If the largest ungrounded service-entrance conductor is 900 kcmil, what is the minimum size required for a bonding jumper?

The minimum size required for a bonding jumper is determined by the size of the largest ungrounded service-entrance conductor. According to the National Electrical Code (NEC), the bonding jumper must be sized in accordance with Table 250.102(C), which provides the minimum size requirements based on the size of the conductors fed into the system.

For a largest ungrounded service-entrance conductor of 900 kcmil, the bonding jumper must be no smaller than 4/0 copper or 250 kcmil aluminum. Thus, for a conductor size of 900 kcmil, the bonding jumper must be sized at 4/0.

This bond is crucial for ensuring that fault currents have a low-resistance path back to the source, facilitating the operation of overcurrent protection devices in case of faults. A jumper that is sized appropriately is fundamental to establishing safety and compliance with electrical codes. Therefore, the answer of 4/0 is indeed the correct choice based on the NEC standards for bonding jumpers in relation to the service-entrance conductor’s size.