A master electrician is installing a new 400A, 480Y/277V, 3-phase, 4-wire service. The service entrance conductors are 600 kcmil copper, installed in parallel in two raceways. What is the minimum size required for the main bonding jumper if it is a wire type?
- A1/0 AWG copper
- B2/0 AWG copper
- C3/0 AWG copper
- D250 kcmil copper
Show answer & explanationAnswer & explanation
Correct answer: B. 2/0 AWG copper
According to NEC 250.102(C)(1), when the ungrounded service entrance conductors are paralleled, the main bonding jumper is sized based on the equivalent area of the largest ungrounded service-entrance conductor. Two 600 kcmil conductors in parallel have an equivalent area of 1200 kcmil. Referring to Table 250.102(C)(1), for service conductors over 1100 kcmil copper, the minimum size for the main bonding jumper is 2/0 AWG copper. Note: The table value for 1100 kcmil and above is 2/0 AWG copper.
Why the other options are wrong
- A. This size is too small for the equivalent area of the service conductors.
- C. This size is larger than the minimum required.
- D. This size is larger than the minimum required.
Main Bonding Jumper Sizing (Parallel Conductors)
When service conductors are installed in parallel, the main bonding jumper must be sized based on the equivalent cross-sectional area of the largest ungrounded service conductor or set of conductors.
- Sum the kcmil of all parallel ungrounded service conductors.
- Use NEC Table 250.102(C)(1) with this equivalent area.
- The table provides the minimum size for copper or aluminum bonding jumpers.
Memory trick: Parallel conductors mean sum the kcmil for bonding.