Equipment Grounding Conductor b/n xfmr and service disco

[sceepe]

For a commercial facility, is an equipment grounding conductor required to be run in the service lateral between a utility pad mounted xfmr and the service disconnect? I have seen it done both ways. You can assume the grounded service conductor is installed per 250.24. Voltage system may be 3 phase 277/480V or 120/208V. Also, the grounding electrode conductor is connected to neutral in the service disconnect.

Second question, if the service is supplied via overhead drop from pole mounted xfmrs, is an equipment grounding conductor required to be run with the service entrance conductors between the service point and the service disconnect. If no, how is the meter case grounded (by conduit?)?

Thanks in advance

 

[bennie]

Re: Equipment Grounding Conductor b/n xfmr and service disco

There are many threads concerning these questions.

A short answer is; No.

To install an equipment ground conductor, at these locations, will only increase the impedance of the fault path.

[ March 16, 2004, 10:19 AM: Message edited by: bennie ]

 

[charlie]

Re: Equipment Grounding Conductor b/n xfmr and service disco

Most electric utilities prohibit a grounding conductor from the premises wiring system to be connected to their grounding system. That would be putting the grounding conductor in parallel with the grounded conductor.

The metering equipment and everything else in front of the service equipment is generally grounded to the MGN (multi-Grounded Neutral from the utility service or grounded conductor in the NEC language).

 

[rasmithircgov.com]

Re: Equipment Grounding Conductor b/n xfmr and service disco

I believe no. Using 250.24(B)I think you would be parraleling the grounded service entrance conductor because it would originate and end at the same location.

 

[pierre]

Re: Equipment Grounding Conductor b/n xfmr and service disco

Charlie
If the fourth conductor as mentioned in this thread (EGC) is installed with the service conductors, and is terminated separately from the grounded conductor at the service equipment, there would be no parallel current flow (such as a 'subpanel'). Of course the grounded conductor should be insulated.

Pierre

 

[rasmithircgov.com]

Re: Equipment Grounding Conductor b/n xfmr and service disco

Pierre, I see what your saying. What would be the benefit? I couldn't see why a contractor would add such a cost and how the system would be safer by installing one. Your not installing a bonding or equipment bonding jumper. The grounded service entrance conductor takes care of this.What Art. could be used to allow this to be installed.Looking for information.

[ March 17, 2004, 08:55 AM: Message edited by: rasmithircgov.com ]

 

[bennie]

Re: Equipment Grounding Conductor b/n xfmr and service disco

Changing to a smaller conductor for a fault path, is counter to the code requirement for lowest impedance fault path.

I feel that adding an equipment ground conductor is a code violation.

 

[charlie]

Re: Equipment Grounding Conductor b/n xfmr and service disco

Pierre, how would you satisfy 250.24(A)? You are going to have the grounding electrode conductor connected to the grounded service conductor at the service.

 

[eprice]

Re: Equipment Grounding Conductor b/n xfmr and service disco

I hope I am not hijacking this thread, but it reminds me of a similar situation that I had to deal with a few months ago, and have never been completely satisfied with the outcome.

The scenario was a CT metering cabinet located at the street near the poco transformer. There was no service disconnect at that location. The service entrance conductors ran underground in PVC to the service disconnect at the building some distance away. The CT cabinet was isolated from the neutral. The poco insisted that it could not be bonded to the neutral. They said it would mess up the CT metering and they would not connect if the cabinet was bonded to the neutral. I tried to convince them that bonding to the neutral was the proper way, but to no avail. The only way we could get the CT cabinet bonded was to have a bonding conductor ran back through the conduit from the service disconnect. The poco didn't seem to be bothered by the fact that if a fault to ground occured at the CT cabinet, the current would have to follow the bonding conductor through the conduit all the way to the service disconnect, hitch a ride on the neutral and come all the way back befor finding its way to the transformer which was just a few feet away from the cabinet.

 

[bennie]

Re: Equipment Grounding Conductor b/n xfmr and service disco

When there is no overcurrent device, to clear a fault at the CT can, an added impedance may not be so bad.

 

[charlie]

Re: Equipment Grounding Conductor b/n xfmr and service disco

Eprice, someone at that electric utility had their head where it didn't belong. Besides violating the NEC, it violates NESC Rule 093.