Subpanel Wiring Method

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kar108

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A 100 amp subpanel for an addition is wired with SE cable from the main panel to the 100 amp breaker in the subpanel. The subpanel neutral bar is isolated from the panel and grounded to a ground rod with #6 bare copper. Grounds are terminated on the neutral bar. I see several problems here:
(1)The feeder wire to the subpanel requires an insulated neutral.
(2) A grounding conductor is required from the main panel to the subpanel which must be in the same cable or raceway as the conductors.
(3) The neutrals and grounds should be separated with a grounding terminal bar.

I think the SE feeder cable should be replaced with either 4 conductor SER cable with or 4 individiual THHN insulated conductors in conduit to take care of items 1 & 2.

Two questions --
1) Am I on the right track with 1,2,and 3 above?

2) Is there any problem leaving the #6 bare ground connected from the subpanel grounding bar to a ground rod?
 
Re: Subpanel Wiring Method

If the bare in the SE is being used as the neutral, and if the neutrals and grounds are isolated from one another at the sub panel you have a very dangerous installation.

The way it is now a fault to ground will not trip a breaker.

The ground rod is not hurting anything but it is also not helping anything.

By the way, is the addition a separate building or just an addition to the existing?
 
Re: Subpanel Wiring Method

Bob,
The bare wire in the SE cable is the neutral -- the neutrals and grounds are currently on the same terminal block in the subpanel. Are you saying that separating the neutrals and grounds will create an unsafe condition or that they need to be separated to remedy an unsafe condition?

The addition is an attached mother-in-law apt. to an existing building.
 
Re: Subpanel Wiring Method

I think I heard about an electrocution in a trailer park or something a year or so ago where the fault path was a ground rod and the fault, instead of clearing, only energized everything.
 
Re: Subpanel Wiring Method

The grounded conductor terminal block should be isolated.

There should be both a grounded conductor and EGC back to the main panel.

Editted because of too many letters.

[ January 11, 2005, 07:14 PM: Message edited by: physis ]
 
Re: Subpanel Wiring Method

sounds like the sub-panel was the service equipment panel at one time. grounding & grounded
conductors cannot be together load side,
250.24 (A) (5), I would check & make sure that the grounding electrodes are in the main panel & not the sub-panel & change the cable to SER.
 
Re: Subpanel Wiring Method

The sub panel would require a four wire installation, separate Grounded and Grounding conductors. If using SE cable, they make a 4 wire cable.

The grounded conductor(aka Neutral) will be insulated and the bar will be isolated from the panel board. This is where all the white or gray wires attach. The grounding conductor, bare or green, attaches to the panel ground bar and all ground wires (bare or green) will connect there.

As far as the grounding electrode wire goes, it can be bare or insulated, but it connects to the ground bar, not the neutral bar on a sub panel.
 
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