ampacity

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liquidtite

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when trying to find out the ampacity of an insulated conductor table 310.16 comes into play.then depending on the type of insulation you are using and what the degree rating of the equipment is you can pic what degree .what happens if your equiptment is rated for 60* but the type of insulation is in the 90*
 
ok so say if you were using nm witch is 60* and you were going to terminate the conductor on equiptment rated at 75
 
liquidtite said:
ok so say if you were using nm witch is 60* and you were going to terminate the conductor on equiptment rated at 75
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Say you have four 12-2 nm cables that are bundled and we must derate. The wire in NM is rated 90C so we look and see that #12 is rated 30 amps. We go to T. 310.15(B)(2)(a) and we see that for 8 current carrying conductors we need to derate 70%. 70% of 30 is 21 amps so a 20 amp breaker is fine. The 75C is this case means nothing since the wire in NM is rated 90C. The final ampacity cannot be greater than the weakest link in the circuit.
 
ok so say if you didnt have to drate dosnt the degree of what your terminating to determine what colum you would use
 
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liquidtite said:
when trying to find out the ampacity of an insulated conductor table 310.16 comes into play.then depending on the type of insulation you are using and what the degree rating of the equipment is you can pic what degree .what happens if your equiptment is rated for 60* but the type of insulation is in the 90*
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You must use the 60 degree column in this case.
 
As SQ stated, since were discussing NM cable the limiting factor is 60? C regard less of the terminal or insulation value due to 334.80.
 
liquidtite said:
ok so say if you didnt have to drate dosnt the degree of what your terminating to determine what colum you would use
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Again the limitation is the weakest link in the chain. If you have 90 degree terminations and 90 degree wire but are using NM then the nm is limited to 60C and thus it is the weakest link. If it were 75C wire with 90C terminations then you are limited to 75C. If the wire is 105C and the terminations 60C then you are limited to 60C- the weakest link.
 
liquidtite said:
thanks now I understand :happyno:
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Okay what are you asking. NM is limited to 60C based on 334.80 but the wire in NM is 90C rated-- confusing yes but as a cable it is 60C. You may use the 90C to derate but the final ampacity is limited to the 60C since that is what NM is rated.

Gives us a real example or two. I don't know how else to explain it.
 
I understood the example you gave me last post thanks for your time . I wasnt asking the question from an example I came across in the field I just wanted to gain the knowledge.what i was woundering was say if you were using thhn[90*)conductor and its connected to a 75* termination witch most ocps are, from what youve told me the ampacity would be limited to the 75* coloum and you wouldnt use the 90*coloum
 
liquidtite said:
I understood the example you gave me last post thanks for your time . I wasnt asking the question from an example I came across in the field I just wanted to gain the knowledge.what i was woundering was say if you were using thhn[90*)conductor and its connected to a 75* termination witch most ocps are, from what youve told me the ampacity would be limited to the 75* coloum and you wouldnt use the 90*coloum
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That is correct unless you need to de-rate. You did say earlier- no de-rating so I assume that is what you were asking. :thumbsup:

The good thing about 90C wire is it helps use when we have to de-rate otherwise it isn't much help except in a few cases.
 
liquidtite said:
when your drateing it dosnt matter what * the conductor is you always use the 90* coloum right
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If the conductors have 90? insulation. Most of your new work that will be the case. If you are dealing with some older work you need to pay attention you may only have 60? or 75? insulation on the existing conductors.
 
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