Master Electrician Exam (NEC)Grounding and BondingMedium
A master electrician is installing a new 480Y/277V, 3-phase, 4-wire service to a commercial building. The service conductors are 600 kcmil copper. What is the minimum size copper main bonding jumper required for this installation?
- A2/0 AWG
- B4/0 AWG
- C3/0 AWG
- D1/0 AWG
Show answer & explanationAnswer & explanation
Correct answer: A. 2/0 AWG
The main bonding jumper size is determined by the size of the ungrounded service-entrance conductors, as per NEC 250.28(D)(1) and Table 250.102(C)(1). For 600 kcmil copper service conductors, the minimum size copper main bonding jumper is 2/0 AWG.
Why the other options are wrong
- B. Incorrect. This size is significantly larger than required for 600 kcmil copper service conductors.
- C. Incorrect. This size is larger than required for 600 kcmil copper service conductors.
- D. Incorrect. This size is for smaller service conductors.
Main Bonding Jumper Sizing
The main bonding jumper connects the equipment grounding conductor(s) and the service-disconnect enclosure to the grounded conductor of the service, ensuring a low-impedance path for fault current.
- Sized according to NEC 250.28(D)(1) and Table 250.102(C)(1).
- Based on the size of the largest ungrounded service-entrance conductor.
- Must be copper or aluminum/copper-clad aluminum.
Memory trick: Bonding Jumper: Connects the Service to the Grounded Path Safely.