generator neutral grounding

[murli]

I am wiring a 3 phase GENSET through a Transfer switch. The utility power comes to the other end of the transfer switch. The utility feed is 3 phases, 3 wire, 480VAC. The loads are all 3 phases motor loads. No single phase loads.
QUESTION: Do I need to ground the neutral of the GENSET. ? Since the utility is running ungrounded, can I run the generator ungrounded ?
It makes no sense to have 2 different systems, one with the utility system ungrounded and the other GENSET system grounded.
The code says that if you have single phase loads, you must have the neutral grounded.
Also this installation is not in public area and is accessable only to qualified electricians.

 

[tom baker]

Re: generator neutral grounding

The location and who services the generator does not matter for the installation.
Need to know the following:
1. Is this a delta system from the utility? If so is it a corner grounded delta? (think about how the fault current gets back to the utility transformer in the event of a line to case fault)
2. What type of transfer switch is it, three pole or 4 pole.
Please review the defintion of seperatly derived system and all of 250.30
And make sure you see the difference between a grounded neutral conductor and the equipment grounding conductor. For a service they are combined into one conductor. For a generator, even with no neutral loads, a means must be provided to get the fault current from a line to case fault back into the generator windings.

 

[dereckbc]

Re: generator neutral grounding

I had to edit my first post. If your service is a open ungrounded Delta you have three options:

1. Leave the generator as a ungrounded system. Bond the genset frame to the GES via bonding jumper. If you use this option you will need some sort of GFD and GFP to protect generator.

2. Bond the grounded circuit conductor to the GES via GEC, and install a MBJ between the grounded circuit conductor and genset frame to configure the genset as SDS.

3. Use high resistance grounded system on genset.

[ February 01, 2004, 04:36 PM: Message edited by: dereckbc ]