iamtodd4160
Member
OK, I have a unique system that needs to be as safe as possible as soon as possible (yes i know right and soon don't mix well). we have transformers (from 300KVA to 2MVA) 11Kv to 230/400 V that feed a panel with a main and sub breakers these sub breakers feed buildings or another sub panel that will in turn feed a building (these panels are located outside and are unguarded). All structures receive 3 phases and of course have a neutral conductor (grounded conductor). There is no real start or end of the "service". Right now there are very few of these that have an equipment ground conductor. The current answer to this problem is to make sure that the neutral (grounded conductor) is bonded until a equipment grounding wire is used (inside the buildings). This does make sense as ground fault protection but couldn't there be a good chance of touch potential on the boxes (since bonding will occur at all of them except at the internal box of the building). The NEC allows this for separate buildings that do not have the extra wire run to use as the equipment ground.
I feel that an equipment ground wire should be run from the first breaker box after the transformer and bonded only that panel, but that is not time effective and will include huge amounts of money.
So the ways I can look at this:
1- consider the distribution breaker boxes a service all the way to the building and use a bonding jumper at all boxes, then separate the ground grounded bus bar inside the house (will make the series of bonded panels a hazard)
2- consider each of the buildings separate buildings since they are fed from a common breaker box at one point.
3- There are other ways to look at this but they all end the same Bond them and the neutral will be used as a ground fault return path.
My main concern with bonding at each box until the building is that this will bring the panel boxes to the same potential as the neutral and any (even if small) leakage currents/voltages to ground could use a person or anything else present as a parallel path to the source. I also realize that a large (of course a relative term) amount of leakage will trip the breaker due to the low resistance path to the source but if it is not a dead fault or a low resistance (impedance) fault it is possible to have a significant amount of leakage current/voltage on the neutral. breakers that feed the buildings will often be in the range of 60-650 amps so the instantaneous trip of those will be very high, while a lesser fault could cause a potential hazard for hours until the circuit breaker clear the fault.
I feel that an equipment ground wire should be run from the first breaker box after the transformer and bonded only that panel, but that is not time effective and will include huge amounts of money.
So the ways I can look at this:
1- consider the distribution breaker boxes a service all the way to the building and use a bonding jumper at all boxes, then separate the ground grounded bus bar inside the house (will make the series of bonded panels a hazard)
2- consider each of the buildings separate buildings since they are fed from a common breaker box at one point.
3- There are other ways to look at this but they all end the same Bond them and the neutral will be used as a ground fault return path.
My main concern with bonding at each box until the building is that this will bring the panel boxes to the same potential as the neutral and any (even if small) leakage currents/voltages to ground could use a person or anything else present as a parallel path to the source. I also realize that a large (of course a relative term) amount of leakage will trip the breaker due to the low resistance path to the source but if it is not a dead fault or a low resistance (impedance) fault it is possible to have a significant amount of leakage current/voltage on the neutral. breakers that feed the buildings will often be in the range of 60-650 amps so the instantaneous trip of those will be very high, while a lesser fault could cause a potential hazard for hours until the circuit breaker clear the fault.
