I have been asked to look at an installation involving 3 standby generators at a hospital. The generators are 1135 kw each with 2000 amp circuit breakers installed on the end of each generator. The generators are in a common "generator building" located approximately 350 feet away from the main hospital building. Cable trays have been installed between the generators and the emergency paralleling switchgear within the hospital's main switchgear room. On each cable tray are parallel runs of MC Cable (4 #500mcm and 2 #4 grounds). Each generator has its own cable tray. Additionally the cable tray and fittings are listed for grounding. Additionally a bare copper ground has been installed the entire length of the cable tray. The generator case has been grounded to the building steel within the generator building. Additionally, the bare copper ground from the cable tray has been connected to the generator case. Neutral to ground bonding takes place at the emergency switchgear (not at the generator). Is this a proper installation. I feel the neutral to ground bond should take place at the generator or first overcurrent device (which would be within the generator building and not at the emergency switchboard). Other information - 4 pole transfer switches are used downstream, so I think this constitutes a separately derived system. Additionally, the 2000 amp breakers at the generators do not have ground fault protection. Neither do the 2000 amp breakers within the emergency switchgear. Since it's emergency power, I don't think it advisable to have GF trip on these breakers. I am puzzled as how the bonding meets code. Should I have the generators bonded at each set and remove the factory bond at the emergency switchgear?
Generator Neutral bonding
- Thread starter khkn1598
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- Status
- Location
- Illinois
- Occupation
- retired electrician
Re: Generator Neutral bonding
The installation appears to be correct and code compliant. When a 4 pole transfer switch is used only one point of bonding is permitted. 250.32 does not permit multiple bonding for these two buildings because there is an EGC run with the feeder. Per 700.26, GFP is not required, but ground fault indication is.
Don
[ August 31, 2004, 09:44 PM: Message edited by: don_resqcapt19 ]
The installation appears to be correct and code compliant. When a 4 pole transfer switch is used only one point of bonding is permitted. 250.32 does not permit multiple bonding for these two buildings because there is an EGC run with the feeder. Per 700.26, GFP is not required, but ground fault indication is.
Don
[ August 31, 2004, 09:44 PM: Message edited by: don_resqcapt19 ]
- Location
- Illinois
- Occupation
- retired electrician
Re: Generator Neutral bonding
My previous post is not correct. I don't know what I was thinking last night. The use of a 4 pole transfer switch requires that a bonding connection be made at the service and a second one for the SDS. And you are correct that the generator bonding connection must be between the generator and the first OCPD.
Don
My previous post is not correct. I don't know what I was thinking last night. The use of a 4 pole transfer switch requires that a bonding connection be made at the service and a second one for the SDS. And you are correct that the generator bonding connection must be between the generator and the first OCPD.
Don
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