Ungrounded system

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KasseemF

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A main feeder was pulled from a three phase delta- wye 13.8kV-480V transformer to a building Main distribution panel without a neutral feed. There is a The electrician said it is because the panel is only feeding three phase motors.

Would this installation be considered an ungrounded system according to NEC 250.21?

I have attached a sketch diagram of the installation.
 

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The answer is yes. But is that really the whole question? Aren't you concerned that there may be conditions in your application which REQUIRE it to be grounded; like the type of equipment connected or the need for ground fault indication, and marking?
 
Maybe. Can you clarify where the service disconnect is and if there is neutral running to it? If it is a grounded system and done correctly, the neutral needs to be run to the service disconnect. IF it is meant to be ungrounded, you would want to make sure the utility hasn't grounded the neutral at the transformer secondary.
 
This would seem to depend on the wiring of the secondary of the external transformer.

According to 250.20, if the transformer secondary is wired WYE, then a neutral conductor would be required as the system is a 3 phase, 4 wire WYE system.

If the transformer is wired DELTA without a midpoint grounded phase, then 250.21 would apply and a neutral conductor would not be needed.

Ownership could also matter - in my neck of the woods none of the utilities normally provide ungrounded delta services, therefore regardless of the NEC a neutral conductor is required before you could even get a meter set. If this system is part of a primary metered system, with customer ownership of that external transformer I could see a neutral not being required.
 
Nuber said:
This would seem to depend on the wiring of the secondary of the external transformer.

According to 250.20, if the transformer secondary is wired WYE, then a neutral conductor would be required as the system is a 3 phase, 4 wire WYE system.

If the transformer is wired DELTA without a midpoint grounded phase, then 250.21 would apply and a neutral conductor would not be needed.

Ownership could also matter - in my neck of the woods none of the utilities normally provide ungrounded delta services, therefore regardless of the NEC a neutral conductor is required before you could even get a meter set. If this system is part of a primary metered system, with customer ownership of that external transformer I could see a neutral not being required.
Click to expand...

I dont have my codebook with me, but IIRC correctly the wording is "if the neutral is used as a circuit conductor" then it must be grounded. Thus you could still have a wye transformer and leave it ungrounded. It is worth noting that many/most wye transformers have the wye point bonded to the case. This is why I think it is important to check that the transformer is compatible with an ungrounded system - make sure you are on the same page as the utility and the linemen hooking it up.
 
You could also have a wye service or SDS with the center point grounded and not bring the neutral all the way to utilization equipment.
The neutral must be present at the service disconnect, and probably at the first disconnect of an SDS if it is grounded.

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KasseemF said:
A main feeder was pulled from a three phase delta- wye 13.8kV-480V transformer to a building Main distribution panel without a neutral feed. There is a The electrician said it is because the panel is only feeding three phase motors.

Would this installation be considered an ungrounded system according to NEC 250.21?

I have attached a sketch diagram of the installation.
Click to expand...

I have often come across situations like this where all the load on the service or SDS is only line to line and the installer claims to not need the neutral since he is not connecting line to neutral load. If the service or SDS is grounded at ANY point you don't get to treat as an ungrounded system just because you don't install a neutral or need it. Failure to include a properly sized and installed grounded conductor when supplied by a grounded system indicates a total lack of understanding of the basic tenent of Article 250 and system grounding and bonding. These types of installations can be life threatening.
It should be noted that in this day and age unless there were some special circumstances a truly ungrounded system would be rare or even desired. It would be even more rare to have a service supplied by a POCO that is ungrounded. It would also trigger a number of other code requirements to do so.
Sorry to come across a little harsh, but I also note a number of violations and terminology issues in your diagram.
So I think the first question I would have, is that 13.8/480 transformer a POCO transformer? Whether it is a POCO or privately owned does it have X0 bonded? Even if you determine that it is truly ungrounded, do to the significant negatives and requirements of an ungrounded system you will want to think long and hard about installing an ungrounded system.
 
electrofelon said:
Maybe. Can you clarify where the service disconnect is and if there is neutral running to it? If it is a grounded system and done correctly, the neutral needs to be run to the service disconnect. IF it is meant to be ungrounded, you would want to make sure the utility hasn't grounded the neutral at the transformer secondary.
Click to expand...

This is not a utility transformer. The service disconnect is located at a CEP with neutral coming from the utility company and a breaker in the distribution board feeds this transformer.
 
Since it is not a utility transformer your personnel would have made the decision if the secondary was grounded or un-grounded. If the transformer secondary is ungrounded then no grounded conductor needs to be installed. (Your supply side bonding jumper, #6, is undersized based on 250.30(B) referencing 250.30(A)(2).
250.21(B)would also come into play if its an ungrounded system.
 
It seems to me that if you only pull three conductors from a wye secondary it's still a grounded system if the neutral of the transformer secondary is bonded to ground. The voltages on the phase conductors are still referenced to ground even if a grounded conductor is not present in the wiring. If you short a phase conductor to ground, current will flow back to the source.

Was that the question? Sorry if I missed something.
 
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