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#8251 - 03/14/02 07:19 AM causes of stray voltage
motor-T Offline
Member
Registered: 11/10/01
Posts: 280
Loc: Girard, Ohio, USA
The electrical utilities do all of the wrong things relative to stray voltage. They consider ground to be the same as neutral and they connect the primary neutral and the secondary neutral together at their distribution transformers. The neutrals are then connected to water pipes and building structure of the building. All this results in the potential of the building structure and piping being elevated to the voltage level of the utilities neutral conductor. This is the primary cause of stray voltage on a farm. The good news is that this kind of stray voltage can be eliminated quickly and cheaply by insisting that the electrical utility separate the primary and secondary neutrals on your transformer.
--- The above is from a " Stray-Voltage" site--
Is it me or does anyone else have a problem wiht the way the above is written. I believe its 250.24(c) that requires the neutral to be bonded at the service. They suggest Isolating the neutrals of the primary and secondary of the pole distribution. Which the PoCo does for farmers in my area free of charge, the poco, calls it a 'Neutral Blocker'.
I got a call from a dairy farmer who had a stray voltage in his Milking Parlor. Most Farms in my area have what is described as a 'Maypole' in the middle of the yard where the poco attaches there conductors, and from there (they the farmer or his electrician) distribute tri-plex to all the buildings. At all these buildings is a panelboard with a bonded neutral.
The solution I used was to rewire the sub-panel with a 4-conductor and isolated the neutral to help prevent a ground-neutral voltage. The dairy-output is back to normal from what the farmer tells me, so we helped eliminate most of the stray voltage problem.
Has anyone else seen this ? And this 'Stray-Voltage' thing seems to be the latest ' Cash cow , no pun intended.
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#8252 - 03/14/02 11:08 AM Re: causes of stray voltage
ElectricAL Offline
Member
Registered: 10/10/01
Posts: 597
Loc: Minneapolis, MN USA
Neutral Blocker!

I like it. IMHO this ties in with concerns raised around municipal water pipe ground connections.

It's been a while since I've done farm wiring. May I ask, how the block is set up.

Usually the poco transformer is one span away from the "Maypole". The incoming high voltage line has lightning arrester(s) on the transformer, bolted to the transformer can and run down the pole to the earth ground. The transformer can is bonded to the ground as well.

Is the poco disconnecting the secondary neutral to ground connection at the transformer lugs? Is the service neutral's first connection to the earth at the ground rod at the Maypole?
_________________________
Al Hildenbrand
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#8253 - 03/14/02 02:14 PM Re: causes of stray voltage
motor-T Offline
Member
Registered: 11/10/01
Posts: 280
Loc: Girard, Ohio, USA
ElectricalAl:
The neutral-Blocker is what our poco calls it, it isolates the primary-neutral from the secondary neutral.
No the poco does not disconnect their grounding, this site from what I can figure out is trying to sell something, with the idea that stray voltage is the fault of the power company. When I read this I was livid. and of course a 'slick-talking salesman' is going to place all the blame on the poco.
They even bash equi-potential planes as being too expensive and not that effective. Which is only partially true. So Armed with a pocket-full of half-truths these people are making a living.
The trouble is farms are seldom bothered by the local AHJ.

-Mark-
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