I have a group (3) of 480v, 3 phase 1500kw Generators feeding a data center. These Gen sets are located outside, in a fenced area, within enclosures. They feed to a 4000 amp paralleling gear and on to 4000 amp switchgear. The feeders to the gear are properly grounded and bonded back at the service entrance and in the switchgear. The Gen sets are properly grounded ( service grounds);however, the frame of the Gen sets are not bonded to the generator or to an earth driven ground. I want to insure that the I do not create a hazardous location, protect against lighting strike and create a proper drain. Am I legal according to NEC , in providing an earth driven ground at each Gen set location to accomplish properly bonding the Gen set frames.
Generator Bonding
- Thread starter conroe
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Re: Generator Bonding
Can you elaborate on "The Gen sets are properly grounded ( service grounds)". Tell us how this occurs.
As a side note, are these separately derived sources? Meaning, is the transfer between utility and paralleling gear a three pole or four pole transfer, and is their a neutral to ground bond at the generators.
Can you elaborate on "The Gen sets are properly grounded ( service grounds)". Tell us how this occurs.
As a side note, are these separately derived sources? Meaning, is the transfer between utility and paralleling gear a three pole or four pole transfer, and is their a neutral to ground bond at the generators.
- Location
- Bremerton, Washington
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- Master Electrician
Re: Generator Bonding
The answer to your question depends on how the generator transfer switch works. Are the generators a separately derived system with a 4 pole transfer switch or do they have a 3 pole transfer switch with solid neutral.
See definition of Separately derived system and section 250.30.
Also review the definitions of grounded and equipment grounding conductor. What do you mean when you say the generator is grounded? Are you referring to the grounded conductor or the equipment grounding conductor? For this question its important to know.
[ December 03, 2003, 11:31 AM: Message edited by: tom baker ]
The answer to your question depends on how the generator transfer switch works. Are the generators a separately derived system with a 4 pole transfer switch or do they have a 3 pole transfer switch with solid neutral.
See definition of Separately derived system and section 250.30.
Also review the definitions of grounded and equipment grounding conductor. What do you mean when you say the generator is grounded? Are you referring to the grounded conductor or the equipment grounding conductor? For this question its important to know.
[ December 03, 2003, 11:31 AM: Message edited by: tom baker ]
Re: Generator Bonding
Let me better explain the senario.The gen sets are 1250kw( not 1500 kw) 480v,3 phase, 4 wire, wye
output. Center tap ground. It feeds the generator paralleling gear, which also contains the utility power. This breaker feeds the generator bus (paralleling gear)) that ties into the main switchgear in the building and generator bus. In the event of a power loss, the main utility breaker opens and the generator breaker closes (all manual). A redundant manually operated main breaker from the generator bus provides an alternate source to the main gear in the building. This redundant main is kirk-key interlocked to prevent closing both breakers at the same time. There is no ATS for this installation. The main switch gear in the building is main-tie-main configuration. Neutrals are not switched anywhere, they are solid connections. Grounding conductors are solidly connected back to the 4000 amp service entrance to the building, where grounding electrodes are installed. Does this answer your questions?
Let me better explain the senario.The gen sets are 1250kw( not 1500 kw) 480v,3 phase, 4 wire, wye
output. Center tap ground. It feeds the generator paralleling gear, which also contains the utility power. This breaker feeds the generator bus (paralleling gear)) that ties into the main switchgear in the building and generator bus. In the event of a power loss, the main utility breaker opens and the generator breaker closes (all manual). A redundant manually operated main breaker from the generator bus provides an alternate source to the main gear in the building. This redundant main is kirk-key interlocked to prevent closing both breakers at the same time. There is no ATS for this installation. The main switch gear in the building is main-tie-main configuration. Neutrals are not switched anywhere, they are solid connections. Grounding conductors are solidly connected back to the 4000 amp service entrance to the building, where grounding electrodes are installed. Does this answer your questions?
Re: Generator Bonding
Connect the generator star point to the frame of the stator. This will contain an internal ground fault to the interior of the generator, and prevent the current from appearing on other conductors.
The phase failure relays will see the fault and dump the exciter.
[ December 04, 2003, 09:33 AM: Message edited by: bennie ]
Connect the generator star point to the frame of the stator. This will contain an internal ground fault to the interior of the generator, and prevent the current from appearing on other conductors.
The phase failure relays will see the fault and dump the exciter.
[ December 04, 2003, 09:33 AM: Message edited by: bennie ]
Re: Generator Bonding
Since the neutral is not switched, the generator is not a separately derived system. There is a direct electrical connection between the normal grounded system conductor and the generator neutral. Therefore the generator neutral is not required to be grounded again. You will need to remove the bonding connection between the generator neutral and the frame. The frame will be grounded by the system GEC. I you wish to install a ground rod, it must be bonded to the generator frame.
[ December 04, 2003, 03:32 PM: Message edited by: bob ]
Since the neutral is not switched, the generator is not a separately derived system. There is a direct electrical connection between the normal grounded system conductor and the generator neutral. Therefore the generator neutral is not required to be grounded again. You will need to remove the bonding connection between the generator neutral and the frame. The frame will be grounded by the system GEC. I you wish to install a ground rod, it must be bonded to the generator frame.
[ December 04, 2003, 03:32 PM: Message edited by: bob ]
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