#6 Copper Wire as Groun for 100A?

[Joel 67]

For a 100A panel (#2 THHN for both hot wires, as well as netural), do I need a #6 or a #8? I am reading different things on different sites and want to do this correctly.

 

[sberry]

100A requires 8, but 6 wont hurt a thing.

 

[JBurgess]

100A requires 8, but 6 wont hurt a thing.

I have only once have an inspector reject #8 on a 100 amp feed using #2 wire, citing 250.122 (B) requiring the ground wire to be increased in size since #2 is an increase in size over the #3 required. But he was a jerk. Every other inspector was good with the #8



250.122 (B) Increased in Size. Where ungrounded conductors are
increased in size, equipment grounding conductors, where
installed, shall be increased in size proportionately according
to the circular mil area of the ungrounded conductors.

 

[Aceman]

I have only once have an inspector reject #8 on a 100 amp feed using #2 wire, citing 250.122 (B) requiring the ground wire to be increased in size since #2 is an increase in size over the #3 required. But he was a jerk. Every other inspector was good with the #8



250.122 (B) Increased in Size. Where ungrounded conductors are
increased in size, equipment grounding conductors, where
installed, shall be increased in size proportionately according
to the circular mil area of the ungrounded conductors.

I figured some cranky inspector would take advantage of that article when #2 was used. It seems most electricians use it for 100 amps, fortunately our inspector seems to let it slide. I try to use #3 as much as possible now though, I don't want to find out the hard way and fail an inspection.

 

[sberry]

Thanks, I was wondering if using 2 made the jump to 6 required, I use 6 anyway for rods.

 

[Norcal]

I figured some cranky inspector would take advantage of that article when #2 was used. It seems most electricians use it for 100 amps, fortunately our inspector seems to let it slide. I try to use #3 as much as possible now though, I don't want to find out the hard way and fail an inspection.

"Cranky" inspector? That is a inspector doing their job, code is code, and if not enforcing 250.122(B) they are not doing their job.

 

[Aceman]

Yes, I understand code is code.

I can't be sure, but I don't believe CMP's intention was to require upsize grounds just because you felt like running #2 to a 100 amp panel 20 feet away. But rather if you were running #2 due to VD issues. You can say code is code all day long if it helps you, but if an inspector were to pop me for it on a short run I'd probably think he couldn't find anything better to cite. Just my personal opinion...

 

[JBurgess]

Yes, I understand code is code.

I can't be sure, but I don't believe CMP's intention was to require upsize grounds just because you felt like running #2 to a 100 amp panel 20 feet away. But rather if you were running #2 due to VD issues. You can say code is code all day long if it helps you, but if an inspector were to pop me for it on a short run I'd probably think he couldn't find anything better to cite. Just my personal opinion...

Sometimes I wonder if the inspector gets a kickback from the re-inspection fees.

If you use 60 degree lugs then the #8 ground with the #2 conductors is OK, but you are limited to 95A calculated load.

Many times I can get #2 cheaper than #3 due to the quantities involved.

 

[Norcal]

I got into a stink on that very subject at a home inspectors forum, a poster argued that one was not required to do so, he emailed the NFPA (Publishers of the NEC), here is a copy & paste of the email.

From: Cloutier, Mark [mailto:[email protected]]
Sent: Tuesday, December 22, 2009 10:19 AM
To:
Cc: [email protected]; Johnston, Michael; Henderson, Carol
Subject: RE: NEC 250.122 (Log #29202)MC

To:
Date: 12/22/09

This is in reply to your email concerning the National Electrical Code®. The NFPA electrical staff cannot approve a particular design or arrangement, comment on workmanship issues, review or perform calculations for compliance. Issues of compliance are the responsibility of the Authority Having Jurisdiction, but I can provide some general remarks.

Section 250.122(B) requires an equipment grounding conductor (EGC) on the load side of an overcurrent device to be increased in size wherever the associated ungrounded conductors are increased in size. The increase in size of the EGC must be done proportionately according to the circular mil area of the ungrounded conductors. Once the ungrounded conductors are increased in size for whatever reason deemed necessary, 250.122(A) is no longer applicable and the requisite requirements of 250.122(B) are required.

Mark Cloutier
NFPA Senior Electrical Engineer

Important notice! This correspondence is not a Formal Interpretation issued pursuant to NFPA Regulations. Any opinion expressed is the personal opinion of the author, and does not necessarily represent the official position of the NFPA or its Technical Committees. In addition, this correspondence is neither intended, nor should be relied upon, to provide professional consultation or services.
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I did edit out the orig recipient info, all other text is unchanged.