NEC Article 250.30 (A) (1) exception 2

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coynetoss

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In Article 250.30 (A) (1) exception 2, could someone clarify this content.
On recent drawings we are now seeing a Grounding or Bonding conductor contained within parallel secondaries from a utility transformer to a switchboard.
Always have understood that secondaries deriving from a separately derived system did not contain a ground or bonding conductor. The grounding electric conductor was derived at the 1st Over current device at the Service entrance.
Has there been a change, that many are not aware of, and also the content of the exception is confusing.
Any answers or comments
Thanks Coynetoss
 
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Not sure if Im reading your question wrong. 250.30 applies to grounding separately derived systems but your question refers to a Utility Transformer. That would make the conductors service entrance conductors not transformer secondary conductors and 250.24 would apply. Again, not sure if Im reading the question correctly.

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It is confusing. Let's talk about a separately derived system downstream of the utility service.

There is the wire that connects the ground bar and the neutral bar. I prefer to do this at the distribution panel or switchboard immediately downstream of the transformer. This wire is the Main Bonding Jumper. Then there is the wire that runs from the neutral bar to planet earth. That is the Grounding Electrode Conductor. Then there are wires that run from the grounding bar to the external metal parts of downstream loads. These are Equipment Grounding Conductors. Finally, there is the wire that runs from (as I understand it) the neutral center point of the transformer to the neutral bar at the switchboard. That is the Supply Side Bonding Jumper. That is the wire you are seeing in the raceway(s) leaving the transformer. It is discussed in 250.102.
 
coynetoss said:
In Article 250.30 (A) (1) exception 2, could someone clarify this content.
On recent drawings we are now seeing a Grounding or Bonding conductor contained within parallel secondaries from a utility transformer to a switchboard.
Always have understood that secondaries deriving from a separately derived system did not contain a ground or bonding conductor. The grounding electric conductor was derived at the 1st Over current device at the Service entrance.
Has there been a change, that many are not aware of, and also the content of the exception is confusing.
Any answers or comments
Thanks Coynetoss
Click to expand...
I agree with richie921, you are describing a service, not a SDS.

Roger
 
Clarification

Clarification

Follow Up

A 3phase 4wire 277/480v systems, supply side conductors run in 4 paralleled PVC's, below ground, eminating from a Grounded Pad Mount 750KVA transformer to an interior enclosure 1200A SWB . Secondary connections are X1,X2,X3 and X0orN to L1,L2,L3,N
The Pad mount is 2 point grounded with 2/0 ground and ground rods
Question:
Do the PVC raceways require a separate ground(Bond) conductor to be contained within the raceways with the 4 conductors in each of the paralleled secondaries.
Or is this NOT necessary and the EGC system ground begins at the 1st service disconnecting means at the switchboard.
 
coynetoss said:
Follow Up

A 3phase 4wire 277/480v systems, supply side conductors run in 4 paralleled PVC's, below ground, eminating from a Grounded Pad Mount 750KVA transformer to an interior enclosure 1200A SWB . Secondary connections are X1,X2,X3 and X0orN to L1,L2,L3,N
The Pad mount is 2 point grounded with 2/0 ground and ground rods
Question:
Do the PVC raceways require a separate ground(Bond) conductor to be contained within the raceways with the 4 conductors in each of the paralleled secondaries.
Or is this NOT necessary and the EGC system ground begins at the 1st service disconnecting means at the switchboard.
Click to expand...

In the situation you are describing with a POCO transformer it would be a violation to install a grounding conductor (in this case it would be termed a supply side bonding jumper). The reason is that a POCO that is supplying a grounded 480Y277 service will always have the X0 terminal of transformer bonded the the transformer case, GES and primary neutral. If you then were to run a supply side bonding jumper it would be in parallel with the grounded service conductor and create another code issue.
I might add that I have also seen this on drawings a number of times the way you describe. I always just assumed that it was carelessness on the part of the person who drafted it. I've even seen cases where the electrician just blindly installs as shown on the drawing and the POCO folks (if they are well informed) will just cut them off and abandon them. To connect them can lead to problems.
 
coynetoss said:
the EGC system ground begins at the 1st service disconnecting means at the switchboard.
Click to expand...
Dave already said it but I will reiterate, your statement is correct.

Texie also points out that you would be creating a parallel "neutral"

Roger
 
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