What is the minimum percentage requirement for a main bonding jumper according to NEC?

• A. 5%
• B. 10%
• C. 12.5%
• D. 20%

Answer: (C)

The minimum percentage requirement for a main bonding jumper according to the National Electrical Code (NEC) is based on the size of the service conductors. Specifically, the NEC stipulates that the bonding jumper must be sized according to a specific formula, which includes a minimum of 12.5% of the total ungrounded service conductors' rating.

This percentage signifies the necessary capacity of the main bonding jumper to ensure safe and effective grounding. A proper bonding jumper helps to reduce the risk of electrical shock and provides a clear path for fault currents. By using this percentage as a guideline, electricians ensure compliance with safety standards while promoting effective electrical system operation.

The other options do not meet the NEC's requirements, as they either under-specify or over-specify the necessary capacity for a main bonding jumper.