v class two wiring. Your transformer may be connected to 120 vAC instead of the 240 as shown in the manual for the t-stat in which case you will have separate 240 wiring to the baseboard.
This is from your operator's manual.


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## Missouri Bound (Apr 9, 2011)

Which tstat are you using? You may be able to add a seperate xformer for thermostat power, and still use the internal xformer for switching the relay.


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## Speedy Petey (Feb 1, 2004)

Can you tell me what a "3-wire thermostat" is??? 

Every lo-volt t-stat I have ever seen was able to be used as a heat-only stat requiring only R&W.

You CAN use those 2-circuit WR relays with one t-stat.


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## joed (Mar 13, 2005)

> Removing and replacing the transformer is possible, assuming I could obtain one with the proper ratings (not sure what that would be - I can't find detailed specs). It also increases the risk of potentially running too much current over the small tstat wires.


The stat will use what it needs for current. The transformer is not part of the equation. It does not control current flow unless it is too small for the application and is being overloaded.


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## 98mrd (Dec 23, 2011)

Good points a7 - but don't worry. Yes, there are separate connections for each of the two circuits. The operators manual for the tstat shows a different relay (probably one of the aubes) that doesn't control 2 circuits. This one has lugs clearly marked for circuit 1 and circuit 2 by the manufacturer. Also - regarding the side of the transformer, I should have been more specific. I am completing a circuit which goes from transformer to tstat back to transformer - without having to pass through the electromagnets that would activate the heaters - but ALL on the secondary side of the transformer and all in he 24V wiring section. I've also tested it with the multimeter and it's getting a bit under 22V on that line. You are completely correct that connecting somehow over to the primary side would be dangerous and a bad idea (and I'm guessing would blow the t-stat, since it would be one of the 120V hots from the panel). That isn't the issue here. It's also part of why I was willing to tinker as much as I did. I knew it was only limited current 24V wiring that I was modifying on the 2ndary side.

Can I get two regular, single circuit relays and connect in parallel? What would the wiring diagram look like? That might be a solution. I'm not averse to spending a few bucks - I just want it to work.

As for the 120 vs 240, both baseboards are 240V, and the relay interrupts one leg of each (hence the reason the old thermostat was a SPST mechanical honeywell - one leg was always energized). There are a total of 4 lugs, 2 per circuit. It's like a switch just opening or closing one of the 2 hots on each 240V - so it would be 120V vs ground/neutral. When the tstat is off, they test as 240V (the return path is ultimately to the other hot on the bus). They both get 240V as wired.

Missouri - see above for the exact tstat model number. a7 also pulled from the manual.

Speedy - The tstat clearly states that it requires 3 wires. This is true of thermostats that have display screens and do not use batteries as a general rule. To complete the circuit and draw power, they need to return power, but with a 2 wire the only return passes current over the magnets and activates the relay. I added a neutral return wire between the transformer and the magnets so that the thermostat could draw some power and still not activate the heaters (to run the display, etc.)

joed - I agree with everything you are saying. My working hypothesis at this time is in fact that the transformer is too small and is overloaded right now. The tstat is pulling what it needs (just as when you plug in a nightlight it doesn't try to pull 15 amps on the circuit, it's ohms law, resistance, etc. - I get that). I think the transformer is overloaded though and can no longer supply enough power to activate both electromagnets and the tstat simultaneously.


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## a7ecorsair (Jun 1, 2010)

You will need a definite purpose contactor similar to this:
http://www.grainger.com/Grainger/SQUARE-D-Compact-Contactor-5B124?Pid=search
You are controlling only one leg to each heater using the same t-stat so each leg gets connected to one of the poles. 
You may still need a larger transformer. Hard to say.
The use of the term neutral was confusing. You need to power the t-stat as in the diagram which I thing you have done.


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## regularguy (Feb 16, 2010)

98mrd said:


> Hi - just joined the forum. I have been trying to figure out a problem for a while now and decided to (finally) ask for help.
> 
> My house is heated with baseboard heating. It was built in 1971. I recently replaced all the heaters with dimplex linear convectors and all the thermostats with honeywell digital programmable line voltage thermostats.
> 
> ...


I have the same setup. Do you have the instruction book for the 24A06G-1? If not you can get it here http://www.emersonclimate.com/Documents/White-Rodgers/instruction_sheets/0037-4165.pdf

This unit also works with heating and cooling, so one coil is for heat and the other for cooling, it can be set up that way, I don't use mine that way and I don't think you did either, but if it's not wired correctly it may think one relay is for cooling rather than both coils for heat, that could be why only one heater works. All of the 3 wire thermostats that I ever saw were for heat and cooling, can you wire it back the way that it was and just use 2 wires of the 3 wire thermostat?


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## 98mrd (Dec 23, 2011)

The two relays are in parallel - there is no difference between them really.

If I need a larger transformer, where could I get one? Any guess what specs I would need?


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## joed (Mar 13, 2005)

See if the one in there now has a VA rating on it. Go to electrical supply house and get one that is larger 10-20 %


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## regularguy (Feb 16, 2010)

98mrd said:


> The two relays are in parallel - there is no difference between them really.
> 
> If I need a larger transformer, where could I get one? Any guess what specs I would need?


Did you look at the instructions that I included in the earlier post? This relay can be wired in two different ways, I struggled when I did mine as I didn't read the instructions as close as I should have. That said if you are still confident that you need a larger transformer each bimetal heater uses .21 amps. Its in the instruction book


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## 98mrd (Dec 23, 2011)

I've checked the wiring - it's not wired for heater/cooler functions. The two heater circuits in the relay are completely parallel. If one is triggered, the other should be too. The path is the same.

I can't get to a VA rating on the transformer without removing it, and it's riveted to the metal box for the relay. Not trivial to reach, although I may end up doing it eventually.

However, if the two relay coils require .21A each, and the thermostat can only handle .5A, it leaves only .08A for the thermostat to run - I don't know what a typical 24V thermostat requires to run. Does anyone have any idea?

My other idea was to wire 2 Aube 3 wire RC840T's together. I'm not quite sure how to make the connection. Does anyone have an idea on this? I know it can be done - the web page claims that you can control multiple relays with one thermostat as they require only .04A per relay. It does not show how to wire two of them together. I'm guessing you only power the transformer on one of the two, then maybe run them in series? Any help here would be appreciated.

Here's the link to the Aube thermostat. Honeywell has a very annoying policy of refusing to discuss their products with homeowners - I'd need an electrician or HVAC license.

http://www.aubetech.com/products/produitsDetails.php?noProduit=42&noLangue=2
http://www.aubetech.com/manuel/2/RC840T.pdf


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