Step Down Transformer

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Ed Kelley

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Recently I had a Inspector classify a 5Kv transformer as a "Separately Derived System" Was on a 480V Y systerm step down to 240/120V Single phase. to power a 6cir panel for a battrey charger and a area light and 1 GFCI. He had me run a # 6 ground Back to the main system Ground rod , Making a Parallel ground. and MAde me run the Secondary in # 6 THHN to the panel.
 
The inspector was correct in his calling that a SDS.
Since you were powering 120 devices, you obviously needed a neutral.
A SDS must have a GEC to an electrode as defined in 250.30. You would need to review 250.30(A)(7) to see if the rod was the appropriate GE.
 
augie47 said:
The inspector was correct in his calling that a SDS.
Since you were powering 120 devices, you obviously needed a neutral.
A SDS must have a GEC to an electrode as defined in 250.30. You would need to review 250.30(A)(7) to see if the rod was the appropriate GE.
Click to expand...

If he doesn't use a 120volt loads it make a diferent in
the classification of SDS?
 
It would still be a SDS by definition.
Separately Derived System. A premises wiring system whose power is derived from a source of electric energy or equipment other than a service. Such systems have no direct electrical connection, including a solidly connected grounded circuit conductor, to supply conductors originating in another system.
and
250.20(B) would require the neutral bond whether used or not, IMHO

(B) Alternating-Current Systems of 50 Volts to 1000 Volts. Alternating-current systems of 50 volts to 1000 volts that supply premises wiring and premises wiring systems shall be grounded under any of the following conditions:
(1) Where the system can be grounded so that the maximum voltage to ground on the ungrounded conductors does not exceed 150 volts ...............................
 
augie47 said:
It would still be a SDS by definition.
Separately Derived System. A premises wiring system whose power is derived from a source of electric energy or equipment other than a service. Such systems have no direct electrical connection, including a solidly connected grounded circuit conductor, to supply conductors originating in another system.
and
250.20(B) would require the neutral bond whether used or not, IMHO

(B) Alternating-Current Systems of 50 Volts to 1000 Volts. Alternating-current systems of 50 volts to 1000 volts that supply premises wiring and premises wiring systems shall be grounded under any of the following conditions:
(1) Where the system can be grounded so that the maximum voltage to ground on the ungrounded conductors does not exceed 150 volts ...............................
Click to expand...

I agree with Gus.:)

Chris
 
Ed, welcome to the forum! :)

In a nutshell, the secondary of a transformer is the origination of a new suppply source, so it needs a grounding electrode system, as well as having the new neutral bonded to that system.
 
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