I have a few questions on whether or not the following situation sounds code compliant:
A service is provided with 3 phases and a grounded conductor (multigrounded neutral system). The cables are brought to switchgear which has a main bonding jumper connecting the neutral bus and ground bus per NEC 250.186(A). The neutral bus is connected to the ground grid. One feeder section in the medium voltage gear feeds a delta-wye (resistance grounded secondary) with the NGR on the secondary also connected to the same ground grid.
Another feeder section in the switchgear feeds an existing wye-wye (solidly grounded) transformer a little ways away. The H0/X0 are internally connected. This used to be utility owned, but is now going to be client owned. The wye-wye transformer enclosure and the H0/X0 are connected to a ground rod. There are three existing PVC conduits, which the client wants to reuse, feeding the transformer. Each conduit has one phase conductor with a concentric neutral. The conductors are going to be replaced with new 25 kV Southwire UD EPR cable. NEC 300.5(I) Exception 2 allows isolated phase installation because the conductors are installed in non-metallic conduit and the UD EPR cable doesn't have a magnetic sheath.
I am not very familiar with multigrounded neutral systems, but am following NEC 250.184(C). The concentric neutral will act as both the neutral and the EGC, correct? Does 250.190(C)(2) still apply?
I don't believe the NEC has any issue internally connecting H0 and X0 to ground on the existing transformer.
Are there any issues connecting the medium voltage gear to the same ground grid as the secondary of the delta-wye transformer? I briefly read an article about multigrounded neutral systems being hazardous due to stray currents.
A service is provided with 3 phases and a grounded conductor (multigrounded neutral system). The cables are brought to switchgear which has a main bonding jumper connecting the neutral bus and ground bus per NEC 250.186(A). The neutral bus is connected to the ground grid. One feeder section in the medium voltage gear feeds a delta-wye (resistance grounded secondary) with the NGR on the secondary also connected to the same ground grid.
Another feeder section in the switchgear feeds an existing wye-wye (solidly grounded) transformer a little ways away. The H0/X0 are internally connected. This used to be utility owned, but is now going to be client owned. The wye-wye transformer enclosure and the H0/X0 are connected to a ground rod. There are three existing PVC conduits, which the client wants to reuse, feeding the transformer. Each conduit has one phase conductor with a concentric neutral. The conductors are going to be replaced with new 25 kV Southwire UD EPR cable. NEC 300.5(I) Exception 2 allows isolated phase installation because the conductors are installed in non-metallic conduit and the UD EPR cable doesn't have a magnetic sheath.
I am not very familiar with multigrounded neutral systems, but am following NEC 250.184(C). The concentric neutral will act as both the neutral and the EGC, correct? Does 250.190(C)(2) still apply?
I don't believe the NEC has any issue internally connecting H0 and X0 to ground on the existing transformer.
Are there any issues connecting the medium voltage gear to the same ground grid as the secondary of the delta-wye transformer? I briefly read an article about multigrounded neutral systems being hazardous due to stray currents.