ampacity of wire

[Jessehop]

In preparing of the exam I had a question that read...What is the ampacity of six current carring 4/0 xhhw conductors in a slab (wet location)?
none of the answers I came up with were in the multiple choice. How do you figure this?

 

[Dennis Alwon]

In preparing of the exam I had a question that read...What is the ampacity of six current carring 4/0 xhhw conductors in a slab (wet location)?
none of the answers I came up with were in the multiple choice. How do you figure this?

I hope those conductors are in a pipe in the slab. How about sharing with us what you did. Also is there anymore info than that?

 

[infinity]

What did you come up with? 416 amps?

 

[Dennis Alwon]

What did you come up with? 416 amps?

Look at Table 310.13 for Xhhw. There is a clue there.

Then go to table 310. 16

Next look at Table 310.15(B)(2)(a)-- another clue.

Also is the conductor copper or aluminum???

416 is not even close

 

[Pierre C Belarge]

Dennis
It could be 416 amp if this is single phase, I believe you may be thinking 3 phase.

 

[infinity]

I assumed XHHW-2. I should have read the OP more closely.

4/0 CU XHHW (75 degrees in wet location) = 230 amps * 2 sets * 80% = 368 amps.

4/0 CU XHHW-2 (90 degrees in wet location) = 260 amps * 2 sets * 80% = 416 amps

 

[Dennis Alwon]

I assumed XHHW-2. I should have read the OP more closely.

4/0 CU XHHW (75 degrees in wet location) = 230 amps * 2 sets * 80% = 368 amps.

4/0 CU XHHW-2 (90 degrees in wet location) = 260 amps * 2 sets * 80% = 416 amps

Well I was taking the question at face value. I was stating that the wires with derating would be rated 230 *80% . No one said they were parallel conductors. I assumed the question just wanted the ampacity of the 4/0 copper. I was not thinking that it was parallel conductors and the question does not say they are so....... to me 4/0 with 80% derating. I would not have thought to multiply it by 2 with the wording of the question.

 

[Dennis Alwon]

Dennis
It could be 416 amp if this is single phase, I believe you may be thinking 3 phase.

Even if it were parallel single phase you would have to use 75C not 90 because XHHW in wet location is rated 75C. 368 amps

 

[infinity]

Dennis I agree more with your answer. For some reason I got stuck on the concept of a parallel feeder in the same conduit. Clearly the question didn't say that.:roll:

 

[Dennis Alwon]

Dennis I agree more with your answer. For some reason I got stuck on the concept of a parallel feeder in the same conduit. Clearly the question didn't say that.:roll:

Yeah, but who knows if the op gave us the entire question or if the question was one of those bad ones. I can see a possibility of 3 ways to interpret the question-- my , way, your way and Pierres suggestion of 3 phase. Who really knows what they were looking for. At least the OP can try all the methods.

 

[danickstr]

I would have assumed that it meant 6 conductors on one phase and derated based on 6 conductors in a conduit.

edit answer 1248 amps

 

[Dennis Alwon]

I would have assumed that it meant 6 conductors on one phase and derated based on 6 conductors in a conduit.

edit answer 1248 amps

We can assume all possibilities which only gives credence to a very poor question. Since Jesse has not responded with the choice of answers or anything else I guess we won't ever know.

 

[tonyou812]

I agree with Trevor, on the 75 degree column, and i do believe that if they were looking for parallel conductors they would have stated it. Try not to think to much. they usually give little hints to what they are looking for exactly

 

[jetlag]

Remember a test question like this

Remember a test question like this

I remember a question like this and they only wanted to see if you knew how to derate the six conductors at their max capacity each without regard to phase or parrallel. the correct answer for this case would have been 230x.8x6= 1104 amps . Of course one could say thats the same as 2 sets 3 ph at 552 amps each or 3 set single phase at 368amp each but thats not the answer they wanted

 

[jetlag]

correction

correction

I looked back in note book for license prep course and they only wanted an answer of 230 x .8 = 184amps each . doesnt matter if its 3 single phase 184 amp or 2 3 ph 184 amps or 6 parrallel 184 each

 

[Inspectorcliff]

We can assume all possibilities which only gives credence to a very poor question. Since Jesse has not responded with the choice of answers or anything else I guess we won't ever know.

I couldn't help but interject the possibility which :roll: there were no poor questions just some that make us think more than others.:wink:

 

[480sparky]

I couldn't help but interject the possibility which there were no poor questions just some that make us think more than others.

OK, so not as much as a 'poor question' as a 'poorly written' one, meaning it may lack all the necessary information to garner an answer.

 

[Charles R. Miller]

The maximum ampacity for a 4/0 XHHW conductor located in a wet location with a total of six current carrying conductors is 184 amperes. I have seen these types of questions many times on electrical exams.

The test writers are trying to trick people into selecting the 90 degree C column instead of the 75 degree C column. I?m sure one of the incorrect answers on the test is 208 amperes.

Charles