Use of Parallel MC Feeders to Large Panels

[charlie b]

I have been asked to investigate the viability and possible cost savings of recommendations arising from a ?Value Engineering? review. The project includes several large buildings. One recommendation is to replace the current design of ?conduit and wire? with a design that uses MC cable, for feeders up to 1200 amps.

Example: Our current design has four parallel sets of 350 MCM cable, each including a 3/0 EGC, for the feeder to a 1200 panel. OK, so I can replace that with four parallel 350 MCM MC cables. But each cable would have to have a ?full size? ground, per 250.122F. My problem is figuring out how to get an MC cable with 350 MCM conductors and a 3/0 ground wire. Does anyone make such an animal? One manufacturer?s catalog that I have on my desk says that the EGC in a 350 MCM MC cable is size 3.

As I see it now, I can?t feed a panel rated higher than 225 amps with a single MC cable. Beyond that, I need parallel MC cables, and I can?t get an EGC large enough in an MC to allow parallel cables.

Any ideas or experiences to offer?

 

[charlie b]

To the above question, let me add that the catalog I have handy offers to include two EGCs in each MC cable, on request. However, for the 350 MCM cable, that would be a pair of #3 wires. I need a 3/0, and it would take three #3 wires to equal the cross-sectional area of a single 3/0. Also, I don?t think I can run three #3 wires, and take credit for that as being equivalent to a single 3/0. So that option seems to offer no solution to my problem.

 

[necnotevenclose]

Converting from P&W to MC is not all that easy. Just because the phase conductors may be large enough the EGC may not be. Last summer I ran into this problem when a contractor wanted to use MC. In many cases the size of the phase conductors would have to be increased in order to get the required size EGC, but with saying that some of the quantity of runs were reduced. But beware from 2500A and up the EGC is not oversized. The EGC for 2500A and above is sized in accordance with 250.122(A) which states the EGC shall not be required to be sized larger than the phase conductors. Also to make the oversized conductor fit into the lugs there are mac adapters available.

Charlie please also note that when converting to MC please keep in mind the the fault calculations may change to increase the available AIC rating.

If this is a new project? Could new lugs be ordered to accomadate for the MC?

 

[coulter]

edit (Wow it worked)

test to see if I can post a link

http://forums.mikeholt.com/showthread.php?t=79963&highlight=Okonite

(Rest of edit)

Some types of MC let you use the sheath as part of the grounding conductor. 250.118(10) 250.122(A)

Okonite CLX (MC-HL) is the only one that I am familiar with. There are other brands that also comply.

Okonite's website has most of the data you need, but as I recall, it is missing the piece that gives the effective CU area of the sheath - which you also need - I got it from the rep.

As I recall, you are right at the edge for 4 - 350.

I'll find my paper and send it - could take me a day.


carl