Journeyman Electrician Exam (NEC)Grounding and BondingMedium
A commercial building has a 120/208-volt, 3-phase, 4-wire service. The main bonding jumper is made of copper. If the ungrounded service-entrance conductors are 350 kcmil copper, what is the minimum size copper main bonding jumper required, according to NEC® Table 250.102(C)(1)?
- A2/0 AWG
- B1/0 AWG
- CNo. 1 AWG
- DNo. 2 AWG
Show answer & explanationAnswer & explanation
Correct answer: A. 2/0 AWG
According to NEC® Table 250.102(C)(1), for ungrounded service-entrance conductors with a size of 350 kcmil copper, the minimum size copper main bonding jumper required is 2/0 AWG.
Why the other options are wrong
- B. 1/0 AWG is for service conductors up to 4/0 AWG.
- C. No. 1 AWG is for service conductors up to 3/0 AWG.
- D. No. 2 AWG is for service conductors up to 2/0 AWG.
Main Bonding Jumper Sizing
The main bonding jumper (MBJ) size is determined by the size of the largest ungrounded service-entrance conductors, as per NEC® Table 250.102(C)(1).
- Connects the equipment grounding conductor to the grounded service conductor and service enclosure.
- Sized based on ungrounded service-entrance conductors.
- Refer to NEC® Table 250.102(C)(1).
Memory trick: MBJ links to the service's biggest wire, like a big brother.