Grounding and bonding

Grounding and bonding are two different jobs that share a wire color. GROUNDING connects the system to earth, stabilizing voltage relative to ground and dissipating lightning and line surges. BONDING connects all metal parts together so they sit at the same potential and provide a low-impedance fault path back to the source. The dirt does almost nothing for fault clearing — bonding does the work.

This is the single most misunderstood idea in residential wiring. When a hot conductor touches a metal enclosure, what trips the breaker is not electricity flowing into the earth; it is the bonded metallic path carrying a huge fault current back to the source, exceeding the breaker's magnetic trip in milliseconds. A ground rod alone has far too much resistance to ever trip a breaker.

The critical rule: the grounded (neutral) and grounding conductors are bonded at exactly ONE point — the service disconnect via the main bonding jumper. Downstream of that, they must stay separate. Bonding them again in a subpanel puts normal return current onto the equipment ground and every bonded metal surface in the building — a live hazard that looks perfectly fine until someone touches something.

Exam focus: grounding vs. bonding definitions, the single-point bonding rule, and 'four-wire feeder to a subpanel with isolated neutral bar' — three of the most common exam questions in the section.

Quiz — 3 questions