Ground wires let breakers trip

Electrical · System Grounding · printed page 91 (PDF page 92)

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Ground Wires let Breakers Trip Electric System – Grounding System Grounding – Electrical

Text in the illustration

to ground
main breaker
service conductors
black (hot) wire shorting against panel box
red wire
neutral wire
ground wire
grounding terminal is bonded to metal panel box
neutral bus bar
neutral bus bar is bonded to metal panel box
bus bars
grounding terminal
since the panel is grounded, the black wire shorting against the metal sides allows the electricity to flow easily to ground (very little resistance) - the resulting high current flow immediately trips the breaker (deactivating the circuit)
if the panel wasn’t grounded properly and someone touched the metal box, electricity would flow through the person (enough to kill them), and possibly not enough to trip the breaker

Generated explanation

The illustration shows an electrical service panel with a main breaker, branch-circuit breakers, bus bars, neutral bus bars, and grounding terminals. Incoming service conductors enter at the upper right, and a grounding conductor exits at the upper left. A black hot wire is shown shorting against the metal panel enclosure. The neutral bus bar and grounding terminal are labeled as bonded to the enclosure, providing a low-resistance fault-current path that allows the breaker to trip. The bottom annotations contrast this protection with the potentially fatal shock hazard of touching an improperly grounded enclosure.