Master Electrician Exam (NEC)Services, Feeders, and Branch CircuitsEasy
A master electrician is installing a new 200A, 120/240V single-phase service for a dwelling unit. The service entrance conductors are 3/0 AWG copper. What is the minimum size required for the main bonding jumper if it is a wire type?
- A1/0 AWG copper
- B2 AWG copper
- C6 AWG copper
- D4 AWG copper
Show answer & explanationAnswer & explanation
Correct answer: B. 2 AWG copper
NEC Table 250.102(C)(1) specifies the size of the supply-side bonding jumper or main bonding jumper based on the largest ungrounded service-entrance conductor. For 3/0 AWG copper service conductors, the minimum size for the main bonding jumper is 2 AWG copper.
Why the other options are wrong
- A. This size is larger than required by NEC Table 250.102(C)(1), but not the minimum.
- C. This size is too small according to NEC Table 250.102(C)(1).
- D. This size is too small according to NEC Table 250.102(C)(1).
Main Bonding Jumper Sizing (Wire Type)
The main bonding jumper (MBJ) is a conductor that connects the equipment grounding conductor(s) and the service-disconnect enclosure to the grounded conductor of the service.
- Sized based on the largest ungrounded service-entrance conductor.
- Refer to NEC Table 250.102(C)(1) for sizing.
- Ensures a low-impedance path for ground-fault current.
Memory trick: Bonding bridges the gap for safety.