What is the de-rating percentage for 8 current carrying in a cord or conductors

[O'donisR]

• Hi everyone, I have problem solving this question that I failed on my exam: What is the de-rating percentage for 8 current carrying in a cord or conductors. The only info I see on the NEC is that where the number of current carrying conductors exceeds three, the allowable ampacity shall be reduce from 3 conductors rating as show in table 400.5.

I think the de-rating % should be calculated at 100%..


Thank you in advance!!

 

[kwired]

• Hi everyone, I have problem solving this question that I failed on my exam: What is the de-rating percentage for 8 current carrying in a cord or conductors. The only info I see on the NEC is that where the number of current carrying conductors exceeds three, the allowable ampacity shall be reduce from 3 conductors rating as show in table 400.5.

I think the de-rating % should be calculated at 100%..


Thank you in advance!!

Why you say 100%? That would mean no matter the size the ampacity is zero

 

[O'donisR]

Why you say 100%? That would mean no matter the size the ampacity is zero

for my interpretation of the code:where the number of current carrying conductors exceeds Eight, the allowable ampacity shall be reduce from 3 conductors rating as show in table 400.5. 3 carrying conductors shall be calculated at 100% means that no de-rating is needed.

 

[qcroanoke]

for my interpretation of the code:where the number of current carrying conductors exceeds Eight, the allowable ampacity shall be reduce from 3 conductors rating as show in table 400.5. 3 carrying conductors shall be calculated at 100% means that no de-rating is needed.

Are you saying that the first three conductors are figured at 100% ampacity and then start counting 1.2.3.4.5?
Meaning you have 8 conductors but derate applies to only 5?

 

[O'donisR]

Are you saying that the first three conductors are figured at 100% ampacity and then start counting 1.2.3.4.5?
Meaning you have 8 conductors but derate applies to only 5?

Thank you for reply, I don't I trying to understand this question......Question only ask for the de-rating percentage value for 8 current carrying conductors in a cord or cable. very confuse for me..

 

[qcroanoke]

Thank you for reply, I don't I trying to understand this question......Question only ask for the de-rating percentage value for 8 current carrying conductors in a cord or cable. very confuse for me..

derate percentage For 8 current carrying conductors in a cord or cable is 70%.

 

[qcroanoke]

Why you say 100%? That would mean no matter the size the ampacity is zero

or 100%

 

[O'donisR]

Are you saying that the first three conductors are figured at 100% ampacity and then start counting 1.2.3.4.5?
Meaning you have 8 conductors but derate applies to only 5?

I don't really remember the question very well, should be a missed a data, I will try to get the question right.. so far I know the answer is related with article 400.5.(Where the number of current carrying conductors exceeds three, the allowable ampacity or the ampacity of each conductor shall be reduced from 3-conductors rating as show in table 400.5)

So if I have 8 current carrying conductors in a cord or cable? how can I deduct the allowance ampacity? table 400.5..

 

[qcroanoke]

I don't really remember the question very well, should be a missed a data, I will try to get the question right.. so far I know the answer is related with article 400.5.(Where the number of current carrying conductors exceeds three, the allowable ampacity or the ampacity of each conductor shall be reduced from 3-conductors rating as show in table 400.5)

So if I have 8 current carrying conductors in a cord or cable? how can I deduct the allowance ampacity? table 400.5..

you would find the ampacity of the conductors in the cable according to the type of cable it is.
for example: SJO cord with #12 conductors from column A in table 400.5 A is good for 20 amps. you use column A because the last line of 400.5 A tells you too.
You have 8 current carrying conductors in your cable. therefore according to table 400.5 you have to derate those conductors to 70% of 20 amps. .70 x 20=14 amps.
I've probably made your confusion worse. My apologizes if I have.

 

[kwired]

Thank you for reply, I don't I trying to understand this question......Question only ask for the de-rating percentage value for 8 current carrying conductors in a cord or cable. very confuse for me..

Forgive my first reply, I don't think I understood just what you were asking at that time.

The use of 400.5(A)(3) is no different than using 310.15(B)(3)(a) except it applies to flexible cords instead of cables and raceways.

Your question mentioned 8 current carrying conductors, doesn't really matter at this point what those conductors are supplying or how many other "non current carrying conductors" may also be in the same cord.

The title of the table even kind of explains a little - "for more than three current carrying conducotors".

For three or less "current carrying" conductors, no additional adjustment is necessary. For three or more, use the adjustment factors in the table. The reason for adjustment is the heat produced within the conductors - the more current carrying conductors there are the more heat there will be, but larger conductors will have less resistance and will give up less heat. It is all about protecting the conductor insulation from overheating. You do not ignore the first three when counting the total number of current carrying conductors.