Open service neutral

[The electron man]

Why dose an open service neutral create voltage on the grounding system



I get that current is returning and has no way back to the service neutral and get to the grounding system using the main bonding jumper, but the neutral in the main disconnect is still grounded so how dose this happen

 

[Hv&Lv]

Why dose an open service neutral create voltage on the grounding system



I get that current is returning and has no way back to the service neutral and get to the grounding system using the main bonding jumper, but the neutral in the main disconnect is still grounded so how dose this happen

If you lose a service neutral there is no "regular" path for return currents. The return currents take any path available. Through the grounding conductor, ground rod, RG cable shield or phone lines, anything that's connected to the intersystem bonding Can be a path for return currents if it is connects to ground on the pole or padmount transformer.

 

[infinity]

I get that current is returning and has no way back to the service neutral and get to the grounding system using the main bonding jumper, but the neutral in the main disconnect is still grounded so how dose this happen

Chances are the neutral current is returning on the water pipe to the other services in the area that are also bonded to the water pipe.

 

[The electron man]

Chances are the neutral current is returning on the water pipe to the other services in the area that are also bonded to the water pipe.

Would it use the earth as a conductor since

Like down the rod and up the rod at the transformer

 

[LarryFine]

I get that current is returning and has no way back to the service neutral and get to the grounding system using the main bonding jumper, but the neutral in the main disconnect is still grounded so how dose this happen

It of course depends on the location of the break, but simply speaking,with the neutral open, the electrodes are the only things struggling to keep the premises neutral at the same potential as the utility neutral.

As the premises electrode system is still tied to the premises neutral, the voltage on the local grounding system rises above zero volts as the neutral voltage rises, restrained only by the electrodes and earth.

 

[infinity]

Would it use the earth as a conductor since

Like down the rod and up the rod at the transformer

The earth is fairly poor conductor which is why is isn't relied upon for clearing a fault. Yes some current could theoretically return on the ground rod but if the system is still working somewhat normally with an open neutral it's typical that the current is travelling on the metal water piping systems.

 

[LarryFine]

Would it use the earth as a conductor since

Like down the rod and up the rod at the transformer

It would attempt to use each and every pathway available, current inversely proportionate to impedance.

Picture a hot wire tied to your wrist, and only your fingertips on the ground, like Addams Family Thing.

What would determine the relative current through each finger? That's kinda how neutral systems work.

We want and expect most of that current on the service neutral, but the other currents are always there.