# 4 wire versus 3 wire subfeed



## 480sparky (Sep 20, 2007)

In a 4-wire feed, the only time the ground carries current is during a fault.


----------



## Cirus (Jun 23, 2012)

Yea, I know that. I'm talking about an imbalance in the main panel resulting in a backfeed to the subpanel. Will it not also backfeed on the ground wire to the subpanel? Whats to stop it from backfeeding on both ground and neutral wires since they are bonded together in the main panel?


----------



## Shockdoc (Mar 4, 2010)

The GEC landed in the main panel is supposed to take that current.


----------



## brian john (Mar 11, 2007)

Cirus said:


> Yea, I know that. I'm talking about an imbalance in the main panel resulting in a backfeed to the subpanel. Will it not also backfeed on the ground wire to the subpanel? Whats to stop it from backfeeding on both ground and neutral wires since they are bonded together in the main panel?


Not sure what you are asking or if you are very confused.

If you have a 3 phase 4 wire system and have a sub panel downstream from the main service with the neutral bonded to ground per the NEC.

So assume have imbalance load on the phase conductors the imbalance will be on the neutral. This current cannot get on the Equipment Ground Conductor (EGC) (copper or metallic as there is no connection at the sub panel (assuming the installation is NEC compliant). The current will return to the source up stream to the generator or transformer not downstream towards the load.

If you mean something else, please post.


----------



## 480sparky (Sep 20, 2007)

Cirus said:


> Yea, I know that. I'm talking about an imbalance in the main panel resulting in a backfeed to the subpanel. Will it not also backfeed on the ground wire to the subpanel? Whats to stop it from backfeeding on both ground and neutral wires since they are bonded together in the main panel?



It needs a place _to go_ in order for current to flow. IOW, a circuit needs to be formed first.


----------



## Dennis Alwon (May 9, 2009)

I believe the Op is talking about a single phase with a ground and neutral isolated at the sub panel.

I think he is asking if there is current on the neutral at the sub panel what stops it from flowing to the ground wire since they are connected together at the main panel.

Current is flowing back to the source. What would make the current flow from the main panel back to the egc on the sub panel. They are isolated and the current would have to loop in circles -- there would be too much impedance for that to happen.


----------



## Shockdoc (Mar 4, 2010)

Sounded to me as if the OP leaned toward a lost main noodle situation on where the imbalance goes.


----------

