Journeyman Electrician Exam (NEC)Grounding and BondingMedium
A commercial building utilizes a 277/480-volt, 3-phase, 4-wire service. The main service disconnect enclosure is made of metal. What is the primary purpose of bonding this metal enclosure to the neutral conductor at the service point?
- ATo ensure an effective ground-fault current path.
- BTo provide a low-impedance path for normal operating currents.
- CTo reduce electromagnetic interference (EMI) within the enclosure.
- DTo prevent stray voltage from entering the building's electrical system.
Show answer & explanationAnswer & explanation
Correct answer: A. To ensure an effective ground-fault current path.
The primary purpose of bonding the metal enclosure of the service disconnect to the neutral conductor (which is grounded) at the service point is to establish an effective ground-fault current path. This path facilitates the operation of overcurrent protective devices during a ground-fault condition, ensuring safety by quickly clearing the fault.
Why the other options are wrong
- B. Normal operating currents flow on the phase and neutral conductors, not typically through the enclosure for operation.
- C. EMI reduction is generally handled by shielding and proper wiring practices, not the primary purpose of bonding at the service.
- D. While bonding helps with safety, preventing stray voltage is a secondary effect; the primary goal is fault clearing.
Main Bonding Jumper Purpose
The main bonding jumper connects the equipment grounding conductor(s) and the service equipment enclosure to the grounded conductor at the service, ensuring an effective ground-fault current path.
- Required at the service equipment.
- Connects non-current-carrying metal parts to the grounded conductor.
- Provides a low-impedance path for ground-fault current.
Memory trick: Bonding: Faults find a path, safely!