110.14(c)

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joebell

joebell

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New Hampshire
Is this installation correct?

I need to provide a 60 amp circuit to a piece of lab equipment. According to 110.14(C)(1)(a) I need to size to these conductor so as not exceed the ampere rating of the 60 degree C column. I am installing conductors with type THHN insulation.

My question is if both the disconnect and the CB have a dual rating of 60/75 degree C is it permissable to use the 75 degree C column for the conductors ampere rating? That is how I am interpreting 110.14(C)(1)(a)(3) is this right?


Joe
 
you are correct, taking into account any other limiting factor (ambient, type NM cable limitations, etc.)
 
THHN is a 90 degree conductor so for your application it can be used at it's 75 degree ampacity which is 65 amps. You also are permitted to use a 70 amp OCPD since 65 amps is not a standard size and may be increased to the next standard size if your connected load is 65 amps or less.
 
joebell said:
Is this installation correct?

I need to provide a 60 amp circuit to a piece of lab equipment. According to 110.14(C)(1)(a) I need to size to these conductor so as not exceed the ampere rating of the 60 degree C column. I am installing conductors with type THHN insulation.

My question is if both the disconnect and the CB have a dual rating of 60/75 degree C is it permissable to use the 75 degree C column for the conductors ampere rating? That is how I am interpreting 110.14(C)(1)(a)(3) is this right?


Joe
Click to expand...

110.14(C)(1), "..... Unless the equipment is listed and marked otherwise, ....."
You gotta build it according to the weakest link
1] lug
2] wire
3] raceway

110.14(C)(1)(a) is telling you that certain lug sizes should be assumed to be 60?C unless marked otherwise. . If marked otherwise, you can use it as marked. . 75?C is very very common marking for smaller lug sizes.

Your THHN wire is rated 90?C per T310.16

Sometimes you get a raceway restriction [Romex; 334.80 60?C or PVC; 352.12(E) usually limited to 75?C, encased outdoors 90?C]

You usually find out that your weakest link is 75?C.
 
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