Electric Shock from Neutral Wire?

[burgerking]

Assume:
Grid's Neutral is bonded to a Grounding Rod in the Main AC Disconnect
My electric gears are grounded (chassis are connected to a grounding wire to the grounding rod)
The neighborhood receives (High Leg) 3 Phase power from these two transformers. I assume the Right Transformer as 208V, Left Transformer as 120-0-120V. Green wire is Neutral; it runs from the very top of the electric poles to other electric poles.



Here is my problem:
Assume somewhere in the neighborhood the neutral wire leading to this electric post snapped!
These transformers will then have no true Neutral, and its only return path are the neighborhood's individual Grounding Rods.

Obviously our Grounding Rods do not provide perfect conduction for power; I suspect our "Ground Wires" would have higher potential than the ground we are standing.

What is the solution for this?

 

[John Frum]

q: how do you reconcile your thread title with the content of your post?

 

[timselectric]

The transformer creates the neutral. I'm not sure what you are asking. Granted, it must be bonded to be called a neutral. The wire traveling up and to the next pole, is carrying the neutral (along with the hots) to other service drops. (Houses or commercial buildings)

 

[burgerking]

If the top wire is severed, transformer's high voltage wire no longer has return path to the Power Station but will instead go to the NEUTRAL WIRE into main disconnect box into grounding rod of each houses.

The transformer's primary and secondary shares the same NEUTRAL wire.

 

[CoolWill]

If the primary neutral broke on the setup you have, the two transformers would be in series with each other and the secondary voltage would fluctuate based on the load of each phase. If the neutral at the service is bonded properly, the local potential to ground would be equalized. The shock hazard inside the building would be none if the service neutral is properly bonded.

 

[timselectric]

It's more likely to go down the pole to the rod at the bottom. That's path of least resistance. (In its attempt to get back to the source) but the transformer would have no output. Because of the loss of input.

 

[efficientPV]

This is more common than most people think. Stick a rod in your front yard and pour some water on it since it won't be that deep. Run a wire to your service ground and measure the voltage. Seeing a couple volts won't be unusual. I had a tree trimmer knock down my power lines. I had tried for years to get the utility to replace them. They were from the 40's and were bare metal and sagging. The floating neutral which resulted took out my refrigerator, microwave, dishwasher, clock and DVD player. Finally got my lines replaced. Seven months later some of my lights are flickering. Went down to the service panel and L1 and L2 were unbalanced to neutral. I take a ladder to look at the incoming lines. The black tape on the crimp is split from heating. Utility guy pulled on all three connections and the came out. Prior installer used the wrong crimp size. This is an old house with copper line to the street. That wasn't enough additional ground to carry neutral current. What I had seen was about 30V on the neutral. Mike Holt has done some videos on running a wire from one utility pole to another and measuring voltage potential.

 

[Spunky]

If the primary neutral broke on the setup you have, the two transformers would be in series with each other and the secondary voltage would fluctuate based on the load of each phase. If the neutral at the service is bonded properly, the local potential to ground would be equalized. The shock hazard inside the building would be none if the service neutral is properly bonded.

Good observation with the series transformers (cluster bracket that they're mounted to would keep them bonded).
And "if the neutral at the service is bonded", is a big 'if'. I've found multiple failures of redundant connections in the grounds outside of homes having broken neutral issues (bright/dim light call).
Besides the primary side (of the transformers) being in series, the secondary sides are connected and will backfeed each other depending on their loads also.
In the city, there are lots of neutral connections. Even though the primary phases many stop, the system neutral may continue to the next circuit or go around as part of a loop. But in a rural area, I've seen a system neutral down in the woods on single phase spur with no voltage issues (didn't check for primary voltage, but have put these back together many times and have seen no sparks), just got called in as a wire down by a hunter. So ground rods seem to be enough for the primary current to return to the sub station. Secondary current just doesn't seem to work as well. Every now and then, I'll find a part power with only one leg and no neutral working fine.
Your word 'fluctuate', is the true answer. How conductive is the pole, did the cluster bracket chip away some cement and contact the reinforcement wire rods? How good are the remaining grounds, neighbors copper plumbing or cable TV messenger wires.

As a Lineman, I bond in multiple places. That X2 neutral bushing on that 120/240 lighting transformer should have a ground strap connecting it to the front of the case.

Losing the neutral to the house is something we find almost every day. Depending on that one wire going through the trees doesn't always workout.