Grounding of residential subpanel

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don_resqcapt19

Moderator
Staff member
Location
Illinois
Re: Grounding of residential subpanel

pb,
I think that, if I were the AHJ, I'd permit a remote EGC for a feeder with a 70 amp OCPD. I don't think that the additional impedance caused by the fault clearing path being remote from the feeder will have any great effect on the fault clearing time of this circuit. If the circuit OCPD was larger, over 200 or 300 amps, I would not approve the remote EGC.
As far as the hazard level, of this installation there is a potential for harm. This is not much different from the 3 wire circuits that were permitted for many years on stove and dryer branch circuits. In these circuits a single conductor served as both the grounded and grounding conductor. There were proposals made over 3 or 4 code cycles before the rule was changed to require 4 wire circuits. All of the proposals cited the "potential" problems that could occur when using a single conductor for both functions. The CMP asked for any evidence of a problem that had really occurred. I don't recall anyone citing an actual real world problem that was caused because of the use of a 3 wire circuit.
Don
 

pbunge

Member
Location
California
Re: Grounding of residential subpanel

Don
I appreciate your reasoning as being anchored in real life. Respectful of the intent of the code to ensure safety and yet not wasting time, effort and money to chase down potential risks that exist more in theory than real life.

Please confirm that I am hearing you right. Add an EGC and bond to the new panel, no bonding to a water pipe common to other units. Bond ground and neutrals together on the same buss bar as was done in the old panel.

Peter
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Re: Grounding of residential subpanel

pb,
Run a new equipment grounding conductor from the subpanel to the main panel and connect directly or indirectly to the grounded conductor at the main panel. Connect the other end to an equipment grounding bus in the subpanel. Keep the grounding and grounded (neutrals) separate in the subpanel. A bond to the a water pipe from the subpanel equipment grounding bus would be fine. Please note that this is not a code compliant installation!! I feel that it is safer than the existing installation and I would permit it if I was the AHJ. The AHJ would be well within his rights to insist on a new feeder with an equipment grounding conductor from the main panel to the subpanel as this is what the code requires.
Don
 
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