Thread: 240 volt breaker

One more question about neutrals etc. You have helped me understand bonding and grounds very well and I hope this question does not prove that wrong.
Since the neutral is what causes the breaker to trip or fuse to blow I understand that on a 120V circuit it the neural is open it will not operate. On a 240v circuit a neutral is not needed for the equipment to work so what causes the breaker to trip if the neutral is open.
Hope this makes sense.
Thanks

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Originally Posted by Paul Johnston

Since the neutral is what causes the breaker to trip or fuse to blow I understand that on a 120V circuit it the neural is open it will not operate.

Further explanation needed:

"I understand that on a 120V circuit it the neural is open it will not operate."

With the neutral open there could be a significant ho-to-ground ground fault which would still cause the breaker to trip. The ground fault current being sufficient to trip the breaker.

With the neutral open the equipment will likely not operate - unless there is a significant neutral-to-ground ground fault.

That is where GFCI protection comes into play. It the current in the neutral and hot conductors are not with 5.0 ma +/- 1 ma (4 ma to 6 ma) of each other, the GFCI trips.

But only when the circuit is GFCI protected - of course.

On a 240v circuit a neutral is not needed for the equipment to work so what causes the breaker to trip if the neutral is open.

What causes at breaker to trip can be several things:
- the equipment itself fails, allowing/drawing too much current through the equipment itself, as the equipment fails it burns up and "shorts" out, with a "short" being between "hot" and "neutral" causing too much current and the breaker trips
- something allows/causes the "hot" to touch or leak over to "ground", which creates a "ground fault" (versus a "short), and a significant "ground fault" could cause too much current to flow and the breaker trips
- something allows/causes the "neutral" to touch or leaks over to "ground", which creates a different type of "ground fault", and with the neutral still intact, current is going through both the neutral and ground, or with the neutral open the current is going through ground only, and, as the equipment fails (see first reason listed) and the current increases and the breaker trips

Kind of simplistically stated (meaning I know there will be some who will correct it to being stated a better way, which will be good), but that describes some ways for the breaker to trip.

On a basic 240 volt circuit with no neutral , it is the ground that clears the fault. ( trips the breaker).

If the circuit had no ground the only way the circuit would trip would be a phase to phase short. ( hot to hot)