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Question 1
What is the NEC definition of 'overcurrent'?
Answer: Any current in excess of the rated current of equipment or the ampacity of a conductor. It may result from overload, short circuit, or ground fault.
Question 2
What is the difference between an overload and a short circuit?
Answer: An overload is excess current flowing in a normal path (e.g., too many loads), while a short circuit is an abnormally low-resistance connection between conductors that causes very high fault current.
Question 3
What does the term 'ampacity' mean as it relates to overcurrent protection?
Answer: Ampacity is the maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating.
Question 4
What is an 'inverse time' circuit breaker?
Answer: A circuit breaker that has an intentional delay in its tripping time that decreases as the magnitude of the overcurrent increases — higher fault currents trip it faster.
Question 5
What is the purpose of an overcurrent protective device (OCPD)?
Answer: To open the circuit automatically when current exceeds the device's rating, protecting conductors and equipment from damage due to heat or fault current.