What would you do with the equipment grounding conductor for a new branch circuit (small appliance circuit) that will originate at a subpanel supplied via a three-wire feed (no grounding conductor)?
The feeder to the subpanel originates in a subpanel (formerly the house main panel) that is itself supplied by a three-wire feeder from the new service panel.
1) install a GFCI, not connect the branch ckt ground (EGC), and label the outlet "no equipment ground"? 2) land the branch ckt EGC on the grounded (neutral) bus at the subpanel, after checking the integrity of the neutral back to the service entrance? 3) install an EGC bus and set up the neutral bus as a floating bus in the subpanel from which the new circuit will originate, and run an EGC back to the service entrance? 4) other?
The problem I see with #2 is that if the neutral back to the service entrance were to be disconnected or damaged, the EGC of the new circuit could wind up carrying up to full line voltage.
In contrast, if a service neutral is lost, the grounding electrode system will provide some degree of return for the current. Has anyone ever run across a situation where the service neutral was lost, and the grounding electrode impedance was high, causing a dengerous voltage to be impressed on the equipment grounding conductors?
I see the problem with #3 being the amount of time it would take.
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I would install a ground bar in the sub panel and isolate the neutrals from the EGC. You should be able to ground to the nearest cold water pipe and make sure (or add) the water pipe is attached to a supplemental ground rod. There's no nee to go back to the meter. I would repeat this for the other sub panel also.
Re: new ckt to old subpanel#26459 06/13/0304:54 AM06/13/0304:54 AM
There are two subpanels (in series). There was originally the main panel and a sub, then the house was added onto, and a new service was installed. So the former main panel became sub 1 and the sub became sub 2.
There is no floating neutral terminal bar in subpanel 2, I think because it is old (50's, maybe). Although I recall someone on this forum once asked when the requirement that the neutral and ground be separated except at the service, and I recall the reply being 1949 or earlier. And sub 1 doesn't have a floating neutral bar because it was formerly the main. And none of the circuits have equipment grounding conductors (EGCs), anyway.
At any rate, sub 2 is a zinsco, in good shape. And I have a good stock of old Zinsco breakers from panel replacements and old house teardowns.
I don't know if it'd be practical to run an EGC back to the service and add a floating neutral bar to sub 1 and sub 2. It certainly wouldn't be cost-effective. If the client wants to upgrade the other circuits to have EGCs, I'll recommend replacing the panels.
What I'll do for the small appliance circuit that triggered my question is leave the EGC unconnected at both ends and mark the GFI receps "no equipment ground".
Thanks again for the input.
Re: new ckt to old subpanel#26463 06/16/0311:32 PM06/16/0311:32 PM
I think I know where you're going with this--if thre's a raceway and it's steel, we've got a 4-wire feed and so could isolate the neutrals at sub 1, then run an EGC to sub 2 and isolate the neutrals there! Right?
Unfortunately, the feeder from the main to sub 1 is three-wire romex, and the feeder to sub 2 is thre-wire as well, old rag-and-tar romex (about the diameter of a garden hose!) At least all the feeders are copper!
I considered running an EGC from sub 2 back to the service panel, and separating the neutrals, but I'm not sure that sub 2 has the room in it to add a floating neutral bar.
I'm going to go with the "no equipment ground" labelling option. It's truly the most cost-effective approach.
Thanks much for spending the time--
Re: new ckt to old subpanel#26465 06/17/0307:31 AM06/17/0307:31 AM
Cliff, If this is a new branch circuit, you don't have the option of using a non-grounded, GFCI protected receptacle. The exceptions that permit this only apply to the replacement of a two wire receptacle or to the extension of an existing two wire branch circuit. The only code compliant options that you have are to run a new 4 wire feed to the sub-panel or run the new branch circuits back to the service panel. Don
Re: new ckt to old subpanel#26466 06/17/0307:42 AM06/17/0307:42 AM
If one of the sub panels were to be corrected, all four conductors would have to be ran back to the main panel, correct? You wouldn't be allowed (I think) to run a ground conductor to a water pipe and go to a ground bus in the panel(sub), and just run 2 hots and a nuetral back to the main. It must be a big house, if you don't want to bring a ckt. back to the main panel.