Journeyman Electrician Exam (NEC)Grounding and BondingMedium
A journeyman is installing a new 400-ampere, 480Y/277-volt, 3-phase, 4-wire service. The service-entrance conductors are 500 kcmil copper. What is the minimum size for the main bonding jumper?
- A2/0 AWG copper
- B3/0 AWG copper
- C1/0 AWG copper
- D2 AWG copper
Show answer & explanationAnswer & explanation
Correct answer: B. 3/0 AWG copper
According to NEC 250.102(C)(1) and Table 250.102(C)(1), for service-entrance conductors of 500 kcmil copper, the minimum size for the main bonding jumper is 3/0 AWG copper.
Why the other options are wrong
- A. This size is too small for a 400-ampere service with 500 kcmil copper conductors.
- C. This size is too small for a 400-ampere service with 500 kcmil copper conductors.
- D. This size is too small for a 400-ampere service with 500 kcmil copper conductors.
Main Bonding Jumper Sizing
The main bonding jumper connects the equipment grounding conductor(s) and the service equipment enclosure to the grounded conductor at the service and is sized according to NEC 250.102(C)(1) based on the service-entrance conductor size.
- Sized from NEC Table 250.102(C)(1).
- Based on the largest ungrounded service-entrance conductor.
- Ensures an effective ground-fault current path.
Memory trick: Bonding Jumper: Service conductor's friend!