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SCCR with control panels fed in series

Question asked by zeno on Jul 23, 2020
Latest reply on Jul 24, 2020 by chiefns830

I am trying to interpret correctly the logic of the SCCR method suggested in NEC 409.110 (4).b  which is the UL508A SCCR Calculation. According to this method, all the components in the feeder circuit would define the SCCR of a control panel directly. That would mean that the lowest SCCR in the feeder circuit determines the SCCR of the panel. Now, in a particular installation where multiple control panels are powered in series as follows: control panel #1 is the one that receives power from the services and then panel #1 provides power to another control panel #2 and panel #2 then provides power to panel #3. Panel # 2 and # 3 would have installed branch circuit overcurrent protections. Would that mean that elements between the panels like busways, contact conductors, terminals, etc. would belong to the feeder circuit? If that is the case, then the method would create the requirement of high SCCR components between the panels in order to achieve a high SCCR for the panel, even when there are upstream overcurrent protections or current-limiting fuses in the preceding panels which is, as I understand an overkill.

 

By definition, the power circuit ends at the load so as I see it, the feeder circuit would overextend to the downstream panels all the way down to the loads. If that is not the case, then perhaps my logic is flawed and we should dissect the power circuit panel by panel.

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