With respect to Art. 240 (Overcurrent Protection), which of the following scenarios permits the use of a slash rated circuit breaker in a circuit?

  1. Corner grounded 480V, 3-phase system
  2. Resistance grounded 480/277V, 3-phase system
  3. Ungrounded 480V, 3-phase system
  4. Solidly grounded 480/277V, 3-phase system
  5. None of the above

Answer: D

As noted in the first sentence of the first paragraph of 240.85, "A circuit breaker with a straight voltage rating, such as 240V or 480V, shall be permitted to be applied in a circuit in which the nominal voltage between any two conductors does not exceed the circuits breaker's voltage rating."

As noted in the first sentence of the second paragraph of 240.85, "A circuit breaker with a slash rating, such as 120/240V or 480Y/277V, shall be permitted to be applied in a solidly grounded circuit where the nominal voltage of any conductor to ground does not exceed the lower of the two values of the circuit breaker’s voltage rating, and the nominal voltage between any two conductors does not exceed the higher value of the circuit breaker's voltage rating."

Owen is the owner and president of National Code Seminars and the holder of master electrician certifications in 46 states. He can be reached at necexpert@aol.com.