How is the size of a main bonding jumper typically derived according to the NEC®?

The size of a main bonding jumper is typically derived based on the rating of the overcurrent protection device, such as circuit breakers, used in the electrical system. This practice is rooted in the NEC® (National Electrical Code) guidelines, which dictate that the bonding jumper must be able to safely carry the maximum fault current that could occur in the system without allowing dangerous voltages to appear on equipment enclosures or conducting parts.

When the rating of the circuit breakers is established, it indicates the level of protection against overcurrent situations, and consequently, the main bonding jumper must be appropriately sized in relation to that rating to ensure effective grounding and bonding. This connection plays a crucial role in maintaining safety within the electrical installation, allowing a path for fault currents to help facilitate the operation of protective devices.

Other considerations related to conductor size, the number of devices, or load evaluations do not directly influence the sizing of the main bonding jumper as fundamentally as the overcurrent protection ratings provide. In a properly designed system, the bonding jumper’s size is directly tied to ensuring that it can withstand potential fault conditions, which is primarily dictated by the circuit breaker rating.