Grounding, Bonding, and Ground-Fault Protection
Grounding, Bonding, and Ground-Fault Protection tests the low-impedance path that carries fault current and the system that detects ground faults. The exam distinguishes grounding electrodes, equipment grounding conductors, bonding jumpers, and ground-fault protection.
Core rules
- Bonding connects metal parts to create an equipotential path; grounding connects the system to earth. Both matter, but bonding is critical for fault clearing.
- Verify equipment grounding conductor continuity with a low-resistance ohmmeter, not a standard continuity beeper alone.
- Measure grounding electrode resistance with fall-of-potential or induced-frequency methods. The potential probe is placed at about 62% of the current-electrode spacing for a simple fall-of-potential test.
- Clamp-on ground testers are valid only on multi-grounded systems with a return path; they are not a universal earth-resistance tester.
- Ground-fault protection must be tested for pickup, timing, and coordination with upstream devices.
Worked example
A fall-of-potential test uses a 100 ft current-electrode spacing. The potential probe is placed near 62 ft and moved slightly to check the plateau. The measured resistance is 4.8 Ω against a 5 Ω specification. The technician records the reading but notes it is close to the limit, checks soil conditions and connections, and compares with prior data. The reasoning is that a marginal pass is not the same as a stable pass.
Traps
Using a clamp-on tester on a single ground rod; relying on a continuity beeper for a bonding conductor; testing ground resistance without disconnecting parallel paths when required; and ignoring seasonal soil moisture.