How do I ground an existing subpanel?

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Old 08-18-12, 03:53 PM
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How do I ground an existing subpanel?

I have a 1950s ranch with a 50A subpanel without a ground. The subpanel is wired with three #6 without a ground. The subpanel is about 70 ft from the main. Can I run a seperate ground from the main to the sub, following the same path as the #6-3? If I ran a seperate ground, it would not be in a conduit, it would just run parallel to the current feed. Or should I run a new #6-3G.
 

Last edited by Nashkat1; 08-18-12 at 04:15 PM.
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Old 08-18-12, 04:54 PM
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The subpanel is about 70 ft from the main.
It sounds, at that distance, like the subpanel is in a detached structure, but I'd like to be clear. Is it in a separate building, or is it at the opposite end of an unusually long house from your main distribution panel?
 
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Old 08-18-12, 07:36 PM
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The subpanel is in the house, just at the opposite end of a long ranch so no grounding rod required (correct?). What's interesting (or maybe scary) is that the ground and neutrals are already seperated / isolated in the subpanel (each has it's one bus). So the ground bus really isn't grounded. I'll run a #10 ground from the main to the sub. Thanks.
 
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Old 08-18-12, 08:29 PM
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The EGC, separate ground bus, and isolated neutral is required by modern code but no ground rod. The EGC (equipment grounding conductor) wire can be run anyway that is convenient. It must connect to the main ground. If this is a 60 amp feed #10 green or bare is all you need. Of course it is grandfathered but always good to bring it up to modern code.
 
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Old 08-18-12, 08:36 PM
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The subpanel is in the house, just at the opposite end of a long ranch so no grounding rod required (correct?).
Correct.

What's interesting (or maybe scary) is that the ground and neutrals are already seperated / isolated in the subpanel (each has it's one bus).
That the neutrals and the grounds are terminated to separate bus bars does not mean that the neutrals are isolated. Isolated, in this case, means "electrically and mechanically isolated from the subpanel enclosure and from all other phases." What that means, in practice, is that the neutral bus must be mounted on insulating legs and that there cannot be any screw or other means bonding it to the can.

At the same time, the grounds must be bonded to the enclosure and to earth. That means that the ground bus needs to be in direct contact with the can and, should be bonded to it with an approved ground screw, and should have an EGC (an Equipment Grounding Conductor) from the main panel terminated to it.

So the ground bus really isn't grounded.
If there's no ground rod with a conductor between it and the ground bar in the panel, establishing a separate grounding electrode, and there isn't and EGC run between the main and this subpanel, then no, it isn't.

I'll run a #10 ground from the main to the sub.
Please do, A.S.A.P. And do any other work needed to bond the enclosure to ground while isolating the neutrals.
 
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Old 08-19-12, 06:59 AM
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The subpanel is in the house, just at the opposite end of a long ranch so no grounding rod required (correct?). What's interesting (or maybe scary) is that the ground and neutrals are already seperated / isolated in the subpanel (each has it's one bus). So the ground bus really isn't grounded. I'll run a #10 ground from the main to the sub.
So, you are saying the 60 amp feeder to the subpanel is an open cable and not run in metal conduit?
 
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Old 08-19-12, 08:13 AM
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What is the wiring method between the two panels?
 
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Old 08-19-12, 04:42 PM
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Thanks guys. Just to summarize for the follow up question. Just bought a house with a subpanel in the basement that was feed with #6-3 NM no ground and not in conduite; just run under the floor joist. The neutral bus was isolated from the ground and can (no bonding screw and confirmed with resistance reading with feed disconnected) while the ground bus was bonded to case. I wanted to make sure the subpanel was grounded, but wasn't certain if I could run a seperate ground or if I needed to run a new #6-3G. As suggested, I ran a seperate ground. All is good. Thanks for the help and for followup questoins/carlifications.
 
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Old 08-19-12, 06:28 PM
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Glad you got it. Thanks for letting us know.
 
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