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#58181 - 11/01/05 09:50 PM Increased EGC size  
Redsy  Offline
Joined: Mar 2001
Posts: 2,056
Bucks County PA
250.122(B) requires EGCs to be increased proportionally when circuit conductors are increased for voltage drop.
So, although a #10 EGC is good enough for up to a 60 amp ckt., per Table 250.122, if you run a particularly long, 20-amp ckt. and increase the ungrounded conductors to, say #8, you will need to increase the EGC to #8 also.
Any comments, please?

Work Gear for Electricians and the Trades

#58182 - 11/01/05 10:00 PM Re: Increased EGC size  
iwire  Offline
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
You summed it up nicely.

Bob Badger
Construction & Maintenance Electrician

#58183 - 11/01/05 10:52 PM Re: Increased EGC size  
Redsy  Offline
Joined: Mar 2001
Posts: 2,056
Bucks County PA
I'm wondering why a #10 ground is good enough for a 60-amp ckt with #6 circuit conductors, but not good enough for a 20-amp ckt. with #8 circuit conductors.

#58184 - 11/02/05 12:59 AM Re: Increased EGC size  
PCBelarge  Offline
Joined: Jun 2003
Posts: 681
Dobbs Ferry, NY, USA
Effective Ground Fault Current Path

Pierre Belarge

#58185 - 11/02/05 07:55 AM Re: Increased EGC size  
Redsy  Offline
Joined: Mar 2001
Posts: 2,056
Bucks County PA

If #10 is effective for a 60 amp OCPD, why not for a 20 amp OCPD. I don't believe that the increased resistance due to length will inhibit the operation of the CB.
And if the EGC and circuit conductors need to be matched in size for some concept related to balanced, or equal impedances between circuit conductors and EGCs, why can the EGC be smaller than the circuit conductors in circuits above 30-amp?

#58186 - 11/02/05 08:13 AM Re: Increased EGC size  
resqcapt19  Offline
Joined: Nov 2000
Posts: 2,148
How would you write the rule? The EGC does have to increase with the size of the ungrounded conductors, and I don't know of a way to write a rule to accomplish this other than how it is currently written. If you do, it is not too late to submit an online proposal .


#58187 - 11/02/05 08:48 AM Re: Increased EGC size  
Redsy  Offline
Joined: Mar 2001
Posts: 2,056
Bucks County PA
Thanks, guys.

I am just wondering if there is some kind of theoretical concept that I am overlooking?

#58188 - 11/02/05 12:25 PM Re: Increased EGC size  
C-H  Offline
Joined: Sep 2002
Posts: 1,497
Stockholm, Sweden
From a theoretical point of view you want the impedance of the PCBelarge's effective ground fault current path to be low enough to trip the breaker within a reasonable time.

If the 20A breaker is designed to be very forgiving to momentary surges in current while the 60A breaker so to speak is "trigger happy", you could get this counterintuitive result. The breaker manufacturers or their websites can no doubt tell.

[This message has been edited by C-H (edited 11-02-2005).]

[This message has been edited by C-H (edited 11-02-2005).]

#58189 - 11/02/05 12:50 PM Re: Increased EGC size  
gfretwell  Offline

Joined: Jul 2004
Posts: 9,103
I understand the concept but the reality is 2000 feet of #12 would still trip a 20a breaker with a bolted fault, even if it takes 150% (30a) to operate it.

Greg Fretwell

#58190 - 11/02/05 02:10 PM Re: Increased EGC size  
John Crighton  Offline
Joined: May 2005
Posts: 177
Southern California
gfretwell: Yes, the breaker would trip. But in the meantime, the voltage at the point of fault would be higher than if the EGC was sized per the rule, so the shock threat is greater.

Redsy: I know it sounds inconsistent, but I don't think it is. Remember, the reason the EGC was sized up was the long run. If that 60 amp circuit was the same length, it would need a #4 EGC.

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