Coordination and arc flash

[Isaiah]

We have 480V 3ph 3w power Panelboards with an 800A rating. Some of these panels have been replaced with 3 phase Enclosures (with copper bus bars) and disconnect switches, using the ten foot tap rule . The Panelboards were part of the initial coordination study and Arc Flash labels were produced for each one, however now that they’ve been replaced I’m wondering if the same criteria and approach distances still apply?


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[HarrySlother]

From a CYA perspective, no. The calculations need to be re-done for the disconnects because the taps could limit the fault current below what was available at the panel. This could cut below the instantaneous setting of the 800A feeder breaker and lead to a longer arc flash. Realistically, with taps less than 10' I doubt it will effect the calculations much, but it's the one scenario out of a hundred that you need to account for.

This is all assuming you need stickers on these disconnects. If they're non-fused and you can safely shut off the feeder breaker then you may never need to work on them live. See 110.16 (A)

 

[D. Castor]

You need to update the arc-flash labels to reflect the updated system.