Undersize Ground Wire

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GirlieElectrician

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Boston
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Electrical Estimator/Project Manager
I need help with the following:
Pulled 275' of 600A parallel MC feeders, it was supposed to be (4#350/1#1G) but just found out it's #4G. I need a solution rather than re-pulling the wire and what would be acceptable under code. I'm at my end whits here.
 
I don't know that there is a fix in your particular situation other than repulling. Maybe 250.122(F)(2)(b) would apply?
 
GirlieElectrician said:
None of the above, its an MC Cu Feeder, supported by strut and clips. going from the basement and up to 5th floor thru corridors and chase.
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OH I thought MC meant motor control.
Does 350 Kcmil feeder MC cable not just come with #3 EGC?
 
No, it did not. it came with a #4G instead of the #1G (Which I originally ordered). We are tapping the existing SWBD bus because the 600A SWBD BKR didn't have room space in the front of the switchgear. The designer in the record in turn decided to have us tap the bus, and feed into a 600A disconnect so it can provide power to a 600A/3P panel located on the 5th floor.
 
tortuga said:
OH I thought MC meant motor control.
Does 350 Kcmil feeder MC cable not just come with #3 EGC?
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The issue is that when you use a cable wiring method for a parallel circuit, the EGC in each of the paralleled cables will not be large enough to comply with 250.122(F), unless you order custom cable.
 
winnie said:
Would it be acceptable to use the _undersized_ EGCs built into each cable combined with an additional EGC of sufficient size?

Jon
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Not without a written special permission from the AHJ. I might consider that if the MC has an aluminum jacket, but not if it has a steel jacket.

Also might consider permitting it with GFPE on the feeder OCPD, with a ground fault trip setting less than 100 amps.
Some old codes had a provision like this, but required the ground fault protective device to be specifically listed for the protection of the EGC and there was no device so listed.
 
Does 250.122(F)(2)(c) apply to MC cables? It doesn't apply directly to the OP's installation, only to 'multiconductor cables' in 'the same raceway, auxiliary gutter, or cable tray'. But it would seem to apply indirectly unless 250.122(F)(2)(c) doesn't apply to MC cables.

Thanks
Jon
 
winnie said:
Does 250.122(F)(2)(c) apply to MC cables? It doesn't apply directly to the OP's installation, only to 'multiconductor cables' in 'the same raceway, auxiliary gutter, or cable tray'. But it would seem to apply indirectly unless 250.122(F)(2)(c) doesn't apply to MC cables.

Thanks
Jon
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Seems like a reasonable solution route a #1 (or larger) up there and closely follow the MC. Still would need special permission.
 
winnie said:
Does 250.122(F)(2)(c) apply to MC cables? It doesn't apply directly to the OP's installation, only to 'multiconductor cables' in 'the same raceway, auxiliary gutter, or cable tray'. But it would seem to apply indirectly unless 250.122(F)(2)(c) doesn't apply to MC cables.

Thanks
Jon
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MC is a multiconductor cable and would apply if the OPs two cables were in the same raceway or were installed in a common cable tray.
 
don_resqcapt19 said:
MC is a multiconductor cable and would apply if the OPs two cables were in the same raceway or were installed in a common cable tray.
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Agreed. 250.122(F)(2)(c) presumably does not directly apply.

But say I have MC clamped to a strut trapeze and then pulled through a vertical chase with undersized EGCs in the cable. I'd point to 250.122(F)(2)(c) when asking the AHJ for permission to use a properly sized external EGC in the analogous situation.

-Jon
 
Just to summarize:

At the supply end you don't have room for additional OCPD, so you tapped the supply at its ampacity.
The run is MC clipped to strut, then in a chase for part of the run.
The run is 2 parallel MC cables, 4x350+1x#4 per cable.
The inspector has already said that an external (to the MC) properly sized EGC is not code compliant.

Other than formally asking the inspector to reconsider, I've got nothing.

-Jon
 
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