Floating Neutral on service entrance wye xformer

[jenglhardt]

The utility recently replaced a failing delta|delta 1000kva service entrance transformer in a commercial office building. The secondary is connected as a 3W+G system. There is no N-G bond and no ground fault detection.

250.20 Requires N-G bond where the system is 3-phase, 4-wire, wye connected in which the neutral conductor is used as a circuit conductor, however, the neutral is not used.

Since this is a wye secondary service entrance, wouldn't article 250.30 "Grounding Separately Derived Alternating-Current Systems" require a N-G bond?

Please help...we are concerned that this is a serious safety issue.

 

[augie47]

Delta supply to a commercial office building ????

 

[Rockyd]

Since this is a wye secondary service entrance, wouldn't article 250.30 "Grounding Separately Derived Alternating-Current Systems" require a N-G bond?

If you are saying that your secondary transformer is a Delta/Wye set up, and there is no N-G bond, would suspect you have a floating nuetral voltage of unknown proportions in your building.

Not seeing this as a healthy/safe set up for many reasons.

Is this the case?

 

[Cold Fusion]

The utility recently replaced a failing delta|delta 1000kva service entrance transformer in a commercial office building. The secondary is connected as a 3W+G system. There is no N-G bond and no ground fault detection.

Since this is a wye secondary service entrance, wouldn't article 250.30 "Grounding Separately Derived Alternating-Current Systems" require a N-G bond?.

j -
You got me confused. Are you saying they replaced a Delta primary/ungrounded Delta secondary transformer with a Delta primary/ungrounded Wye secondary?

If that is what you were meaning to say - you are no worse off than you were with the delta/delta.

What you are describing is definitely a poor design and has some code issues. A POCO supplied ungrounded delta - that is an oddity. It would only be the second one I have heard of.

Just curious:
What was the secondary voltage before the change out?
What is the secondary voltage now?

cf

 

[SomeNewGuy]

Of course utilities are exempted from the NEC. Why not bond at the panelboard or switch-gear, or consult AHJ for sure?

 

[Smart $]

The utility recently replaced a failing delta|delta 1000kva service entrance transformer in a commercial office building. The secondary is connected as a 3W+G system. There is no N-G bond and no ground fault detection.

250.20 Requires N-G bond where the system is 3-phase, 4-wire, wye connected in which the neutral conductor is used as a circuit conductor, however, the neutral is not used.

Since this is a wye secondary service entrance, wouldn't article 250.30 "Grounding Separately Derived Alternating-Current Systems" require a N-G bond?

Please help...we are concerned that this is a serious safety issue.

What was your service before the change out?

It doesn't matter how the poco configures there primary or secondary. The only issue here is what you had before vs now, as in voltage, how many wires, and which is grounded or the presence of ground-fault detection.

When you say there is no N-G bond, are you talking at the service disconnect or at the transformer... or both?

 

[charlie]

On this issue, we adhere to the same rules that you do. There is nothing wrong with replacing a 480 volt delta ungrounded service that had no ground detectors with a 480 volt wye ungrounded service where the neutral is not taken out. Everything is as it was.

I am, however, confused with your comments about the grounding. We do not permit any customer grounding to be connected to our grounding system except through the neutral which is not used in this case. :-?

 

[LarryFine]

The utility recently replaced a failing delta|delta 1000kva service entrance transformer in a commercial office building. The secondary is connected as a 3W+G system. There is no N-G bond and no ground fault detection.

It sounds like there never was a neutral from this description. What bond are you saying is/was missing?