Current present on GEC

[Frank D]

We have a client with current on the GEC. The facility has 2 480V 3 phase 3,000A services, each fed by a separate utility transformer.
Service 1 has a current (it varies + or - 10%) present on the GEC of 4.5 amps.
Service 2 has a current (it varies + or - 10%) on the GEC of 25 amps.
The site is a resort, with service 1 providing most of the mechanical equipment, and service 2 providing most of the 120 volt loads, the hotel rooms and some small mechanical equipment.
Understanding that the GEC should not have constant current present, and that there has been only minimal work done since the original construction, I haven’t found any evidence of a design flaw, and have not found the culprit.
The interesting part, is that the current is respective to the proportion of the single pole loads. The majority of the 1 pole loads are on service 2, with the highest ground current.
Comments welcome.

 

[infinity]

Wha type of electrode is the GEC connected to? A small amount of current on the GEC is normal for something like a water pipe electrode.

 

[Frank D]

Ground sys is rebar grid, building steel, water supply, it is probably as low impedance as possible.

 

[don_resqcapt19]

water supply

Is the water supply piping common to other facilities that have electrical power?

 

[ptonsparky]

I would expect more current flow on this.

Ground sys is rebar grid, building steel, water supply, it is probably as low impedance as possible.

Can you measure the flow on each connection?

 

[Frank D]

Is the water supply piping common to other facilities that have electrical power?

The ground system is all bonded at a single point, water, rebar net, building steel. No other power system is connected, the system is all in a single building.

I would expect more current flow on this.

Can you measure the flow on each connection?

My understanding up to this point was that there should not be any significant current flow on the GEC. You mentioned you would expect more current flow, I’m guessing you have run into this before. Where do you believe it is originating from? And is this normal?
I can’t measure it at each location because the majority of the distribution is via bus duct with bus plugs feeding panels and transformers. Were the ground was accessible such as a disconnect I did measure and found no significant current. All of the single pole loads whether 277 or 120 current levels are balanced, with the unbalanced current in the proper amperage on the neutral. 14A, 12A, 26A, N 12A

 

[Little Bill]

The ground system is all bonded at a single point, water, rebar net, building steel. No other power system is connected, the system is all in a single building.

He is asking if there are other buildings, structures, etc, that are not part of the property your job is on, that shares a water supply source and also has an electrical supply.
Example: A group of apartments, houses, businesses, etc, down the road, and not part of your property, that has power, and has the same water supply that you have.

 

[Elect117]

Make sure they didn't use the EGC as a neutral for the lighting packs / circuits and for some receptacles. Sometimes it is as simple as they thought the equipment was 3W and it actually needed a neutral for controls. And they just used the EGC for it.

Turn off dry types (if any) to narrow it down or turn off single pole breakers one at a time. If it is 3ph and not handle tied, expect it to fluctuate until you have turned off all of the MWBCs. Amp clamp hots and neutrals. If you have 5 A on the hot and 15A on the neutral or 5A on the hot and 3A on the neutral you have found where the last guys messed up. Sometimes you can measure the EGC for a given circuit as well. But that isn't as good of a metric on finding the issue circuit(s). You can sometimes have so many parallel paths that the current on the wire type EGC is lower than the conduit or building steel. Especially when the EGC wire size is small.

Building steel and cold water are bonded to the EGC at multiple points. Typically everywhere there is EMT, RMC, or equipment that is mounted to the building steel, has a copper water pipe on it, etc.

I recently ran into a place that had lazy electricians using the EGCs as neutrals and what started the investigation was a small amount of current on the building steel and ~4 to 10V on open breakers (phase to EGC) and circuits at different places. They also messed up wiring the battery packs for each emergency light. And lastly, they didn't handle tie. It was a mess to sort out. Thankfully all I had to do was diagnose. The electrician had to scissor lift and find all of it.

You would honestly be surprised at the drop off in quality of work in the LA area. A lot of these guys come from out of state and just want to get back home. The ol' "looks good from my house" stuff. So just assume the last guy was brain dead.

 

[don_resqcapt19]

The ground system is all bonded at a single point, water, rebar net, building steel. No other power system is connected, the system is all in a single building.

I am asking if the water supply piping also supplies water to buildings other than yours?

 

[Joethemechanic]

I'm picturing this as separate buildings, each supplied by it's own padmount. And the buildings are connected with a common metallic piping system?

How far apart are the transformers? I'm thinking about the length of the path along the MGN. Or more down to the point.. impedance along the MGN

 

[ptonsparky]

I'm picturing this as separate buildings, each supplied by it's own padmount. And the buildings are connected with a common metallic piping system?

How far apart are the transformers? I'm thinking about the length of the path along the MGN. Or more down to the point.. impedance along the MGN

Single building, but guessing more than one stepdown xfmr.

 

[Joethemechanic]

Single building, but guessing more than one stepdown xfmr.

I've seen this a lot in philly. Older industrial buildings broken up for multipal occupancy, each occupant with their own service drop and maybe different pole pigs. I've seen a quite a bit of difference in potential between the neutrals. I never really went out to a place because of a problem with it, but where the N or G got close enough to another service for the leads on my Simpson 260 to reach, I tested.

 

[Frank D]

Is the water supply piping common to other facilities that have electrical power?

Clarification: The service power for this building has dedicated transformers (2) that do not feed any other facility. The water supply is connected to the main supply pipe from the local water district and serves a large downtown commercial area, it is old, and likely a very large pipe. There is not likely any current flowing towards the switchgear from an outside source.

 

[Frank D]

Single building, but guessing more than one stepdown xfmr.

There are two transformers dedicated for this building only. My concern and the purpose of this thread would be to get input from the field on whether or not this level of current on the GEC is normal, or acceptable, and any explanation of why this current is present would be greatly welcomed. We have tested the grounds on Transformers, the neutral loading at most of the main panel distribution systems. It will be extremely impractical to try and do this at the circuit level as there’s several thousand circuits in the building. Also, we don’t have the liberty of shutting power down.