2-kVA Transformer ground, Does 250.30 apply?

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dddknowles

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I have 480-volt, 3-phase, 50-amp circuit breaker that supplies a 30-amp fused safety switch for a steam boiler and in parallel another 10-amp fused safety switch. The 10-amp fused safety switch feeds a 2-kVA, 1-phase, 480-to-120-volt transformer. The secondary of the transformers feeds a 20-amp fused safety switch that provides power to two small 120-volt loads related to the boiler. I have not treated the 2-kVA transformer as a separately derived system. I have extended the equipment ground from 50-amp 480-volt circuit breaker to the 10-amp fused safety switch, from the safety switch to one side of the transformer secondary, and also to all associated enclosures. I am running a current carrying neutral from the secoudary of the 120-volt transformer and also a non-current carrying ground. Both the neutral and non-current carrying grounds are extended to the 120-volt loads.

Is this arrangement in compliance NEC 2005?
 
What is the location of the system bonding jumper
What is your grounding electrode (system) and where does it connect to?
 
Response to Tom's questions.

Response to Tom's questions.

System bonding jumper is at an upstream 480-volt service entrance panel. The grounding electrode conductor is also there.
 
System bonding jumper is at an upstream 480-volt service entrance panel. The grounding electrode conductor is also there.
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No...these items have to be on the secondary side of the SDS.
Don
 
Response to questions and SDS comments

Response to questions and SDS comments

The transformer and disconnects will be field installed and are not part of a manufacturer's system.

I want to thank all who commented. I appreciate your help. Respectfully I still have some questions. Some comments are based on this 2-kVA step-down transformer being required to be a separately derived system. Is it a NEC code violation to install a 2-kVA step-down transformer without treating it as a separately derived system? The transformer in this case has a secondary full load of 16.7-amps. The equipment ground from the primary has a 20-amp rating. Is a #8 AWG copper GEC as required for a SDS by 250.30 the only choice?
 
I don't see any exceptions that would apply to your 2kVA transformer or to the #8 minimum size for the GEC.
Don
 
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