Ground Fault Protection Feeders/SDS
Ground Fault Protection Feeders/SDS
(OP)
In most areas of the USA, the NFPA 70 (NEC) is code.
Section 215.10 requires ground fault protection for feeders that are "1000 amperes or more and installed on solidly grounded wye electrical systems of more than 150 volts to ground, but not exceeding 600 volts phase-to-phase" unless "ground-fault protection of equipment is provided on the supply side of the feeder" etc.
The following examples are not services, but feeders:
If there was GFP on the primary of a delta-wye solidly grounded transformer (1000kVA, 480/277V secondary, separately derived source), would you consider the feeder on the secondary side of the transformer GF protected on it's supply side?
Is your answer the same if the input feeder to a 1000kVA dual conversion type UPS module, 480/277V output, separately derived source, is protected upstream by GFP? Is the output feeder of the module GF protected on it's supply side?
Section 215.10 requires ground fault protection for feeders that are "1000 amperes or more and installed on solidly grounded wye electrical systems of more than 150 volts to ground, but not exceeding 600 volts phase-to-phase" unless "ground-fault protection of equipment is provided on the supply side of the feeder" etc.
The following examples are not services, but feeders:
If there was GFP on the primary of a delta-wye solidly grounded transformer (1000kVA, 480/277V secondary, separately derived source), would you consider the feeder on the secondary side of the transformer GF protected on it's supply side?
Is your answer the same if the input feeder to a 1000kVA dual conversion type UPS module, 480/277V output, separately derived source, is protected upstream by GFP? Is the output feeder of the module GF protected on it's supply side?






RE: Ground Fault Protection Feeders/SDS
RE: Ground Fault Protection Feeders/SDS
If Power in = Power out + losses, then the primary would have to "see" the fault.
RE: Ground Fault Protection Feeders/SDS
Draw yourself a diagram of the windings of a delta-wye transformer and trace the current flow for a phase-to-ground fault on the wye side. You will see that all of the current is in one or the three windings on the secondary. With current in only one winding on the secondary there will only be current on one winding in the primary and in the delta that current is phase-to-phase. No unbalanced current for a ground fault sensor to detect. Conservation of kVA is maintained.
RE: Ground Fault Protection Feeders/SDS
What davidbeach says. A ground fault on a transformer secondary will be seen on the primary as either a load or an overcurrent, not as a ground fault.
respectfully
RE: Ground Fault Protection Feeders/SDS
Ground fault current is sometimes calculated as large as bolted phase fault depending on the impedance of the ground conductor.
RE: Ground Fault Protection Feeders/SDS
RE: Ground Fault Protection Feeders/SDS
RE: Ground Fault Protection Feeders/SDS
In a critical environment, it is typical to have to make coordination/selectivity decisions based on reliability vs. equipment protection.
RE: Ground Fault Protection Feeders/SDS
RE: Ground Fault Protection Feeders/SDS
With that said, when dealing with certain occupancies, and certain design priorities, sometimes I need to abide by the absolute minimum code.
That is why I was trying to get opinions regarding the varied interpretation of the NEC article 215.10 Exception#3 "ground-fault protection of equipment is provided on the supply side of the feeder".
RE: Ground Fault Protection Feeders/SDS
RE: Ground Fault Protection Feeders/SDS
A feeder is:
All circuit conductors between the service equipment, the source of a separately derived system, or other power supply source and the final branch-circuit overcurrent device.