Grounding and bonding fundamentals

State the distinct jobs of grounding and bonding and identify the fault-current return path in a system.

Grounding and bonding are two different jobs that share hardware. Grounding connects the system or equipment to earth, which stabilises voltage to ground and gives lightning and surges a reference. Bonding connects conductive parts together so they stay at the same potential and so fault current has a low-impedance path back to the source.

The critical insight is that the earth is not the fault-current return path. Overcurrent devices open because fault current returns to the source through the equipment grounding conductor and the bonded metallic path, not through soil. Soil resistance is far too high to carry enough current to trip a breaker.

Distinguish the conductors by job: the grounded (neutral) conductor carries normal unbalanced current; the equipment grounding conductor carries fault current only; the grounding electrode conductor references the system to earth. Connecting them at more than one point creates objectionable current on metal parts.

Predicting before you experiment is what makes the result stick. There is no penalty for being wrong here.

Trace a ground fault and see what happens when the bonding path is broken.

1. Set up a normal service with the neutral-to-ground bond at the service only.
2. Apply a line-to-enclosure fault and follow the return path back to the source.
3. Remove or degrade the equipment grounding conductor and repeat.
4. Note what happens to fault current magnitude and to touch potential on the enclosure.

Describe a situation where equipment is 'grounded' but not effectively bonded, and explain the hazard that remains.