In what condition must a main bonding jumper be installed?

A main bonding jumper must be installed as a continuous connection to ensure the electrical grounding system provides a low-impedance path for ground fault currents. This is essential for the safety and effectiveness of the electrical system, as it ensures that any fault conditions will be cleared quickly by the overcurrent protective devices, thereby minimizing the risk of electric shock and fire hazards.

The continuous connection serves to bond all metallic parts together, creating a uniform ground reference which reduces the risk of voltage differences between connected equipment. It effectively ties the grounding system to the grounded neutral conductor, ensuring that the ground fault current will flow back to the source, allowing protective devices to operate correctly.

In contrast, if the jumper were loosely connected or not continuous, there may be additional resistance in the path to ground, which could impede the flow of fault current, potentially resulting in unsafe conditions. Without a solid, continuous connection, the purpose of the main bonding jumper—to provide a reliable path for fault currents—would be compromised.