# Wiring low voltage thermostat on profusion electric heater



## user_12345a (Nov 23, 2014)

You have to check the amperage rating of the heater and make sure it falls below the rating of the relay, hopefully 20%+ lower than the rating.

You get a transformer with the same voltage rating, with the same or greater va rating.

It wires across R and C of that relay.



The thermostat you use uses two wires, R and W. Keep labels consistent.

Power passes through R, gets sent to W, goes back to relay and switches it. internally it's connected to common, completing the circuit.

Put a in line fuse holder in series with the wire going from the transformer to R. 

Divide the VA rating by the voltage to get the amperage of fuse you need. You want the fuse there to save the transformer from overloading.

You'll need a very low amp fuse, like 0.5 to 1.


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## beenthere (Oct 11, 2008)

Can't read the heater diagram, too low of a resolution, or pic size is too small.

What KW, or amp draw is the heater.

You don't need an additional low voltage transformer.


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## user_12345a (Nov 23, 2014)

my impression was that the heater does not have a transformer in it and uses line voltage stat.


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## beenthere (Oct 11, 2008)

user_12345a said:


> my impression was that the heater does not have a transformer in it and uses line voltage stat.


Now check out the relay he is going to use.


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## Saleen_21 (Sep 12, 2017)

Heater is 21 amps, it currently has built in thermostat but want to install an external programmable thermostat the Aube RC840T-240 is a 240v-24v relay designed to be used for this purpose where you can run a low voltage thermostat off it. Here is link to profusion heater https://hw.menardc.com/main/items/media/HEIND001/Install_Instruct/eh4604.pdf and to Aube relay https://s3.amazonaws.com/s3.supplyhouse.com/manuals/1318845442419/66403_PROD_FILE.pdf, I just need to know where to wire in this relay? Do I unwire and bypass thermostat or tie into existing thermostat but crank into full setting? Here is an example of a nest being used with Aube relay but not sure this diagram will work with all heaters


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## user_12345a (Nov 23, 2014)

Have you looked at line voltage programmables? they exist.

The relay would be put in place of a line volt t-stat. it would interrupt one of the 220v lines feeding heater.

having trouble loading the attached pics.


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## user_12345a (Nov 23, 2014)

beenthere said:


> Now check out the relay he is going to use.


oops.

"On/Off Switching Electric Heating Relay with Built-in 24 V Transformer"


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## Saleen_21 (Sep 12, 2017)

I’ve looked for line voltage thermostats but could not find one to handle 20+ amps nor is programmable


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## Saleen_21 (Sep 12, 2017)

Not sure these pics are any better but anyone willing to assist I can email if that would be suffice


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## user_12345a (Nov 23, 2014)

I believe you would use the relay to break one of the 240v lines feeding the heater.

The temperature control, what is that? just a switch? a t-stat?

that would have to be left on.

I'm leary of putting 21 amps consistently through that relay. the rating is an absolute maximum current it can switch.


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## jimn (Nov 13, 2010)

Wiring is pretty straight forward. I would put in a new junction box ahead of the the heater and mount the relay in that. Your 240 line runs into the junction box and you connect L1 and L2 as shown . Note that there are two connections to L2 . Take the output of the control (the load connections)and run to the L1 and L2 connections on the heater . I would leave the existing thermostat in place and just set to a high heat. Removing the thermostat or otherwise modifying the heater would void its UL rating and if there ever was a fire it could peak the interest of an insurance company. You are maxing our this relay and checking with manufacturers might not be a bad idea.


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## Saleen_21 (Sep 12, 2017)

Well first attempt tripped the breaker, going off these wiring diagrams that others have used with success, attached is my wiring diagram.


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## Saleen_21 (Sep 12, 2017)

Wiring diagram that someone posted shows L1 going straight to black wire on Aube relay, the L2 going to L2 on heater and the red and blue wire on the Aube relay, (all tied together), only thing I haven’t connected was ground??


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## user_12345a (Nov 23, 2014)

its sounds like you created a short.

Yes, l2 goes straight to heater.

L1 goes through the switch section of the relay.

the relay may also need l2 on another connection to run the transformer.

l1 vs l2, doesn't matter what u call them or which side you decide to switch with the transformer, both are hot.


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## Saleen_21 (Sep 12, 2017)

I guess I’m confused where they’ve wired the secondary side of heater to the red wire in relay, not sure where secondary side is being considered. Have L2 going to primary side of heater than “Secondary” side going back to relay??


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## user_12345a (Nov 23, 2014)

Use the diagram supplied by the relay manufacturer.

The relay needs both lines because it has an internal transformer, that needs 240v power to produce the control voltage.

Only one line is switched.


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## electraglide (Nov 24, 2017)

Saleen_21 said:


> Wiring diagram that someone posted shows L1 going straight to black wire on Aube relay, the L2 going to L2 on heater and the red and blue wire on the Aube relay, (all tied together), only thing I haven’t connected was ground??


From an electrical standpoint, one of the first conductors I terminate is the ground. It facilitates, typically, the short circuit functioning of the breaker/fuse.


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## electraglide (Nov 24, 2017)

Did you get it to 'Silent Operator' to work yet?


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## electraglide (Nov 24, 2017)

Your device, also referred to as a silent operator, is most commonly used when you're controlling multiple electric heaters, that are on separate circuits/breakers. The low voltage wiring going to a common area thermostat, controls the temperature of that area, by controlling multiple heaters that are wired on different circuits.

Now, if you're not controlling multiple heaters, on two circuits, you can always ditch this device. That is provided you can pull line voltage conductors to your Thermostat location.

An example would be having crawl space access, where the silent operator is traditionally located. Thermostats are mounted on inside walls, so typically there is no insulation if you need to fish the conductors up.

If your LV conductors are already there, I would say, stick with what you have.


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## beenthere (Oct 11, 2008)

Saleen_21 said:


> Wiring diagram that someone posted shows L1 going straight to black wire on Aube relay, the L2 going to L2 on heater and the red and blue wire on the Aube relay, (all tied together), only thing I haven’t connected was ground??


That is not what it shows.

It shows L1 going to black wire of relay.
Blue wire going to L2.
Red wire going to heater's L1

Heater's L2 also gets connected to L2.


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## Saleen_21 (Sep 12, 2017)

Finally got it to work by wiring it this way.
Incoming LV to black wire of relay
Incoming LV tied to blue wire of relay and to L2 of heater.
Red wire of relay to L1 of heater


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