in our plant we have a wye connected transformer that supplies our 480V loads, because we have no use for the 277V, we have a 4th wire that is tapped to the grounding of the secondary star-connected and is connected or bonded to the ground busbar of each our plant's panelboards. Is this 4th wire considered a neutral wire or an equipment grounding wire? will there be any code violation if we use a 4-pole automatic transfer switch wherein we connect the said 4th wire on one of the pole to switch the load from our transformer to our generator?
4 pole transfer switch on a 3-phase 3 wire
- Thread starter PT
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stormywyo
Member
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- Stigler, Oklahoma
Up to the first disconnecting means, it is a grounded conductor.From there on it is an equipment grounding conductor. I would look at 250.148 for a code reference. Why would you want to do this anyway??
Pierre C Belarge
Senior Member
- Location
- Westchester County, New York
If this 4th conductor is bonded to the frame of the transformer and X/O at the transformer, it is the grounded (neutral) conductor.
It is not an equipment ground conductor. Therefore it should not be bonded to the grounding bus at secondary panels. If this bus you are speaking of is isolated from the secondary panel enclosures, that is okay.
At that point, it would be permitted to terminate it to the 4th pole of the transfer switch.
If you do not need a grounded (neutral) conductor, why are you going to the expense of the 4-pole transfer switch?
It is not an equipment ground conductor. Therefore it should not be bonded to the grounding bus at secondary panels. If this bus you are speaking of is isolated from the secondary panel enclosures, that is okay.
At that point, it would be permitted to terminate it to the 4th pole of the transfer switch.
If you do not need a grounded (neutral) conductor, why are you going to the expense of the 4-pole transfer switch?
As I wrote before that we are not using any 277V but my boss said first consideration was to conform with NEC Art 250.20B, Art 250.24B & aArt 230.35. He likes to have a separately derived system because our building has many computers and PLCs, so he would like to have our 4th wire conected to the switch. But I have told him that it is the same wire that we used to bond the metal parts of our motors, panels and step-down transformers, thus I believe it is an equipment ground.
Our transfering means is a breaker-type switch, in the event that a line-to-ground fault occurs on the load of the switch it will trip both the normal breaker and not transfer to emergency (because the sensor will detect that there is still power coming from the source) or during maintenance wherein we open both breakers, would that be a hazard because the whole load-side of the switch will not have any connection to ground on these intances? I believe what he wants is applicable only if we have a true nuetral because there would be another wire that will bond all the metal parts of our plant. But as I wrote, we only have a 4th wire that does this.
Our transfering means is a breaker-type switch, in the event that a line-to-ground fault occurs on the load of the switch it will trip both the normal breaker and not transfer to emergency (because the sensor will detect that there is still power coming from the source) or during maintenance wherein we open both breakers, would that be a hazard because the whole load-side of the switch will not have any connection to ground on these intances? I believe what he wants is applicable only if we have a true nuetral because there would be another wire that will bond all the metal parts of our plant. But as I wrote, we only have a 4th wire that does this.
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