Branch Circuit Capacity Check

[Jawgarage]

Looking to see IF I can put two electric baseboard heaters on a single 240v branch circuit with a 20amp double pole breaker using 12/2 w/ground wire. Heaters are 2000W each. And yes, now that the temps have hit the upper 90’s I am running wire in the attic and garage to install heater circuits!!!!!! Nuts.....

Jeff

 

[awdblazer]

negative

 

[budmur]

More knowledgeable people than me might chime in, but from my calculator:

2x2000w = 4000w

4000w / 240v = 16.7Amps

Looks OK to me.

 

[awdblazer]

2x2000w=4000w
4000/240=16.7amps
since its a heating load
16.7/0.8=20.83amps so 10/3 is needed

 

[Jawgarage]

Thanks guys. I thiught not as the max for a 20amp 240v circuit using 12/2 is 16 amps and this would work out to 16.7 amps. I know its close, but have you seen the xost if a roll of 10/2 lately?? 10/3?? WOW! But I also dont want to draw too much current over the 12/2 and keep blowing the circuit or worse yet start a fire in my “little project”.

Jeff

 

[Norcal]

2x2000w=4000w
4000/240=16.7amps
since its a heating load
16.7/0.8=20.83amps so 10/3 is needed

Why suggest 10/3 when a neutral is not required? Wasting money.

 

[wyliesdiesels]

Awdblazers math is correct.

However, OP mentioned running the wire in the attic and so temperature correction factors are needed as well but since #10 is required, the correction factor calc probably wont go over #10.

 

[Bert_]

Are we really talking about derating for ambient temp? I mean the heaters are going to be used when it is COLD.

I'd run them on #12 in a second. We are only using 80% of the circuit capacity so I think there is a enough wiggle room for that extra 6/10'ths of an amp.

 

[wyliesdiesels]

Are we really talking about debating for ambient temp? I mean the heaters are going to be used when it is COLD.

I'd run them on #12 in a second. We are only using 80% of the circuit capacity so I think there is a enough wiggle room for that extra 6/10'ths of an amp.

Oh duh.

Even though the thread is about heaters, I had AC and hot attic temperatures on the brain living in the central valley desert..

 

[Jawgarage]

So if I read these correctly “the book” says two 2000W 240v baseboard heaters if on a single branch circuit need to use a 30amp dual pole breaker with 10/2 wire. BUT due to the only very slight amp overage some folks say it’s OK to use 12/2 with a 20amp dual pole breaker. Isnt the code book there for a reason?

 

[PCustoms]

Isnt the code book there for a reason?

One would think it's to clarify ambiguities, but hey, maybe it works on 12, maybe it doesn't.

I know its close, but have you seen the xost if a roll of 10/2 lately?? 10/3?? WOW! But I also dont want to draw too much current over the 12/2 and keep blowing the circuit or worse yet start a fire in my “little project”.

Jeff

If you've got money to build that you've got money for a roll of 10/2.

 

[Bert_]

So if I read these correctly “the book” says two 2000W 240v baseboard heaters if on a single branch circuit need to use a 30amp dual pole breaker with 10/2 wire. BUT due to the only very slight amp overage some folks say it’s OK to use 12/2 with a 20amp dual pole breaker. Isnt the code book there for a reason?

Code say's electric heater circuits should be sized 125% because it is considered a continuous load. That is an extra margin for safety and to prevent nuisance trips. At 16.7 amps we are just over the allowed current for a 20 amp circuit. 125% got picked because it was a nice round number, do not think that having a circuit that is only 120% will suddenly cause problems. You will still have a 20% margin for safety.

Personally I would use some common sense and decide that an extra 0.7 amp will never cause an issue, even if both heaters were running 24/7 which is extremely unlikely.

It is not exactly to the letter of the code but I wouldn't worry about it a little common sense goes a long way.

 

[Dagny]

You don't think it will burst into flames?

 

[awdblazer]

fyi 10/3 is cheaper to buy than 10/2 as 10/3 is more commonly used

 

[AntonLargiader]

fyi 10/3 is cheaper to buy than 10/2 as 10/3 is more commonly used

Here in Charlottesville at Lowes:
10/3 = $197 for a 250' roll
10/2 = $137 for a 250' roll

 

[Jarvis]

How many feet are you running the wire?
Why not just temp hook one up at the panel and check amp draw. Sometimes it pulls less amps than noted.

 

[wyliesdiesels]

How many feet are you running the wire?
Why not just temp hook one up at the panel and check amp draw. Sometimes it pulls less amps than noted.

Have to go by nameplate wattage

 

[05wrangler]

I would just go with 10/2 and be done with it. at the end of the day, its your call. the code is 125% your calculations are at 20.89. you now have the knowledge you need. you can pick rather you want to violate the code and maybe be just fine or do it right.