3 Wire bonded at sub panel serving 30 amp 125 v. R.V.recepticals

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FWD

Member
This situation came to my attention when a shock was reported.The pre 1986 feeders connected to a sub panel are 3 wire direct burial with no ground conductor.A ground rod was driven at the sub panel.The equipment ground conductors were terminated in the panel under a single lug to the enclosure.The neutral was not bonded.A short occurred and the panel, all of the R.V. receptacle enclosures,ground terminals came live.I disconnected the short circuit and bonded the neutral to the panel enclosure.The complete installation is in violation,I understand that the sub panel has to be replaced.I understand that a 4 wire system is required under the current code.But is this 3 wire system grandfathered or am required to replace it with a 4 wire?I am leaning toward replacing the entire underground run in order be in compliance with the current code.Not sure what was required in the past, Most references pertaining apply to a detached garage.Any help would be appreciated!
 

drcampbell

Senior Member
Location
The Motor City, Michigan USA
Occupation
Registered Professional Engineer
It sounds like you've already answered your own question.

If there aren't any 240-volt loads, you could avoid excavating by converting the existing cable to a three-wire 120-volt-only configuration.
 

Chamuit

Grumpy Old Man
Location
Texas
Occupation
Electrician
I believe most jurisdictions require you to bring anything you touch up to the current code cycle they are on....
 

user 100

Senior Member
Location
texas
This situation came to my attention when a shock was reported.The pre 1986 feeders connected to a sub panel are 3 wire direct burial with no ground conductor.A ground rod was driven at the sub panel.The equipment ground conductors were terminated in the panel under a single lug to the enclosure.The neutral was not bonded.A short occurred and the panel, all of the R.V. receptacle enclosures,ground terminals came live.I disconnected the short circuit and bonded the neutral to the panel enclosure.The complete installation is in violation,I understand that the sub panel has to be replaced.I understand that a 4 wire system is required under the current code.But is this 3 wire system grandfathered or am required to replace it with a 4 wire?I am leaning toward replacing the entire underground run in order be in compliance with the current code.Not sure what was required in the past, Most references pertaining apply to a detached garage.Any help would be appreciated!

250.32(B) exception lets you keep the feeder, but still talk to your ahj- some will let you slide on this- only panel replacement and let you keep the existing feeder, some won't. Imo best to just replace the feeder if you can- it's decades old, direct buried, and it's removal may prevent issues. I don't agree with the suggestion of dropping the 3 w to 120- there may not be 240 loads now, but there could be in the future....

As for the detached garages reference and applicability, 250.32 applies to buildings and "structures", and the definition of structures in art 100 is ridiculously broad, so it's likely that whatever your subpanel is attached to is a structure.:)
 
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FWD

Member
Thanks all,since there are no parallel paths I will probably keep the feeder and replace the panel.As i understand it,wire it the same as a main panel with two ground rods?May add CFCI circuit breakers.
 

euclid43

Senior Member
I agree and it is what I would do.
I think there's mention 250.32B(1)(2) if there are no continuous metal paths between the two bldgs. I think you have to make sure that there is no water lines that may be in use for bonding.....
 
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