National Electrical Installation Standards

Standards as High as Your Own

Thursday, April 4, 2019


Charlie, Please refer to the table. This breaker has AIC ratings for several voltages. We are trying to apply this breaker to a 480 volt high resistance grounded system. This breaker table shows a UL 489 AIC rating at a nominal voltage of 480 volt. So this looks like it can be applied in my system. What I am concerned about is the 600/347 rating listed in the table. Since this is a slash rated breaker and the lower value is less than 480 volt I am not sure this breaker can be applied in the 480 volt HRG system and if used could be a violation of 240.85 and a possible safety hazard. Is this slash rated breaker be used on a 480 volt HRG system?

Thank you.



Hey Jeff thanks for your question. If the circuit breaker has a slash rating that means that it can only be used in a solidly grounded system, not a high impedance system, as stated in 240.85. The voltage to ground cannot exceed the lower voltage rating.

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