Electrician's Licensing Practice Exam

What is not a method for sizing bonding jumpers according to NEC Section 250-28D?

1. Largest ungrounded service conductor

2. Based on the largest phase conductor

3. Equal to the main breaker size

4. Largest sum of service conductors

The correct answer is: Equal to the main breaker size

Sizing bonding jumpers according to the National Electrical Code (NEC) is crucial for ensuring that any ground fault current has a low-impedance path back to the source, which helps in the operation of overcurrent devices to clear the fault. The methods to size bonding jumpers typically include considerations of the largest ungrounded service conductor, the largest phase conductor, and the largest sum of service conductors. The method stating that bonding jumpers should be sized equal to the main breaker size is not a standard practice in the NEC guidelines. The main breaker size is intended for the protection of the overall system and does not necessarily correlate to the requirement for size of the bonding jumpers, which are based on different criteria. Understanding these sizing criteria is crucial for electrical safety and compliance with the NEC, as they help prevent overheating and ensure the proper functioning of the electrical system under fault conditions.