No EGC In Generator Subpanel

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wvda79

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Hi all!
I recently found this site and see some very knowledgeable people post here. I?ve been looking for a site like this for some sound advice on a project I?ve been working on where I?ve been getting conflicting answers.
Here?s the scenario:

I?ve been asked to put into service a 200 amp sub-panel off of a 150kw generator that has it?s own structure that also houses the main disconnect, main panel and automatic transfer switch. The system is setup non SDS , (does not switch neutral) and 120/208V 3ph.
The neutral on the generator is not bonded to generator frame.
The sub-panel is in a separate building located about 50yds away that was installed but never was put into service about 15 years ago. It is a 200A, 3ph panel..

Here?s the problem:
When I opened the panel, I discovered that there were 3 phase conductors, 1 neutral but no EGC conductor. The conductors are directly buried in the ground from the generator building to the sub-panel building, so pulling in an EGC is out of the question. I thought about just wiring this panel single phase and using one of the phase conductors as the EGC. This would not be much of a problem, as there is only going to be a small load on this panel, but it would leave 1/3 of the panel dead.
I consulted with others on this problem and was told I could just re-ground the neutral with the equipment ground in this panel just like a new service as long as there are no conductive metallic paths between the two buildings. Then I was told I couldn?t do this because since the neutral is not being switched, it is necessary to install an EGC conductor.
There is yet another 1ph 100A sub-panel being fed from this 200A sub-panel going to another building that was not supplied with an EGC. This is a main lug panel that I assume will have to be replaced with a main breaker panel.

I?ve have tried to provide as many details as possible but if any other info. is needed please ask.
All comments, opinions and advice will be greatly appreciated as I need to get started on this soon.
 
Re: No EGC In Generator Subpanel

Since the circuits you are concerned with are emergency circuits I need to ask if there are non emergency feeders or branch circuits to these same buildings. If yes then there are other metallic pathways between the buildings and you will have to invest the effort to install Equipment Grounding conductors.

If the generator supplied feeders are the only supply to the buildings in question then you can bond the neutral to the building disconnecting means and install the required Grounding Electrode System at each building. Since the code specifically permits the grounding of the neutral at separate buildings that do not have other metallic pathways between them there is no problem with the fact that the neutral is no switched because it would be grounded in the same two places under both emergency and utility supply.
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Tom Horne
 
Re: No EGC In Generator Subpanel

This system is covered in 702 Optional Standby
Systems. The grounding of the generator is discussed in 702.10(B). It resuires that you install an equipment grounding conductor for the existing electrical system. The fact that you may or may not have metallic pathways has nothing to do with this installation. If you ground the neutral with a ground rod then you will have the neutral tied to 2 different grounding electrodes.

[ August 12, 2004, 10:43 PM: Message edited by: bob ]
 
Re: No EGC In Generator Subpanel

Thanks for your input guys. I'm anxious to see what other opinions will be.
 
Re: No EGC In Generator Subpanel

Originally posted by bob:
This system is covered in 702 Optional Standby
Systems. The grounding of the generator is discussed in 702.10(B). It requires that you install an equipment grounding conductor for the existing electrical system. The fact that you may or may not have metallic pathways has nothing to do with this installation. If you ground the neutral with a ground rod then you will have the neutral tied to 2 different grounding electrodes.
Click to expand...
Bob
How is it that you think that 702.10 (B) applies to this situation? How did you come to the conclusion that the generator in question was portable?

702.10 Portable Generator Grounding.
(A) Separately Derived System. Where a portable optional standby source is used as a separately derived system, it shall be grounded to a grounding electrode in accordance with 250.30.
(B) Nonseparately Derived System. Where a portable optional standby source is used as a nonseparately derived system, the equipment grounding conductor shall be bonded to the system grounding electrode.

On what are you basing the idea that the rules on Two or More Buildings or Structures Supplied from a Common Service that are found in 250.32 do not apply? The section I refer to specifically permits the Grounded Current Carrying Conductor that most of us call the neutral conductor to be bonded to the grounding electrodes available at each building if there are no other conductive pathways between the buildings and no Equipment Grounding Conductor is run with the circuit conductors.

250-32. Two or More Buildings or Structures Supplied from a Common Service
(a) Grounding Electrode. Where two or more buildings or structures are supplied from a common ac service by a feeder(s) or branch circuit(s), the grounding electrode(s) required in Part C of this article at each building or structure shall be connected in the manner specified in (b) or (c). Where there are no existing grounding electrodes, the grounding electrode(s) required in Part C of this article shall be installed.
Exception: A grounding electrode at separate buildings or structures shall not be required where only one branch circuit supplies the building or structure and the branch circuit includes an equipment grounding conductor for grounding the noncurrent-carrying parts of all equipment.
(b) Grounded Systems. For a grounded system at the separate building or structure, the connection to the grounding electrode and grounding or bonding of equipment, structures, or frames required to be grounded or bonded shall comply with either (1) or (2).
(1) Equipment Grounding Conductor. An equipment grounding conductor as described in Section 250-118 shall be run with the supply conductors and connected to the building or structure disconnecting means and to the grounding electrode(s). The equipment grounding conductor shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded. Any installed grounded conductor shall not be connected to the equipment grounding conductor or to the grounding electrode(s).
(2) Grounded Conductor. Where (1) an equipment grounding conductor is not run with the supply to the building or structure, and (2) there are no continuous metallic paths bonded to the grounding system in both buildings or structures involved, and (3) ground-fault protection of equipment has not been installed on the common ac service, the grounded circuit conductor run with the supply to the building or structure shall be connected to the building or structure disconnecting means and to the grounding electrode(s) and shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded.
--
Tom Horne

[ August 20, 2004, 03:20 PM: Message edited by: hornetd ]
 
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