Does this question really have an answer?

[George Stolz]

I was looking over a friend's RW exam, and came across this question:

The maximum allowable overcurrent protection for four 14/2 NM cables installed in contact with thermal insulation without maintaining spacing between cables is:

I'm not going to bother throwing the answers on there. I'd say this is an unanswerable question. Any takers as to why I think that?

 

[nunu161]

the current the conductors can carry is reduced not the overcurrent protection device

 

[quogueelectric]

They didnt give you ambiant temperatures??

 

[nunu161]

idk if ambient temperatures need to apply for bundling conductors and derating

 

[infinity]

Seems like they're asking about this:

334.80 Ampacity.
The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15. The ampacity shall be in accordance with the 60?C (140?F) conductor temperature rating. The 90?C (194?F) rating shall be permitted to be used for ampacity derating purposes, provided the final derated ampacity does not exceed that for a 60?C (140?F) rated conductor. The ampacity of Types NM, NMC, and NMS cable installed in cable tray shall be determined in accordance with 392.11.
Where more than two NM cables containing two or more current-carrying conductors are installed, without maintaining spacing between the cables, through the same opening in wood framing that is to be fire- or draft-stopped using thermal insulation, caulk, or sealing foam, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(2)(a) and the provisions of 310.15(A)(2), Exception, shall not apply.
Where more than two NM cables containing two or more current-carrying conductors are installed in contact with thermal insulation without maintaining spacing between cables, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(2)(a).

 

[George Stolz]

Suppose those four cables are supplying an air conditioner.

 

[winnie]

Or suppose that those 4 cables were all supplied by the _same_ breaker

-Jon

 

[wbalsam1]

I read the question as having it's intent founded in 334.80. :smile:

 

[Cold Fusion]

George -
I'm definitely out of my element - I don't do romex (which means I may not have a clue)

Wouldn't 240.4.B also apply and allow a 15A CB? Of course, the calculated load would have to be no more than the reduced ampacity.

cf

 

[Inspectorcliff]

rw renewal #8

rw renewal #8

I was looking over a friend's RW exam, and came across this question:



I'm not going to bother throwing the answers on there. I'd say this is an unanswerable question. Any takers as to why I think that?

Master George, as a party to whom wrote the refresher exam. Try the following and see if doesn't get you close or exact.

? 334.80, 310.16, 310.15B2a, 240.4D :grin:

 

[tkb]

Since the smallest standard breaker per 240.6(A) is 15 amps, isn't the answer 15 amps?

 

[Inspectorcliff]

yep

yep

Since the smallest standard breaker per 240.6(A) is 15 amps, isn't the answer 15 amps?

That would be exact. as per the 2008 National Electric Code.

 

[RonPecinaJr]

I was looking over a friend's RW exam, and came across this question:



I'm not going to bother throwing the answers on there. I'd say this is an unanswerable question. Any takers as to why I think that?

The answers got to be 15. We were discussing this same thing on another board and no derating needs to be done until there are more than two cables. Trick question, and a good one at that.

 

[George Stolz]

That would be exact. as per the 2008 National Electric Code.

The maximum breaker I can put on one of those cables is not 15A.

The ampacity of the cables is 17.5 amps, but under some conditions I can throw them on almost anything. 240.4(E), (G).

 

[RonPecinaJr]

The maximum breaker I can put on one of those cables is not 15A.

The ampacity of the cables is 17.5 amps, but under some conditions I can throw them on almost anything. 240.4(E), (G).

Like an A/C condensing unit, or a motor.

 

[C3PO]

I don't think it is a trick question.
Four 14/2 cables = 8 ccc

25A x .70 = 17.5 A , but we are still limited to 15A by 240.4(D)(3)

I see where you are going with this George but this would be my answer if I was taking the test.

This confusion could have been cleared up with a brief description of what these cables run, in the question.

 

[Inspectorcliff]

Hello

Hello

The maximum breaker I can put on one of those cables is not 15A.

The ampacity of the cables is 17.5 amps, but under some conditions I can throw them on almost anything. 240.4(E), (G).

The question doesn't say under Tap Conductors, and it doesn't say under Specific Conductor Applications. But it does read: 8.) The maximum allowable overcurrent protection for four 14/2 NM cables installed in contact with thermal insulation without maintaining spacing between cables is: And then it gives you and ampacity option. Master George.

 

[wirebender]

Then it should read "maximum allowable ampacity".
IMHSO

 

[Inspectorcliff]

hummmmmmmm

hummmmmmmm

Then it should read "maximum allowable ampacity".
IMHSO

It surely could have, it didn't, but it might in say Texas. If it was applicable. thanks.

 

[George Stolz]

The question doesn't say under Tap Conductors, and it doesn't say under Specific Conductor Applications. But it does read: 8.) The maximum allowable overcurrent protection for four 14/2 NM cables installed in contact with thermal insulation without maintaining spacing between cables is: And then it gives you and ampacity option. Master George.

The thing is, I must read all test questions as, "What do they want to verify I know or can find?" There are so many possible things this question could be attempting to verify that I know, that for the test-taker, it becomes a gut check and a best guess.

I think if the question mentioned a breach of 240.4(B)(1), then it would have been a solid question, JMO.