Grounding, Bonding, and Equipment Protection
System vs. Equipment Grounding
Separate these clearly. System grounding connects one conductor of the system to earth (e.g., service neutral). Equipment grounding provides a low-impedance path for fault current back to the source. Bonding connects metal parts to ensure they are at the same potential. Questions often blur these terms-read carefully.
The Grounded Conductor
Know where the neutral may and may not be bonded. At services and at separately derived systems, the neutral is bonded to the enclosure and grounding electrode system; downstream, neutrals and equipment grounding conductors must be kept separate except in specific permitted cases. A subpanel with neutral and ground on the same bus is a classic trap.
Grounding Electrode System
Understand the electrode types, the requirement to use all available electrodes, and the 25-ohm rule with its supplemental electrode provision. Recognize that the grounding electrode conductor is sized from the service conductor table.
Equipment Protection
Overcurrent devices protect conductors, not people. Ground-fault protection of equipment (GFPE) at services above certain thresholds and equipment grounding conductor sizing are frequent topics. Bonding jumpers around concentric knockouts, water piping, and gas piping are common question subjects.
Worked Example
A question describes a subpanel with neutral and ground bonded together. Answer: that is a violation-the neutral must be isolated from the enclosure and the equipment grounding conductor at the subpanel.