Path for Neutral Current?

[shortcircuit2]

I'm trying to figure out what path the neutral current will take if the neutral is broken somehow between the generator and the equipment it powers?

I'm referring to all these small residential 7kw to 150kw singe phase units that are not separately derived.

 

[charlie b]

If it is a single phase, 120/240 volt generator, then any current leaving on Phase A will return on Phase B, and vice versa. Any 120 volt loads that are running at the time will split the 240 volts in proportion with their resistances, since they will be effectively in series. That will mean that some might have a voltage well under 120, and others might have a voltage well over 120, either one of which can cause equipment failures.

If it is a three phase, 120/208 volt generator (not related to your question, but I'll mention it just for completeness), then the situation is similar. Current leaving the generator on one phase will return on the other two, and any 120V loads will see out-of-normal voltage levels.

Finally, regardless of whether the generator is single phase or three phase, if the only loads that are on line at the time the neutral breaks are single phase, and all on the same phase, there will be no current, since there will be no complete path for current to follow.

 

[roger]

It will be the same as a POCO service, the two ungrounded legs will become a series circuit and the loads will see current proportionate to their resistance.

Roger

 

[roger]

And what Charlie said.

Roger

 

[shortcircuit2]

Will some of the imbalance seek a path thru the equipment grounding conductor back to the generator source? I'm curious as to the hazards to people or property?

 

[roger]

Will some of the imbalance seek a path thru the equipment grounding conductor back to the generator source?

Not if the wiring was done correctly in the first place.

Roger

 

[Strathead]

View attachment circuit diagram.pdf

First time attaching something hopefully it works. I recently made this up to teach my service guys how to use a meter to identify an open neutral with a meter. I use arbitrary voltages to make the math easier. See what you think. To the OP... As you can see by the diagrams, there is no connection between the ground and either the neutral or the hot wires, so as others stated. No path back to the source for electrons to flow.

 

[brian john]

Not if the wiring was done correctly in the first place.

Roger

And I would wonder how many are correctly installed. Better that 90% of the commercial generators (3 phase wye) we service/see have a 3 pole ATS's with the neutral grounded at the generator and main service

 

[iwire]

And I would wonder how many are correctly installed. Better that 90% of the commercial generators (3 phase wye) we service/see have a 3 pole ATS's with the neutral grounded at the generator and main service

I am missing your point here, yes incorrectly wired systems operate incorrectly.

 

[shortcircuit2]

Thanks for the feedback.

I can see that damage to 120volt equipment would happen in the overvoltage example. Also if a unintendeded neutral to ground bond were at the generator or in the circuit wiring the generator powers, this would provide an alternate path for the unbalanced neutral current.