MC Cable Ground Size

[jcook980]

The 2002 also had a listed for the purpose requirement.

Nope, it simply required it to be listed. Check the wording in the 2002 Code carefully. The way it was worded then, any listed ground fault device was acceptable. The committee re-wrote that section to require the ground fault device to be specifically listed to protect the EGC. Since that is never going to happen, the edit effectively eliminates this means of protecting the EGC.

Here's the 2005 ROP:

5-231a Log #CP504 NEC-P05
(250-122(F)(2)3)
Final Action: Accept
Submitter: Code-Making Panel 5
Recommendation:
In 250.122(F)(2)(3) Change the words "listed for the purpose" to "... listed for the purpose of protecting the equipment grounding
conductor."
Substantiation:
The panel revised the text to remove vague unenforceable term " ? for the purpose ?", improve clarity, and comply with the NEC Style
Manual 3.2.1.
Panel Meeting Action: Accept
Number Eligible to Vote: 16
Ballot Results: Affirmative: 16
Comment on Affirmative:
SKUGGEVIG: Correlation with Proposal 5-1 regarding changing the term "equipment grounding conductor" to "equipment bonding
conductor" will be needed.

 

[iwire]

Nope, it simply required it to be listed.

Not quite.

In my 2002 NEC book top left of page 70-115

It says exactly this.

(3) The Ground-fault protection is listed for the purpose.

The change in 2005 is really not a change in the requirment only a change in the wording to make clear what the purpose is.

Take a look at the ROP you posted.

Change the words "listed for the purpose" to "listed for the purpose of protecting the equipment grounding conductor."

Substantiation:
The panel revised the text to remove vague unenforceable term " ? for the purpose ?", improve clarity, and comply with the NEC Style

 

[LarryFine]

. . . improve clarity, and comply with the NEC Style . . .

Well, which one?

 

[cpal]

This is from the 08 pre print if this language holds the comment process you better use theGFPE real soon

250.12 (F) Conductors in Parallel. Where conductors are run in
parallel in multiple raceways or cables as permitted in
310.4, the equipment grounding conductors, where used,
shall be run in parallel in each raceway or cable. [ROP
5?287]
Each parallel equipment grounding conductor shall be
sized on the basis of the ampere rating of the overcurrent
device protecting the circuit conductors in the raceway or
cable in accordance

 

[necnotevenclose]

Well I met with the rep and it appears he is just as confused as I'am. He said that to meet 250.122(F) you could use a 900-900-900-900-900 (which I guess is a standard item) and use fewer runs to achieve 4000A with an oversized ground. But then I have to think are the lugs going to be capable of accepting 900kcmil.

The rep did mention he was going to look into this further and get back to me. So if I hear anything I will be sure to post it.

 

[iwire]

nec, I appreciate you getting back to us on this.

I really do not understand why on such a costly installation you are using the manufacturer as a designer.

There is no confusion, the NEC clearly requires us to follow 250.122(F) in all paralleled installations.

 

[coulter]

I use a lot of Okonite 600V, CLX, welded aluminum, corrugated sheath, with copper conductors. It's type MC-HL.

I just happened to do some research on MC-HL and grounding, Nov 2004, so this is based on the 2002 code.

The code allow the use of the sheath as part of the grounding conductor. See NEC 250.118(11) and UL 1569.

Okonite does not publish all of the required conductor data in their CLX Product Data Sheet. One must also look at the CLX Cable Handbook.

Rockbestos Gardex MC cable product data sheet shows similar construction to Okonite CLX. The sheath thicknesses and diameters are similar to CLX. However, I haven't seen their cable handbook.

As for southwire, I heard from a reliable source, they delivered within the last two years, a large order (multiple semi loads) of what looks like MC-HL, all multi-conductor, small sizes. I did see some, and it is stamped "Southwire", and looks like MC-HL. So they are likely geared up to produce for all.

As for specifics on effective conductor area for grounding, the only one I remember is 3c-750 has sheath + grounding conductors = 250kcmil CU. I don't have a code book here, but I suspect that is still too small for 4000A with paralleled 750.

carl