breaker size

[bark]

I have some #4 copper thwn which is rated at 85 amps. I know we used to be able to put a 90 amp breaker in front of it but was there a change a few years back that changed that or can we still do it?

Thanks in advance

 

[fmtjfw]

you can round up -- up to 800A CB

 

[Dennis Alwon]

#4 copper is good for 85 amps at 75C so if the calculated load is 85 amps or less than you can use a 90 amp overcurrent protective device based on 240.4(B)

 

[jumper]

If the calculated load is 85A or less you may utilize the rule in 240.4 to use the next standard size breaker of 90A.

 

[Dennis Alwon]

If the calculated load is 85A or less you may utilize the rule in 240.4 to use the next standard size breaker of 90A.

You're such a copy cat....

 

[jumper]

You're such a copy cat....

I saw that. Word for word in one part.

 

[dkidd]

you can round up -- up to 800A CB

hmy:

 

[jumper]

hmy:

He meant that the rule in 240.4(B) can be used up to a 800A breaker, not that OP could use a 800A breaker.

At first glance I thought the same thing.

 

[Dennis Alwon]

hmy:

Haha-- it is funny as it is written. Could be taken the wrong way

 

[Larry Bohn]

#4 copper is good for 85 amps at 75C so if the calculated load is 85 amps or less than you can use a 90 amp overcurrent protective device based on 240.4(B)

I agree. Wouldn't you also have to apply 110.14(C)1, and be sure the overcurrent device has 75C rated terminals?

 

[kwired]

I agree. Wouldn't you also have to apply 110.14(C)1, and be sure the overcurrent device has 75C rated terminals?

yes. Unless it is an old breaker that shouldn't be a problem though.

 

[Smart $]

#4 copper is good for 85 amps at 75C so if the calculated load is 85 amps or less than you can use a 90 amp overcurrent protective device based on 240.4(B)

...and 240.6(A), which lists standard OCP ratings.

Being the next lower standard rating is 80, the #4 can even be derated to 81A and the 90A breaker can still be used, once again as long as the load is not more than 81A.

 

[timtom58]

yes. Unless it is an old breaker that shouldn't be a problem though.

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