Modelling Multi-Section Switchboard in ETAP

I am working on an arc flash study for a system with a multi-section main switchboard. I have created the model in ETAP. I modeled each of the three sections as a separate busses linked in order by very low-value Impedances (since you can't link a bus to a bus directly in ETAP; I've also modeled it with an appropriately sized conductor of negligible distance). Each section is a separate compartment, with the first section with the main breaker from the utility being different dimensions than the other two sections.

The arc flash analysis in ETAP can't determine a FCT for the first section with the utility main breaker. I'm guessing this has something to do with not being able to isolate from the back-current coming to the bus from the second section of the MSB. However, it seems like that problem should apply to the other two busses for the MSB as well, but ETAP did find a FCT for both of those.

Is there a better way to model a multi-section main switchboard? Is there a workaround for this issue if anyone else has encountered it?
 

jim dungar

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Is there a better way to model a multi-section main switchboard? Is there a workaround for this issue if anyone else has encountered it?
Yes. As a single bus location, unless you know that there are interior barriers that are specifically rated to contain or slow down the propagation of an arcing event and its by products.

Relatively very little 600V equipment is built with internal compartments, while it is pretty common for medium voltage. The problem is if the barriers are rated for arc flash mitigation.
 
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