NEC 250.30

[Isaiah]

The design calls for 3, phase conductors and a grounding conductor from the transformer secondary on a delta wye 13.8kV-480V to the switchgear. The XFMR and SWGR both have neutral busses but there is no grounded, ie white (neutral) conductor being routed - only green grounding plus the phases brown, orange and yellow.
Does this design require an additional white, grounded conductor for short circuit purposes even if no line to neutral loads exist?


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[augie47]

If the transformer secondary is not grounded there is no requirement to bring the neutral to the switchgear.*
If it's operating as an ungounded system, ground detectors must be installed per 250.21(B).

*(Provided the gear/breakers are not 480/277 rated)

 

[Isaiah]

If the transformer secondary is not grounded there is no requirement to bring the neutral to the switchgear.*
If it's operating as an ungounded system, ground detectors must be installed per 250.21(B).

*(Provided the gear/breakers are not 480/277 rated)

The one lines show the transformer 2ndary at 480V as being solidly grounded. But there are no 277V loads on the switchgear- strictly 3ph, 3W at 480V, even though the switchgear has a neutral buss.


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[augie47]

If the transformer secondary is solidly grounded then you need a neutral to your gear {250.24(C)}

If's it's service (POCO transformer) then you don't need the EGC as the neutral serves as the ground fault path,.
If's a customer SDS, refer to 250.30. You would need the grounded conductor but the SSBJ would be dependent on Exception 2 to 250.30(A) and exception to 250.30A)(2)
Sounds to me that in your case the 4thr wire from the transformer would be a grounded conductor rather than EGC.

 

[Isaiah]

If the transformer secondary is solidly grounded then you need a neutral to your gear {250.24(C)}

If's it's service (POCO transformer) then you don't need the EGC as the neutral serves as the ground fault path,.
If's a customer SDS, refer to 250.30. You would need the grounded conductor but the SSBJ would be dependent on Exception 2 to 250.30(A) and exception to 250.30A)(2)

Excellent! Thanks Augie


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[don_resqcapt19]

Who owns the transformer?

If this is a customer owned transformer a neutral between the transformer and switchgear is not required, but a supply side bonding jumper would be.

 

[augie47]

Who owns the transformer?

If this is a customer owned transformer a neutral between the transformer and switchgear is not required, but a supply side bonding jumper would be.

Don, what about the "exception" in 250.30(A)(2) ?

 

[Isaiah]

Who owns the transformer?

If this is a customer owned transformer a neutral between the transformer and switchgear is not required, but a supply side bonding jumper would be.

Don and Augie
This is a customer owned transformer. The E&C firm did not specify a neutral so I’m going to go with the SSBJ only philosophy for this installation. Many thanks.


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[don_resqcapt19]

Don, what about the "exception" in 250.30(A)(2) ?

I have never seen that exception applied, but that would permit you to use a grounded conductor without a supply side bonding jumper, and require system bonding jumpers at both the transformer and the panel.

Other than the two points of bonding, the only thing that changes is the color and name of the conductor between the transformer and the panel.