Grounding Old Main Panel, Locating Grounding Rods

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Benhear

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We have replaced a subpanel in a very old electrical system that has no ground to the main panel and no grounding rod(s). Long story short -- we are not now upgrading the main panel and have no convenient location to install the ground rods at that location.

I'm thinking that I run a new ground wire to the main panel from our new subpanel, connect this to the existing neutral bar there, but run the ground rods from the subpanel location. Assuming that all the grounds are connected but still floating (separate from the neutrals) at the subpanel location, is there any problem with this setup?

Should of taken a pic of the existing main panel ... its quite something ... I'll try and get some Monday

Thanks
 
thanks for the welcome

no separate structure ... main outside the building goes to the subpanel inside
 
The GEC for the grounding electrode must land in the main panel where the MBJ is installed.
 
infinity said:
The GEC for the grounding electrode must land in the main panel where the MBJ is installed.
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Rob, that is not correct. You are probably thinking of an SDS. Service GEC can connect anywhere from service point to service equipment.

250.121 does not allow an EGC to be used also as a GEC, however it has an exception stating if both requirements are met, then it is acceptable.
 
electrofelon said:
Rob, that is not correct. You are probably thinking of an SDS. Service GEC can connect anywhere from service point to service equipment.

250.121 does not allow an EGC to be used also as a GEC, however it has an exception stating if both requirements are met, then it is acceptable.
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The OP wants to land the GEC in a sub-panel but yes I meant to say must not land beyond the main panel. It can land anywhere upstream. I could have stated that better. :oops:
 
Thanks much I think I get it now. What's an SDS by the way? If that GEC has to run 25 or 30 feet would I need to increase wire size?
 
Also, after a quick read on the exceptions allowed in 250.121, I'm a little unclear. Can somebody offer a sketch/description of a layout of a set up that would actually meet all of the requirements for GECs and EGCs and thus be acceptable under the exception.... in other words a real example of what would work.
 
thanks again ... I know what I need to do for this one

... but in the interest of my ongoing education .... the 250.121 exception. Was wondering if something like this would work: An 8 gauge ground runs continuously from a 100A main panel MBJ to a water spigot that comes straight out of the ground; from here, an 8 gauge wire jumps to two separate ground rods and another 8 gauge wire jumps from the water pipe to the sub-panel to provide the equipment grounds.

sorry to belabor the point

--B
 
Benhear said:
thanks again ... I know what I need to do for this one

... but in the interest of my ongoing education .... the 250.121 exception. Was wondering if something like this would work: An 8 gauge ground runs continuously from a 100A main panel MBJ to a water spigot that comes straight out of the ground; from here, an 8 gauge wire jumps to two separate ground rods and another 8 gauge wire jumps from the water pipe to the sub-panel to provide the equipment grounds.

sorry to belabor the point

--B
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Equipment Grounding Conductor has to be ran in the same conduit or cable as the circuit conductors.
 
Two separate issues: adding a proper GEC to the main, and getting an EGC to the subpanel.

In general an EGC needs to run in the same conduit or raceway as the circuit conductors. There are some exceptions, and I am not up on the details of the current code, but it used to be that you could ground a previously ungrounded circuit by running an EGC to an accessible GEC. Perhaps this would apply here.

In other words, install a new GEC from the main, that happens to go near to the subpanel, possibly even following near to the subpanel feeder conductors, and then run an 'upgrade' EGC to this GEC?

-Jon
 
Yes, 250.130C seems to allow an EGC that is separate from the circuit conductors in a retrofit situation.
 
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ActionDave said:
There have been a couple of on again off again code changes where egc and gec were allowed to be the same conductor. Maybe I'm misremembering where we are at currently.
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OK, I missed that the OP said there was no EGC to the sub, hence the confusion.
Benhear said:
Yes, 250.130C seems to allow an EGC that is separate from the circuit conductors in a retrofit situation.
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You can not use that for a feeder, that is for branch circuits. I am not aware of any exception to the "same raceway or cable" requirement for your situation :(
 
Yes, I see the distinction you make between a feeder and branch circuit but I don't see the rationale. Is there a technical reason for why the ground must run with the conductors on feeders (but not necessarily on branches)?

All this time I thought I could resolve my ungrounded sub-panel situation by running just a new properly sized EGC from the main panel while leaving the existing wires intact. Now that the "same raceway or cable" requirement has come up, I see that that might not be permissible.
 
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