Using thermostat with contactor/relay to control heater?

[AndrewRT]

So i have just recently installed a heater in my garage. The heater has built in heat control but it doesn't have a automatic shut off (which is what I want) so I also wired in a 2-pole switch. Now I have done some research to figure out how to control this heater with a thermostat and I found a couple ways, the first one is with a line voltage thermostat but I have had no luck finding one rated for 30Amps. Now the other method I found was with a contactor controlled by 24v circuit. I have drawn up diagram for both circuits (provided down below) and included a few more details of the supplies i'm using. I have several years of electrical experience and I know the essentials to residential wiring, i'm just not that familiar with installing contactors.
Basically to sum it up I want to ensure that I won't burn my house down.

My questions:
will this layout on my diagram function correctly?
Does it meet/violate standard code?
Does it pose any risks or hazards?
Does the contactor/relay require a specific enclosure or enclosure size?
Is the thermostat wired correctly?
Am I using the right Contactor?

The Contactor i'm using: https://www.amazon.ca/gp/product/B000H5WMXG/?tag=atomicindus04-20

Thanks,

 

[alfredeneuman]

Why run a separate 120V line for the control transformer?
If you take it from the 240V line then you'll be able to turn the entire unit off at once. (One off of an A/C unit would be perfect)
Either way, you'll need a fuse inline with the primary of the transformer.

As far as the Code questions, without knowing your location it's impossible to tell you

 

[matt_i]

The contactor with the screw terminals seems like a good idea. I have seen a similar one before (fuzzy, don't recall amperage nor brand) that only had the male spade lugs and I was not a big fan of attaching the power side wires in that manner.

I don't see anything that strikes me as dangerous or out of the ordinary there. Looks good

As far as your question about the contactor, biggest thing is being able to work inside the box comfortably. Usually the 4" sq and 4-11/16" sq are not deep enough so it forces you to go to a different (larger) enclosure that I would also bond to ground.

Many industrial enclosures use a backplane (flat piece of painted steel) which is spaced out from the actual rear of the enclosure by standoffs. That way the backplane can be either assembled offline and then installed into the enclosure, or else drilled and tapped in-situ without piercing the rear of the enclosure.

I would think that you could probably place the contactor and transformer (+ fuseblock as suggested) in an 8x8 enclosure with pretty good room to work.

 

[AntonLargiader]

Shutting the main power on and off to the heater can't be the best way. There has to be a control circuit somewhere that you can tap into.

What does the heater have for controls? I don't follow what you say about it having a heat control but not an automatic shutoff.

 

[AndrewRT]

Why run a separate 120V line for the control transformer?
If you take it from the 240V line then you'll be able to turn the entire unit off at once. (One off of an A/C unit would be perfect)
Either way, you'll need a fuse inline with the primary of the transformer.

As far as the Code questions, without knowing your location it's impossible to tell you

The heater draws 25amps and the circuit is 30amps but only 80% of that should be used, so im already 1amp over because 24amps is 80% of 30 and im using 25 for the heater. So i don't want to add to the load of the circuit with the transformer.

What do ou by "One off of an A/C unit would be perfect"?

I live in Alberta, Canada

 

[AndrewRT]

The contactor with the screw terminals seems like a good idea. I have seen a similar one before (fuzzy, don't recall amperage nor brand) that only had the male spade lugs and I was not a big fan of attaching the power side wires in that manner.

I don't see anything that strikes me as dangerous or out of the ordinary there. Looks good

As far as your question about the contactor, biggest thing is being able to work inside the box comfortably. Usually the 4" sq and 4-11/16" sq are not deep enough so it forces you to go to a different (larger) enclosure that I would also bond to ground.

Many industrial enclosures use a backplane (flat piece of painted steel) which is spaced out from the actual rear of the enclosure by standoffs. That way the backplane can be either assembled offline and then installed into the enclosure, or else drilled and tapped in-situ without piercing the rear of the enclosure.

I would think that you could probably place the contactor and transformer (+ fuseblock as suggested) in an 8x8 enclosure with pretty good room to work.

