Grounding Problem

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ElectricianJeff

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I'm curious as to situation I encountered today, I apologies in advance if this turns out to be a long story but hopefully someone can shed some light.

Last Friday evening around 7:00 my wife and I were returning from dinner when I received a phone call from a customer who I had did a 100 amp upgrade a couple of years ago. He said " the wires had burned off his house and he had no power". It just so happened that I was about 10 blocks from his house at the time so I would stop by and take a look at it. This is a overhead service with the transformer on the pole in his front yard. His entire triplex had burnt about 2' from the transformer and dropped in his front yard. They were still hot to the touch when I arrived. I looked at his panel and he had no tripped breakers. There had been no storms that evening. I told him to call the POCO, have a cold one and wait for them to come fix it. It was about 95 degrees at the time. I heard nothing further on this.

Today I got a call from a customer who asked me to come by and look at something. It just so happens this customer is on the same side of the street about 6 houses down from the fellow I visited with on Friday. I had installed a whole house generator from him last summer along with a bunch of small stuff. His cable had gone out on Saturday and the cable guy had been there earlier. He handed me a baggy full of burnt and melted splitters and RG-6 that came from the cable box on the outside of the house. He had no interruption of power on Friday evening. I discovered that the ground wire to the plumbing had been severed near the entrance in the home. He had a new hot water heater installed a couple of months earlier and the plumber had installed a new plastic water line to the new HWH and had spliced in about 2' of plastic in the main line with no jumper. The #4 thhn had either been cut with a hacksaw or may have burned through I couldn't tell for sure. I have trouble believing that the ground saw enough voltage to burn up. There is no ground rod outside since this installation is quite old.

The owner also mentioned that his wifes blender "ran funny" when she used over the weekend which made me think there was a neutral problem and I had him call the poco to come out and check their connections at the pole.. I plan on jumping around the plastic the plumber installed to bond his plumbing along with reconnecting the ground upstream of the splice.

I have to suspect the friday night problem had some to do with his cable box burning up. However he is not on the same transformer as the fellow up the street.

Can anybody shed some light on what happened here?

Thanks
 
The neutral opened at the transformer and current trying to find a path back to the source was carried over the cable TV wire and plumbing etc.
 
All return current will try to get back to its source with all paths available. This will be in relation to impedances of the path.
Since there are rods driver at every few poles or more, there are several paths.
 
No, the secondaries' neutrals could be interconnected by the POCO.

It is curious, or lucky timing, that the 1st house's equipment wasn't damaged when the neutral path (plumbing, CATV, etc.) finally let go, if this is what happened. What did the line ends of the service drop look like? Did they pull out of uncrimped lugs?
 
You must not be married very long...my wife insists on being taken home before I stop on any service calls, even if they are on the way.

No they would not have to be on the same transformer. Somewhere, eventually the neutrals of the transformers are connected together be it earth, waterpipe or cable tv shield.
 
No, What did the line ends of the service drop look like? Did they pull out of uncrimped lugs?

I don't think so, it looked like the lines had just burnt a couple of feet out from the transformer. I saw no signs of a lugs but they may have gone south in the fireworks.

You must not be married very long...my wife insists on being taken home before I stop on any service calls, even if they are on the way.

25 years :) she could tell by the excitment in my voice when the guy said the electric lines had just burnt off his house that we were stopping

thanks for the explainations and besides that I just figured out how to multi-quote :D
 
I don't think so, it looked like the lines had just burnt a couple of feet out from the transformer. I saw no signs of a lugs but they may have gone south in the fireworks.



25 years :) she could tell by the excitment in my voice when the guy said the electric lines had just burnt off his house that we were stopping

thanks for the explainations and besides that I just figured out how to multi-quote :D

I've seen similar issues, when the neutral goes away the service or xformer the unbalanced load current goes wherever it can. The shield on RG-6 coax can carry a surprising amount of current before it lets the smoke out, and the CATV system is usually bonded at dozens of locations in the neighborhood.

BTW, how do you multi-quote?
 
...

BTW, how do you multi-quote?

Click the
multiquote_off.gif
button on each post you would like to quote, in the order you want them to appear.
 
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