Transformer GEC & panel OCP

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wirebender

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I have an 800A fused 277/480 wye service entrance disconnect on the outside of a metal building feeding 2-400 panels immediately inside and directly behind the disco.

One panel feeds a 75kva 480/208 transformer sitting right next to it, with the 208 panel right next to the transformer on the other side.

The building steel does not qualify as an electrode, it is basically just the metal frame of the building.

No metal water piping.

Can I run the GEC for the transformer from the bonding point in the outside disconnect through the indoor panel with the feeders and then through the FMC with the supply conductors to the transformer?

Also, while researching this in the archives, I have come to the conclusion that the 225A, 208 wye panel will have to have a main breaker even though, IMO, it is protected by the 100 amp breaker feeding the transformer. Is this correct?

And do the 2-400A panels require main breakers?

It's past my bedtime, so I will check back tomorrow to answer any questions.
Thanks.
 
Can I run the GEC for the transformer from the bonding point in the outside disconnect through the indoor panel with the feeders and then through the FMC with the supply conductors to the transformer?

No, the GEC can't run to the bonding point in the main disconnect. Per 250.30(A)(3), the GEC shall connect to a grounding electrode.

Also, while researching this in the archives, I have come to the conclusion that the 225A, 208 wye panel will have to have a main breaker even though, IMO, it is protected by the 100 amp breaker feeding the transformer. Is this correct?

Yes the 208V panel will need a main breaker (or a breaker on the secondary side before the panel) per 408.36(B). See also 240.21(C) for protection of the secondary conductors.

And do the 2-400A panels require main breakers?

Yes, per 408.36 the 400A panels will require main breakers (or additional breakers installed before the panels.) See also 240.21(B) if the feeder to each panel is a tap from the 800A disconnect.
 
Can I run the GEC for the transformer from the bonding point in the outside disconnect through the indoor panel with the feeders and then through the FMC with the supply conductors to the transformer?

The GEC has to be install in one continuous length to the electrode(250.64C). Going to the outdoor disconnect will not be sat.

wirebender said:
Also, while researching this in the archives, I have come to the conclusion that the 225A, 208 wye panel will have to have a main breaker even though, IMO, it is protected by the 100 amp breaker feeding the transformer. Is this correct?

And do the 2-400A panels require main breakers?

Thanks.
The 100 amp breaker is protecting the transformer (450.3B).The 225 amp breaker is required for transformer conductor protection, and panel board protection. See 240.21c1 and 408.36, . The 400 amp breakers are required in the panels as well as full sized conductors rated for 400 amps.See 408.36 and 240.21B

Rick
 
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