Master Electrician Exam (NEC)Grounding and BondingHard
A master electrician is installing a new 480V, 3-phase, 4-wire wye system for a commercial kitchen. The main service will be located in a dedicated electrical room. What is the minimum size copper main bonding jumper required if the ungrounded service-entrance conductors are 700 kcmil copper?
- ANo. 2/0 AWG
- BNo. 1/0 AWG
- CNo. 3/0 AWG
- DNo. 4/0 AWG
Show answer & explanationAnswer & explanation
Correct answer: A. No. 2/0 AWG
According to NEC 250.28(D)(1) and Table 250.102(C)(1), the main bonding jumper shall not be smaller than the sizes shown in Table 250.102(C)(1). For ungrounded service-entrance conductors of 700 kcmil copper, the minimum size copper main bonding jumper required is No. 2/0 AWG.
Why the other options are wrong
- B. No. 1/0 AWG is for service conductors up to 400 kcmil copper.
- C. No. 3/0 AWG is for service conductors up to 800 kcmil copper.
- D. No. 4/0 AWG is for service conductors up to 1100 kcmil copper.
Main Bonding Jumper Sizing
The main bonding jumper size is determined by the size of the largest ungrounded service-entrance conductor or equivalent area for parallel conductors, referenced in NEC Table 250.102(C)(1).
- Sized based on the largest ungrounded service conductor.
- Found in NEC 250.28(D) and Table 250.102(C)(1).
- Ensures a low-impedance path for fault current at the service.
Memory trick: Bonding jumper size: service conductors tell the tale.