# Ampacity, Heater

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#### Joey94

##### Member
I have a heater that is 6000 watts 240V. So it uses 25Amps. In my 3/4 raceway there are 9 conductors from which 8 is current carrying. I’m wondering if my AWG 10 THHN with a 30 Amp breaker is the right size wire and amperage of breaker for it. Please advise

#### AC\DC

##### Senior Member
Need to put 125% on that heater load so you #10 won’t work
31.25 amps

#### Little Bill

##### Moderator
Staff member
You also have to derate 70% for 8 CCC.

#### infinity

##### Moderator
Staff member
You also have to derate 70% for 8 CCC.
Yup, and as AC/DC has pointed out even without the derating the #10's are too small.

#### Joey94

##### Member
So what would would be the correct wire size and breaker amperage?

This is the heater. Model number: LEH61
The specs say it’s 6000W 25Amp 240V
The wiring diagram says 20Amps per element. Which is kind of confusing.

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#### infinity

##### Moderator
Staff member
It says MAX 20 amps per element not 20 amps per element. The specifications say 6000 watts 25 amp @240 volt which is correct.

#### Dennis Alwon

##### Moderator
Staff member
It says MAX 20 amps per element not 20 amps per element. The specifications say 6000 watts 25 amp @240 volt which is correct.
Yes but 6000 watts/240 = 25 amps.... Don't we need to multiply by 125%== 31.25 amps

#### Joey94

##### Member
I’m guessing that’s if you want to have two separate circuits of 240V with two double pole breakers!?

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#### Dennis Alwon

##### Moderator
Staff member
I’m guessing that’s if you want to have two separate circuits of 240V with two double pole breakers!?

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I agree.. they probably have different models with higher wattage elements or in this case you can run 2- 20 amp circuits and be compliant

#### Joey94

##### Member
So in case of the 3 wire system application there is a need for 40 amp breaker ?

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#### infinity

##### Moderator
Staff member
Yes but 6000 watts/240 = 25 amps.... Don't we need to multiply by 125%== 31.25 amps
Yes, see post #2.

#### Joey94

##### Member
So what do you all think is the correct size wire and breaker ? With multiplying by 125% and derating 70% for 8 ccc

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#### augie47

##### Moderator
Staff member
Where are you getting the 8 cc conductor ?

#### wwhitney

##### Senior Member
So what do you all think is the correct size wire and breaker ? With multiplying by 125% and derating 70% for 8 ccc
First, the branch circuit conductors needs to have a table ampacity of 25A * 125% (continuous factor) = 31.25A at 75C, assuming 75C terminations at both ends. So that would be #10 Cu with an ampacity of 35A.

Second, the circuit conductors have to have a table ampacity of 25A / 0.7 (derating factor) = 35.7A at 90C, assuming 90C insulation. So again #10 Cu.

Lastly, the breaker has to be at least 25A * 125% = 31.25A, so a 35A breaker minimum But the small conductor rule limits #10 Cu to 30A breakers, with no exception for this application, so you'll need to use #8 Cu.

If you use #8 Cu with 90 C insulation, that has a table ampacity of 55A. So the derated ampacity is 38.5A. That means you can use a 40A breaker on it, if desired.

But if you used #8 Cu with 75C insulation, that has a table ampacity of 50A, giving a derated ampacity of 35A. For that you'd need to use a 35A breaker.

Cheers, Wayne

#### Joey94

##### Member
Thank you so much! This is exactly the answer I was looking for! Now it all makes sense

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#### Dennis Alwon

##### Moderator
Staff member
Thank you so much! This is exactly the answer I was looking for! Now it all makes sense

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Or if it is easier run 2-20 amp circuits

#### robertd

##### Senior Member
I’m guessing that’s if you want to have two separate circuits of 240V with two double pole breakers!?

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If you have two circuits on one switch would need a tie handle on all four breakers, or a 4-pole breaker. That doesn't seem very useful.

#### Dennis Alwon

##### Moderator
Staff member
If you have two circuits on one switch would need a tie handle on all four breakers, or a 4-pole breaker. That doesn't seem very useful.

I believe they make 4 pole breaker ties.

#### Joey94

##### Member
The switch for the heaters is a duplex. You can turn each element on or off separately. So that’s why the 5 wire application. In case you want them to be on separate circuit with separate double pole brakers. At least that’s how I understand the diagram.

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