NEC 240.85 CB with Slash rating

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Houston, TX
I currently have a panelboard rated 480/277V, 4W. The panel is equiped with 480/277V slash rated breakers. This panel is feed by a 480V Wye transformer that is high impedance grounded. I do not have a neutral running from the transformer into the equipment. All the breakers are 3phase for 3ph loads. I have a UL inspector who insists this must be a 480, 3W panel per 240.85. This article as I read it, refers to Delta confirgurations where the voltage can exceed the slash rated breaker. I think the inspectors hang up is the article mentions slash rated 480/277V is permitted to be applied in a solidly grounded circuit.

The panel and breakers are slash rated but I am running 3ph, 480V to the panel with no neutral. I don't see how the inspector is confusing this. Do you see any issues with using a slash rated panel and breakers in this application? Since I know this will come up the fault current rating is 65KAIC. I am fine in that respect.


Staff member
State Electrical Inspector (Retired) DINOSAUR
I've only encountered 1 high impedence ground system so I certainly could be mistaken, but until shown otherwise I would not consider that a "solidly grounded system" and would not accept slash rated breakers.

mcclary's electrical

Senior Member
IMO,,,since the nominal voltage from any phase to ground does not exceed the lower of the two values of the slash rated breaker,,,,and since the nominal voltage of any two phases does not exceed the higher of the two values,,,,,it should pass.
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