Is the fuse block for the 24v circuit? If so, i though that transformers had a built in fuse.

Thanks

 

[AndrewRT]

Shutting the main power on and off to the heater can't be the best way. There has to be a control circuit somewhere that you can tap into.

What does the heater have for controls? I don't follow what you say about it having a heat control but not an automatic shutoff.

The unit has built in manual on/off switch and a knob to adjust the wattage for higher or lower heat outputs. So what i mean by an automatic shutoff is the heater doesn't shut off at a set temperature, it will continually run until i shut it off manually.

 

[nsula_country]

I would not use a contactor on the line voltage wires. Most electric heaters continue to run the fan until the temperature in the housing or plenum is below a setpoint.

I would tap into the control wires that come from the heater switch. Set switch in the on position, use thermostat to control a 24v contactor, then wire switched leads through contactor. Fan will still operate through the safety temperature switch... At least without knowing how your heater is setup, seems logical.

CT

 

[AndrewRT]

I would not use a contactor on the line voltage wires. Most electric heaters continue to run the fan until the temperature in the housing or plenum is below a setpoint.

I would tap into the control wires that come from the heater switch. Set switch in the on position, use thermostat to control a 24v contactor, then wire switched leads through contactor. Fan will still operate through the safety temperature switch... At least without knowing how your heater is setup, seems logical.

CT

I just had a look at the circuit diagram in the instruction manual for the heater and from what i could see there is nothing in the circuit that would continually run the fan until the temperature dropped below a certain tempurature. Also if i were to tap into the control wires in the heater i could potentially void the manufacturer warranty.

Thanks, I appreciate your feedback.

 

[wyliesdiesels]

The one thing you havent told us is the brand and model of the heater??

Perhaps we can look up a manual and see if there is a way to tie into the control circuit.

I would not use a contactor on the line voltage wires. Most electric heaters continue to run the fan until the temperature in the housing or plenum is below a setpoint.

I would tap into the control wires that come from the heater switch. Set switch in the on position, use thermostat to control a 24v contactor, then wire switched leads through contactor. Fan will still operate through the safety temperature switch... At least without knowing how your heater is setup, seems logical.

CT

 

[AndrewRT]

The one thing you havent told us is the brand and model of the heater??

Perhaps we can look up a manual and see if there is a way to tie into the control circuit.

Yeah for sure, I forgot to include that in the original post.

Dr. Infrared DR966

 

[AntonLargiader]

http://ilivingusa.com/manuals/DR-966.pdf

The dial is apparently a thermostat. Not a numeric one, but it cycles the unit on and off to maintain a constant temperature.

If you want to control it with a standard stat, your setup looks right to me. Note that the manual specifies a 35A breaker.

 

[n20junkie]

I used a contactor to control the fan power on my modine heat exchanger that was tied to the houses boiler.

When the zone valve was activated for the garage, the fan contactor closed. Thenonly bad part was that at first the fan would blow cool air before the hot water made its way to the heat coils. But it worked great and is still going (I have since sold the hoise it was in).


I have an electric heater in my new garage. I took one leg for the power off and connected it to a 120v contactor. That contactor is connected to a z-wave plug in module. Now my garage heater can be turned on via iphone/ipad or via voice control. Same theory as what the OP wants to do.

 

[matt_i]

You could add the additional fan runtime feature but would require breaking one of the fan motor leads out of its oem connection and using a timer-off delay relay. Something for future

 

[mm08822]

After reading the manual it is obvious how they cut costs at the end users inconvenience.

Even their control scheme seems drop out the fan independent of residual heat remaining in the unit-unless they have an off delay built in to the t-stat.

Another option you may want to consider:
If you can live with setting one temperature (up high on the unit's controller), then you could make life easy on yourself and just install a local 2 pole disconnect switch at floor level for basic on/off control of the unit. If you went this route, I would go to a 60a disconnect as your unit is pushing the 80% limit for a 30A and you could cycle it on/off many times at the disconnect while unit is running. This should give you plenty of contact life in the disconnect.

