Scooter250
Member
- Location
- Los Angeles
I have an industrial facility with a 1200 service. The user's needs require a dual ended main board to allow the facility to be powered from portable/temporary generator in the event of prolonged power outage. This is not emergency power or any other type of backup power that is code required. Both "main" breakers are 1200A and require ground fault protection. The connection and safety interlocks between the two power sources are all taken care of an approved by the inspector, but the ground fault protection is yet to be signed off on.
The generator is to be installed so that it is not a separately derived system, i.e. the neutral is not switched (3 wire transfer system consisting of interlocked breakers) and the generator neutral is not bonded at the generator - the bonding jumper is only provided at the main board. My understanding is that this creates issues with ground fault current paths that lead to improper sensing and tripping of the GF system. I also believe that using a 4 wire transfer system would eliminate problems about fault current paths, however this approach is undesirable for reasons that are owner driven. I am looking for a correct ground fault scheme for this application.
Does anybody out there have any experience with this level of detail in ground fault protection? Simply providing a GFI with each main breaker does not resolve the problem as far as the inspector is concerned. What is the correct approach, or is a 4 wire transfer system the only way to go?
The generator is to be installed so that it is not a separately derived system, i.e. the neutral is not switched (3 wire transfer system consisting of interlocked breakers) and the generator neutral is not bonded at the generator - the bonding jumper is only provided at the main board. My understanding is that this creates issues with ground fault current paths that lead to improper sensing and tripping of the GF system. I also believe that using a 4 wire transfer system would eliminate problems about fault current paths, however this approach is undesirable for reasons that are owner driven. I am looking for a correct ground fault scheme for this application.
Does anybody out there have any experience with this level of detail in ground fault protection? Simply providing a GFI with each main breaker does not resolve the problem as far as the inspector is concerned. What is the correct approach, or is a 4 wire transfer system the only way to go?
