Transfer Switch - Protecting Conductors at Point of Supply

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xguard

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Baton Rouge, LA
We have a 480 Volt 3 phase generator with a 225 A breaker. From there we go to an automatic transfer switch with 4/0 conductors. From the transfer switch we have 2/0 conductors to a panel inside a building where they land in a distribution panel with a 175 A main breaker. The service conductors to the transfer switch from the utility are 2/0.

I don't believe the 2/0 conductors from the transfer switch to the panel inside the building are adequately protected when we are on generator power.

The run is greater than 25 feet, it also does not run take the most direct route to the panel. I'm being told the 2/0 conductors are protected by the 175A Main breaker in the dirstribution panel, I don't agree with this as they don't fall under tap rules, or service entrance conductors rules. The transfer switch is service entrance rated.

What am I missing?
 
xguard said:
We have a 480 Volt 3 phase generator with a 225 A breaker. From there we go to an automatic transfer switch with 4/0 conductors. From the transfer switch we have 2/0 conductors to a panel inside a building where they land in a distribution panel with a 175 A main breaker. The service conductors to the transfer switch from the utility are 2/0.

I don't believe the 2/0 conductors from the transfer switch to the panel inside the building are adequately protected when we are on generator power.

The run is greater than 25 feet, it also does not run take the most direct route to the panel. I'm being told the 2/0 conductors are protected by the 175A Main breaker in the dirstribution panel, I don't agree with this as they don't fall under tap rules, or service entrance conductors rules. The transfer switch is service entrance rated.

What am I missing?
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Is the 175A c/b (in the panel) immediately inside the building where the conductors enter, or do the conductors run for a length inside the building before they reach the panel?

If the panel is immediately inside the building, then you might meet the 240.21(B)(5) - Outside Tap Conductors of Unlimited Length.
 
david luchini said:
Is the 175A c/b (in the panel) immediately inside the building where the conductors enter, or do the conductors run for a length inside the building before they reach the panel?

If the panel is immediately inside the building, then you might meet the 240.21(B)(5) - Outside Tap Conductors of Unlimited Length.
Click to expand...

The panel is immediately inside the building. The panel though is not "nearest the point of entrance of the conductors", I believe the conductors were routed the scenic route to the panel.
 
I don't think this will satisfy the tap rules, if the conductors run any significant distance inside the building before reaching the panel. You have several options. The simplest would be to replace the generator breaker with a 175 amp breaker. It seems that that is all the power that the building needs anyway. Another option, not as simple, is to interrupt the conduit close to where the conductors enter the building, either inside or outside, and put an enclosed circuit breaker or fused disconnect at that location. It would have to be service-rated, and you would need to run an EGC from there to the panel, as well as removing the N-G bond at the panel.
 
charlie b said:
I don't think this will satisfy the tap rules, if the conductors run any significant distance inside the building before reaching the panel. You have several options. The simplest would be to replace the generator breaker with a 175 amp breaker. It seems that that is all the power that the building needs anyway.
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I agree. With the conductors running through the building before reaching the panel, the tap rules can't be satisfied.
charlie b said:
Another option, not as simple, is to interrupt the conduit close to where the conductors enter the building, either inside or outside, and put an enclosed circuit breaker or fused disconnect at that location. It would have to be service-rated, and you would need to run an EGC from there to the panel, as well as removing the N-G bond at the panel.
Click to expand...

This option would work, but the switch needn't be service-rated, as the ATS is.
 
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