 

[nsula_country]

I just had a look at the circuit diagram in the instruction manual for the heater and from what i could see there is nothing in the circuit that would continually run the fan until the temperature dropped below a certain tempurature. Also if i were to tap into the control wires in the heater i could potentially void the manufacturer warranty.

Thanks, I appreciate your feedback.

This is the last thing I would worry about when modifying a cheap, Chinese heater. Menards (I think) recently had these on sale for $69. Externally controlling the heater could violate warranty too...

Manual says it has mechanical thermostat. Set it once, then control with a 2 pole switch or disconnect. Done.

CT

 

[AndrewRT]

Im a little confused on how i should wire this now, should i wire it just like the diagram i drew just with an added fuse, or should i tap into the internal wiring on the heater?

 

[nsula_country]

You don't want to void the warranty... Don't open it.

If you are confused, you don't understand the schematic and the how components that you want to use need to be installed.

The schematic is simple if you don't value the import heater warranty... This is a simple, low voltage contactor project.

CT

 

[AndrewRT]

You don't want to void the warranty... Don't open it.

If you are confused, you don't understand the schematic and the how components that you want to use need to be installed.

The schematic is simple if you don't value the import heater warranty... This is a simple, low voltage contactor project.

CT

I don't really care if i void the warranty, but should I just wire it exactly how i have it setup in my schematic?

 

[nsula_country]

Yes, your schematic is correct...

I would recommend a 40 amp contactor. About $10 at a HVAC supply house. 6kw = 25 amps. Price between 30a and 40a are negligible. Also a 40va transformer is recommended, also about $10. These are common items. 30 amp 2 pole switch will be fine.

CT

 

[AndrewRT]

Yes, your schematic is correct...

I would recommend a 40 amp contactor. About $10 at a HVAC supply house. 6kw = 25 amps. Price between 30a and 40a are negligible. Also a 40va transformer is recommended, also about $10. These are common items. 30 amp 2 pole switch will be fine.

CT

Ok thanks for your help.

 

[tfi racing]

I have a couple of these laying around if anyone wants them,only rated for 25A though.

White Rogers 24A01G-3

http://www.emersonclimate.com/Documents/White-Rodgers/instruction_sheets/0037-4701.pdf

 

[AndrewRT]

Yes, your schematic is correct...

I would recommend a 40 amp contactor. About $10 at a HVAC supply house. 6kw = 25 amps. Price between 30a and 40a are negligible. Also a 40va transformer is recommended, also about $10. These are common items. 30 amp 2 pole switch will be fine.

CT

Ok perfect, should I also install a fuse on the 24v circuit? And is it ok to a 40a contactor on a 30a circuit?

 

[wyliesdiesels]

Ok perfect, should I also install a fuse on the 24v circuit? And is it ok to a 40a contactor on a 30a circuit?

A fuse woukdnt hurt but not necessary.

The 40a contactor is fine. Being overrated could potentially lengthen its lifecycle.

 

[nsula_country]

Ok perfect, should I also install a fuse on the 24v circuit? And is it ok to a 40a contactor on a 30a circuit?

Two crimp on spade connectors and a 3 amp automotive ATO blade fuse (pink)... Done! Perfectly fused and will blow before the xformer.

CT

 

[nsula_country]

A fuse woukdnt hurt but not necessary.

The 40a contactor is fine. Being overrated could potentially lengthen its lifecycle.

Correct. The contacts are larger, longer life. No need pushing the amp rating of import electrical parts.

CT

 

[sberry]

I have a couple of these laying around if anyone wants them,only rated for 25A though.

White Rogers 24A01G-3

http://www.emersonclimate.com/Documents/White-Rodgers/instruction_sheets/0037-4701.pdf

What would one want for one?

 

[Ainsley]

I did pretty well the same thing in my Shop as a temporary solution until I can afford a gas fired unit heater.

 

[nsula_country]

I did pretty well the same thing in my Shop as a temporary solution until I can afford a gas fired unit heater.

Controls Engineers strike again!

CT