When can the grounded and grounding conductors share a common bus?

The grounded and grounding conductors can share a common bus only in service panels. This is because service panels are the point where the electrical service enters a building, and they must comply with specific requirements outlined in the National Electrical Code (NEC).

In service panels, the grounded conductor (neutral) and the grounding conductors (equipment grounding) are allowed to be bonded, which means they can share a bus bar. This bonding ensures that in the event of a fault, the grounding system can effectively carry fault current back to the source, enabling proper tripping of overcurrent protection devices.

However, in distribution panels, load-side connections, and various junctions, the grounded and grounding conductors must be kept separate to prevent potential safety hazards, such as shock or overloading, that could occur if the circuit paths for these conductors are mixed. This separation helps maintain the effectiveness of the grounding system and ensures the proper operation of protective devices in the event of faults.