bonding Neutral and Grounding

[maghazadeh]

Hi to all,
Why do we need to bond Neutral and grounding to gether at elect. service equipment in the the building. I believe the reason is to keep potential diffrenet (voltage) on neutral at zero. If there is any other reason please give me your input.
Thanks
Max

 

[hurk27]

Hi to all,
Why do we need to bond Neutral and grounding to gether at elect. service equipment in the the building. I believe the reason is to keep potential diffrenet (voltage) on neutral at zero. If there is any other reason please give me your input.
Thanks
Max

To have a fault current path back to source, without a connection between the neutral and equipment grounding a fault between any hot conductor and the grounding will place full voltage on this grounding, this will cause the grounding to have a difference in potential between Earth and this grounding, grounding electrodes will not provide a low enough impedance path to cause a breaker or fuse to open so this is why we are required to bond between the neutral and the grounding at the main service, but not after.

 

[mivey]

What hurk said.

I might add that if you meant "zero" as in bringing the neutral down to zero as in the same as far earth voltage: 1,297,352 ground connections and/or rods at the service will not bring the voltage down to zero.

The neutral voltage above earth is a function of the utility neutral, which you are bonded to. The more current that flows on the utility neutral, the more the voltage difference between the neutral and the earth (our "zero" point).

 

[LarryFine]

Another way to put it:

Obviously, a fuse or breaker would respond to fault current from a line-to-neutral short. In order for one to respond to a line-to-ground short, the ground must be connected to the neutral.