Multiple Heaters on 30 amp circuit question

[mousebob]

Hello,

I have a question regarding wiring multiple heaters. I currently have an existing 240v 30 amp circuit with 10 gauge wiring.

I would like to place 2 individual heaters and 2 thermostats on this circuit. Each heater is 240v 2250 watts and would be served each by a thermostat. The thermostats are only rated to 15 amps each.

Is this acceptable since each heater will only draw ~10 amps? Do I need to use 10 gauge wire for all the wiring between the thermostat and heater or is 12 gauge acceptable?

Thanks!

 

[sberry]

What size wire does the heater have? Is there an instruction manual?

 

[ycgoat]

For amperage you need to go by the Full Load Amps (FLA) listed on the heater not the element wattage. Technically yes the #12 wire can support, is legal is up to the Authority having justification.


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[u2slow]

For amperage you need to go by the Full Load Amps (FLA) listed on the heater not the element wattage. Technically yes the #12 wire can support, is legal is up to the Authority having justification.

Many heaters are only listed with wattage@voltage. #14 would even be fine for 9.375A as far as loading. But of course, there may be higher minimums for legality, as per the AHJ.

 

[mousebob]

My question ultimately is about the cable and thermostat.

I know that on 20 amp circuits we always use 15 amp receptacles because they can handle this load as a pass through.

Is the same true with the scenario I described above using a 15 amp thermostat on a 30 amp circuit? I understand the heater load itself will be only around 10 amps but does the 15 amp thermostat ultimately pose a fire risk if more amperage were to pass through it? Especially since the breaker would not trip until 30 amps.

I also learned to NEVER use "under-rated" wire on a circuit. For example, we never use 14 gauge wire on a 20 amp circuit. However, on the design above I would be running 12 gauge wire from a thermostat to the heater.

Thanks for all the help thus far.

 

[ycgoat]

Mike Holt is a good on line recourses, I would say Tap rule 10’=10%


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[alfredeneuman]

Could you provide a link to the heaters?
Are they line voltage thermostats?
The maximum circuit size for fixed heaters is 30 Amps.
You have to consider heaters a continuous load and multiply by 125%.
2250/240 = 9.375
9.375X1.25 = ~11.72 amps each.

 

[ycgoat]

The tap rule applies to the wire.


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[alfredeneuman]

Mike Holt is a good on line recourses, I would say Tap rule 10’=10% Sent from my iPhone using Tapatalk

The feeder tap rules are just for moving overcurrent devices from the source closer to the load, and have to terminate in either a circuit breaker or fuses.
Nowhere does it mention 10'=10%.
They don't qualify as a fixture tap.

 

[ycgoat]

AHJ


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[mousebob]

Yes, they are line current thermostats. Here is a link to the heaters: https://king-electric.com/product/model-paw/.

I am looking at the 2250w 240v model.

The thermostat is the second one on this page: https://king-electric.com/products/thermostats/line-voltage-thermostats/

Thanks!

 

[alfredeneuman]

AHJ

Why does it qualify as a tap conductor?

 

[Kensico]

If you are using a 30 amp breaker, you can’t put any wire smaller than #10 awg. The circuit breaker is there to protect the wire.

 

[mousebob]

If you are using a 30 amp breaker, you can’t put any wire smaller than #10 awg. The circuit breaker is there to protect the wire.

Does the same apply to the thermostat (rated at 15 amps) then? Also, I am certain the wiring in the heater is not 10 gauge.

 

[wyliesdiesels]

Does the same apply to the thermostat (rated at 15 amps) then? Also, I am certain the wiring in the heater is not 10 gauge.

The heaters will not pull more than their rating so the thermostats are fine.

The wiring in the heater is listed for the appliance and is not the same type of wire used inside the walls. often heating appliances have 105° C rated wire. Building wire final ampacity is limited to 75° c ampacity.

The manufacturer's directions give info on how to size the wire.

While not specifically stating the 1.25 multiplier in the first link, they show this by showing max 12a for #14. The second link does list the 20% deration

https://king-electric.com/wp-content/uploads/kel_product_files/PAW-Installation-Instructions.pdf

The link below describers how to size a circuit for multiple heaters

2250 * 2= 4,500
4,500 / 240 = 18.75a
18.75 * 1.25 = 23.44a

#10 wire and 30a breaker required.

https://king-electric.com/pro-tips/sizing-the-heater-circuit/

 

[ycgoat]

The thermostats would be subject to the full fault current of the 30 amp circuit


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[wyliesdiesels]

The thermostats would be subject to the full fault current of the 30 amp circuit


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Fault current is hundreds higher than the breaker rating

The wire would be subject to it as well...

or did you mean overcurrent? 2 different things....

 

[Kensico]

Does the same apply to the thermostat (rated at 15 amps) then? Also, I am certain the wiring in the heater is not 10 gauge.

The circuit breaker protects the wire it is connected to, not the appliance

 

[ycgoat]

The wire can be as small as #14, if less than 25’. 15 amp thermostats should be fine too.


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[ycgoat]

The wire can be as small as #14, if less than 25’. 15 amp thermostats should be fine too.


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The ground wire has to be sized based on the 30 amps but never has to be larger than the branch wire


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[alfredeneuman]

The tap rule applies to the wire.

Please provide a Code citation to substantiate this.

 

[sberry]

Lots of wire smaller than 10 connected to 30A.

 

[ycgoat]

Please provide a Code citation to substantiate this.

A quick web search says article 240.21 for feeder taps, but there are other code sections that apply to residential loads and fixed space heaters.


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[ycgoat]

The code section above does not specifically say it applies to residential heaters, the other sections do not specifically ref the tap rule as an exception SO it is subject to the interpretation of the AHJ.

I have done this with residential lighting circuits, where the AHJ approved it.


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[alfredeneuman]

So you have no Code ref to substantiate, other than you've done it before on light circuits, and some AHJ in Va. passed it?

 

[ycgoat]

What are you talking about? I posted the code section that allows for feeder taps. Where is the code section that says he can not. I gave a legit justification based on the code for doing as he suggested. There are legit arguments based on the code of why he should not.

You offered no legit information based on any thing other than generalities.


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[alfredeneuman]

I posted the code section that allows for feeder taps.
You offered no legit information based on any thing other than generalities.

Obviously you know that 240.21 does not apply, and the wording for the Article is too long to post here.
"but there are other code sections that apply to residential loads and fixed space heaters." Name one that will shed some light on your claim.

 

[ycgoat]

Name 1 that says otherwise and explain why it negates the tap rule.


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[ycgoat]

There is an answer that negates the tap rule and another exception that gives a way around that.


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