Why Bond the Neutral and Ground Wire in the Main Panel
In a properly designed circuit, if a fault were to occur on the 120-volt outlet between the hot-wire and the ground, the current will flow through ground wire back to the main panel, where it will move to the neutral wire via the neutral-to-ground bond, up to the utility transformer, back down the hot wire to the circuit breaker, tripping the breaker. In a faulty designed circuit, if a fault were to occur on the 120-volt outlet between the hot-wire and the ground, the current will flow through ground wire back to the main panel, where because it does not have a neutral-to-ground bond, the current will be forced through the ground rod, into and across the earth, and up the utility ground rod and into the utility transformer, back down the hot wire to the circuit breaker.
In a properly designed circuit, if a fault were to occur on the 120-volt outlet between the hot-wire and the ground, the current will flow through ground wire back to the main panel, where it will move to the neutral wire via the neutral-to-ground bond, up to the utility transformer, back down the hot wire to the circuit breaker, tripping the breaker. In a faulty designed circuit, if a fault were to occur on the 120-volt outlet between the hot-wire and the ground, the current will flow through ground wire back to the main panel, where because it does not have a neutral-to-ground bond, the current will be forced through the ground rod, into and across the earth, and up the utility ground rod and into the utility transformer, back down the hot wire to the circuit breaker. The resistance of the earth is almost always to great to allow sufficient current flow to trip the breaker, and you end up with a steady-state ground fault, that never trips the breaker, and this is a hazardous situation indeed. You cannot use the earth as a conductor.
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