When sizing the system bonding jumper, which rule is used if it is based on the size of the largest ungrounded phase conductor?

The correct answer is based on the sizing of the system bonding jumper as it relates to the size of the largest ungrounded phase conductor. The 12.5% rule is a standard in electrical bonding practices that dictates the sizing parameters for bonding jumpers to ensure proper safety and functionality in electrical installations.

This rule ensures that the bonding jumper is adequately sized to handle potential fault currents without risking failure or creating hazardous conditions. By using 12.5% of the largest ungrounded phase conductor, it establishes a balance between providing a robust connection that can effectively minimize the risk of electrical shock or fire while not being overly excessive, which could result in additional unnecessary costs or complications.

The bonding jumper serves to connect conductive parts and create an effective ground to stabilize the electrical system, ultimately ensuring that if there were a fault, the electrical current would have a safe path and mitigate risk to personnel and equipment.