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paging MrMark and his hot ground
- Thread starter mrb
- Start date
MrMark
Well-known member
Poco came out yesterday with troubleman and a couple techs and the troubleman seemed to understand. They checked handholes but the transformer vault was full of water and they didn't have the equipment or men to pump it out. They are coming back Monday with a pumper and then they can get in there and check the neutral.
I am still puzzled by this, though. Because if the neutral at the transformer is loose or corroded -this is at the start of the run - that would increase the impedances of both paths (water pipe path and neutral wire path) equally and the current would continue to split according to the normal pattern. It almost seems like there has to be a second path back to the grid along the water pipe. I have never really been able to account for the current flowing back on the water pipe. In other words, I don't see it anywhere that I can look.
Bring that truck down with some ChiCom tools and we'll "git r dun."
I had to open the vault for them with my Snap-on breaker bar. True story.
I am still puzzled by this, though. Because if the neutral at the transformer is loose or corroded -this is at the start of the run - that would increase the impedances of both paths (water pipe path and neutral wire path) equally and the current would continue to split according to the normal pattern. It almost seems like there has to be a second path back to the grid along the water pipe. I have never really been able to account for the current flowing back on the water pipe. In other words, I don't see it anywhere that I can look.
Bring that truck down with some ChiCom tools and we'll "git r dun."
I had to open the vault for them with my Snap-on breaker bar. True story.
MrMark
Well-known member
Could the N current on the water pipe get back to the grid by going back through the neutral of another nearby transformer? I've got to draw up what I am thinking about.
BTW, Edison men had never seen this before, but stated that they would never check water lines on a call, either.
BTW, Edison men had never seen this before, but stated that they would never check water lines on a call, either.
MrMark
Well-known member
The current is going down the next block and then coming back to the transformer. This transformer supplies at least two blocks and is situated at the intersection of these two blocks.
The thing I still can't fathom is why we have not seen significant voltage fluctuations.
the isolation ****** is ineffective to curb the problem unless every house on the service has the isolation ******. The house with the iso ****** will still put current on the water line through the N j-bar where the connection is common with the neighboring houses, which are not isolated.
The thing I still can't fathom is why we have not seen significant voltage fluctuations.
the isolation ****** is ineffective to curb the problem unless every house on the service has the isolation ******. The house with the iso ****** will still put current on the water line through the N j-bar where the connection is common with the neighboring houses, which are not isolated.
Last edited:
MrMark
Well-known member
Well, the tests showed the current going up the one block and coming back to down to the transformer. The transformer has two outgoing three wire feeds, one going East, one going West. One feed for a block. Neutrals tied together on a j-bar at the center tap. A jumper was run from the first handhole N to the transformer N (to test for a problem between the transformer to the first house - or the last house for the N current depending on how you look at it) and it had no impact. Current still running down the water pipe up the next block and swinging back to the N j-bar from the other blocks feed.
Our water main is presenting itself as an incredibly low impedance path where N current is dividing anywhere from 30-50 percent onto the water pipe path.
Kind of perplexing, really. But it all has tested out OK.
Our water main is presenting itself as an incredibly low impedance path where N current is dividing anywhere from 30-50 percent onto the water pipe path.
Kind of perplexing, really. But it all has tested out OK.
MrMark
Well-known member
Could the N current on the water pipe get back to the grid by going back through the neutral of another nearby transformer? I've got to draw up what I am thinking about.
BTW, Edison men had never seen this before, but stated that they would never check water lines on a call, either.
answer is no, current must return to the source transformer.
cowboyjosh
Well-known member
- Joined
- Mar 11, 2010
- Messages
- 1,066
I haven't thought this thru too much before responding, but wouldnt you think this fault would blow the fuse ahead of the utilities transformer at some point?
answer is no, current must return to the source transformer.
does the primary have a grounded conductor? If so, the current could travel to the other transformer, across the primary neutral, and back to the neutral of your transformer.
MrMark
Well-known member
only two phase wires come into the transformer vault and the transformer. There is probably three phase on the main run down the street (three wires) but only two wires tapped for the transformer. Does that make sense?
I just looked up the resistance of 2/0 aluminum and from the NEC its DC resistance is 0.159 ohms per thousand feet. The run from the last house to the transformer is probably 20 feet. We are talking essentially zero resistance. I doubt we could even measure it without special equipment. The water pipe is 6 inch iron pipe. I need to test a sample to get its resistance. Then we can see if this current divider makes any sense.
I just looked up the resistance of 2/0 aluminum and from the NEC its DC resistance is 0.159 ohms per thousand feet. The run from the last house to the transformer is probably 20 feet. We are talking essentially zero resistance. I doubt we could even measure it without special equipment. The water pipe is 6 inch iron pipe. I need to test a sample to get its resistance. Then we can see if this current divider makes any sense.