National Electrical Installation Standards

Standards as High as Your Own

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Thursday, April 4, 2019

Question:

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.

Jeff
A

Answer:

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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