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#58181 - 11/01/05 05:50 PM Increased EGC size
Redsy Offline
Member
Registered: 03/28/01
Posts: 2056
Loc: 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?
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#58182 - 11/01/05 06:00 PM Re: Increased EGC size
iwire Offline
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Registered: 01/05/03
Posts: 4391
Loc: North Attleboro, MA USA
You summed it up nicely.
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#58183 - 11/01/05 06:52 PM Re: Increased EGC size
Redsy Offline
Member
Registered: 03/28/01
Posts: 2056
Loc: 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.
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#58184 - 11/01/05 08:59 PM Re: Increased EGC size
PCBelarge Offline
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Registered: 06/08/03
Posts: 681
Loc: Dobbs Ferry, NY, USA
Effective Ground Fault Current Path
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Pierre Belarge
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#58185 - 11/02/05 03:55 AM Re: Increased EGC size
Redsy Offline
Member
Registered: 03/28/01
Posts: 2056
Loc: Bucks County PA
PCB,

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?
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#58186 - 11/02/05 04:13 AM Re: Increased EGC size
resqcapt19 Offline
Member
Registered: 11/10/00
Posts: 2148
Loc: IL
Redsy,
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 .
Don
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#58187 - 11/02/05 04:48 AM Re: Increased EGC size
Redsy Offline
Member
Registered: 03/28/01
Posts: 2056
Loc: Bucks County PA
Thanks, guys.

I am just wondering if there is some kind of theoretical concept that I am overlooking?
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#58188 - 11/02/05 08:25 AM Re: Increased EGC size
C-H Offline
Member
Registered: 09/17/02
Posts: 1497
Loc: 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).]
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#58189 - 11/02/05 08:50 AM Re: Increased EGC size
gfretwell Offline


Member
Registered: 07/20/04
Posts: 9039
Loc: Estero,Fl,usa
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.
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Greg Fretwell
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#58190 - 11/02/05 10:10 AM Re: Increased EGC size
John Crighton Offline
Member
Registered: 05/16/05
Posts: 177
Loc: 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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