Another sub panel question

[Bryan]

Good morning, I inspected an apartment complex under renovation yesterday where they are replacing some of the breaker sub panels. The original panels were three wire ran underground in EMT from the meter/disconnect to the sub. The new panels are set up the same way except they have added a fourth conductor as a ground to the near by copper water line. My question, is the water line connected conductor adequate to serve as the equipment ground or should they have installed an additional conductor back tot the disconnect? My initial thought process was no it is not adequate; however, I wanted to post to be sure. There is also other problems with the panel such as mixed grounds and naturals.

Thanks in advance

Bryan

Click to Enlarge

77.91 KB

[esch]

If your speaking of what I think of as a cold water ground, It was used alot and actually only code (they said no on driving rods, I dont know why) in Athens, Texas. But from my experience the cold water ground corrodes through the pipe (copper) and leaks (about 10-15 years normally)

[Billy_Bob]

With a new installation generally, you would need 4 wires going from a subpanel back to the main panel (two hots, a neutral, and a ground). And the subpanel neutral bonding screw removed.

But then there are "existing installations" which might fall under different rules in certain situations???

This is all up to local rules. Best to check with your local electrical inspector. Local states/areas can modify the rules to be anything they want.

(I personally think the 4 wire system is the safest.)

Then in *my* opinion, cold water pipe grounds are no longer good grounds. This is because everyone tends to replace water pipes these days with plastic PVC pipe when doing repairs.

So is all the existing cold water piping still all metal? Or has someone replaced sections of it with plastic?

And will someone at some future time replace sections of the metal pipe with plastic? And will they at that time be sure to move the ground connections to a good ground?

So far as the local electrical inspector goes, using the cold water pipe might be perfectly OK! (Again these rules are local, so ask the inspector...)

[Richard Moore]

My question, is the water line connected conductor adequate to serve as the equipment ground...

No, it's an unreliable path at best, and totally inadequate if the piping is not also bonded at the service disconnect.

or should they have installed an additional conductor back tot the disconnect?

I assume they used to use the EMT as the grounding conductor, which is OK. Any reason they can't still use it?

With the mixed grounds and neutrals and the two ground/neutral bars tied together in the sub-panel, I would have to wonder if this was ever right. It certainly isn't now and it doesn't seem that the renovation sparky knows what the hell he's doing.

[Bryan]

Thanks for the information so far.To answer a few more questions /comments, the copper water line extends through the floor slab in the middle of the unit. Therefore, who know where it goes or what its composition is once it goes underground, I can only assume it is all copper given the 35-40 year age of the building.

The grounding clamp on the water lines appears to be original given the paint build up on the clamp; however, the grounding wire is new.

The EMT conduit should run back to the disconnect and may have been used originally for the ground. However, when sparky upgraded, the fitting and lock nut were not installed tight or with a jumper wire bonded to the new panel.

I think at a minimum the ground and natural conductors need to be isolated. The sad part is this panel has pasted the city inspection.

Bryan

[Richard Moore]

I think at a minimum the ground and neutral conductors need to be isolated.

I wouldn't want to put it like that. If that's all they do then you may end up with an unreliable or inadequate path to the utility grounded conductor, which means that a short or ground fault in a circuit might not trip that circuit's breaker.

The rules for this "sub-panel" set-up are fairly simple, haven't really changed that much, and I doubt they differ in any significant way from one jurisdiction to the next.

1: The panel should have a floating neutral bar with all neutrals, and only neutrals, connected to it.

2: The grounding bar should be separate and properly bonded to the panel. All grounding conductors should go to that.

3: A reliable, continuous, grounding conductor should go to the service equipment (panel/disconnect). That could be the original EMT (at this stage it would be wise to test that) or an added conductor, but not the water piping. (Note that I have no objections to the connection to the water piping from the sub-panel, but it should only be considered as bonding of the metallic piping and not the actual grounding.)

4: The neutrals and grounds should be bonded at the service equipment which should be properly connected to grounding electrodes.

[Jim Katen]

Good morning, I inspected an apartment complex under renovation yesterday where they are replacing some of the breaker sub panels. The original panels were three wire ran underground in EMT from the meter/disconnect to the sub. The new panels are set up the same way except they have added a fourth conductor as a ground to the near by copper water line. My question, is the water line connected conductor adequate to serve as the equipment ground or should they have installed an additional conductor back tot the disconnect?

Well, right off the bat, there's some difficulty with 300.3(B) which says that all conductors of the same circuit, including equipment grounding conductors are all supposed to be kept together.

My initial thought process was no it is not adequate; however, I wanted to post to be sure.

Well, on first reading, the only place I see where you can run your equipment grounding conductors to a water pipe is 250.130©, which only applies to the replacement of non-grounding receptacles or branch circuit extensions. Even then, the only part of the water piping that you can use is the part that's within the first 5' from where it enters the building. (250.52(A)(1))

The general rule is at 250.130(A), which says that the connection "shall be made by bonding the equipment grounding conductor to the grounded service conductor and the grounding electrode conductor." That means it has to go back to the service disconnect.

I'd say that what they did is screwy.

- Jim Katen, Oregon