Home work question?

[K2X]

The MDP is a 1200 amp. 3 phase, 4 wire service, and will have four parallel sets of conductors feeding it with four seperate conduits. What is the minimum size of the ungrounded conductor??

I'm not looking for the answer but I can't get past the 4 parallel sets feeding 3 phase. Shouldn't 3 parallel sets feed 3 phase?? Thanks for any help..

 

[chris kennedy]

Shouldn't 3 parallel sets feed 3 phase??

The number of parallel conductors is based on ampacity. The fact that this is 3? has nothing to do it.

 

[jumper]

See if this helps also:
http://www.mikeholt.com/instructor2/img/product/pdf/1220452298sample.pdf

 

[infinity]

They're asking about 4 sets of 4 conductors in each parallel set. What's the smallest conductors that you could use in each set. Basically you want to take the ampacity, 1200 amps and divide by the number of sets required then find you minimum conductor size.

 

[chris kennedy]

They're asking about 4 sets of 4 conductors in each parallel set. What's the smallest conductors that you could use in each set. Basically you want to take the ampacity, 1200 amps and divide by the number of sets required then find you minimum conductor size.

Never mind, its me that has a reading comprehension problem.

 

[infinity]

You missed the 'grounded conductor' part of the question.

You lost me, what does that have to do with the ampacity of the ungrounded conductors?

 

[K2X]

They're asking about 4 sets of 4 conductors in each parallel set. What's the smallest conductors that you could use in each set. Basically you want to take the ampacity, 1200 amps and divide by the number of sets required then find you minimum conductor size.

Ok ,so I could be putting a black, red, blue,white, in each of the four conduits? And maybe a green? So 510.16 and a little derating I should have my answer? Thanks !! ...Four conduits seemed a little strange but I guess it would work..

 

[jumper]

How about A phase, B phase, C phase (ungrounded conductors), Ungrounded conductor phased white, and using an approved conduit as the grounded conductor, and maybe no derating will be needed? Does this make sense?

 

[chris kennedy]

How about A phase, B phase, C phase (ungrounded conductors), Ungrounded conductor phased white, and using an approved conduit as the grounded conductor, and maybe no derating will be needed? Does this make sense?

That makes no sense at all??? I think you have chris kennedy disease! Can we just start this thread over?

 

[iMuse97]

Ok ,so I could be putting a black, red, blue,white, in each of the four conduits? And maybe a green? So 510.16 and a little derating I should have my answer? Thanks !! ...Four conduits seemed a little strange but I guess it would work..

That's the basic idea; but don't you mean T310.16?

 

[infinity]

Ok ,so I could be putting a black, red, blue,white, in each of the four conduits? And maybe a green? So 510.16 and a little derating I should have my answer? Thanks !! ...Four conduits seemed a little strange but I guess it would work..

Yes, that is correct. Now you need to figure out the minimum size of the ungrounded conductors by using Table 310.16.

 

[jumper]

Ok ,so I could be putting a black(A phase), red(B phase), blue(C phase),Ungrounded Conductors, white(grounded conductor), in each of the four conduits? And maybe a green?( maybe not needed if RMC, IMC, or EMT is used as EGC) So 510.16 and a little derating I should have my answer? Thanks !! ...Four conduits seemed a little strange but I guess it would work..

Most exam questions are for a minumum conductor size and conduit size so I was trying to eliminate a conductor, also trying to teach proper terminology. Is this better?

Also I see where I messed up earlier post, typed too fast and wrote wrong terminology, my apologies. Thank you Chris for pointing this out.

 

[tunny]

O,k, I'm missing somthing here, Mike holts book understanding the Nec requirements for grounding and bounding says...When circ cond are run in Paralell 310-4 ,an Equipment grounding cond must be installed with each set and sized in accordance with 250-122..But Nec clearly phrase's 310-4(E) " Where Paralell Equipment grounding conductors "Are used", They shall be sized in accordance with 250-122 ".To me this indicates the raceway could be used as the EGC. Can someone clear this up for me.,Thank's.

 

[infinity]

O,k, I'm missing somthing here, Mike holts book understanding the Nec requirements for grounding and bounding says...When circ cond are run in Paralell 310-4 ,an Equipment grounding cond must be installed with each set and sized in accordance with 250-122..But Nec clearly phrase's 310-4(E) " Where Paralell Equipment grounding conductors "Are used", They shall be sized in accordance with 250-122 ".To me this indicates the raceway could be used as the EGC. Can someone clear this up for me.,Thank's.

Yes, metallic raceways are permitted to serve as an EGC. If a wire type EGC is pulled in the conduits then there must be one in each of the parallel conduits sized according to the OCPD ahead of the feeder.