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I really enjoy your newsletters and hope you keep up the great work. I have a question about high voltage buried lines. This is concerning some old outside unjacketed concentric primary (7200 volt) buried lines we have. What happens to our customer's secondary voltages in the residence, if the outside concentric (neutral) dissolves away in the soil and we have essentially lost our primary neutral? All help in this area will be greatly appreciated.
Mike Holt's Comment: Bob, I chose not to include your company name to protect them from any liability that might result from this serious problem.
No. 1. As the concentric neutral dissolves, the neutral impedance increases, this results in an increase of primary neutral voltage drop. It's the primary neutral voltage drop that creates what many call stray voltage. Typically, a primary neutral voltage drop of less than 2 volts will not be noticed, but once the voltage approaches 3 and 4 volts, persons in swimming pools will get shocked.
Note: The primary utility neutral is always bonded to the secondary neutral conductor, and the NEC requires the secondary neutral conductor to be bonded to the metal service disconnect. I think this is a dangerous practice when we bond secondary neutral to service disconnect, but it's Code required. I prefer that all services have a bond wire, with the neutral isolated from metal parts, but I'm only dreaming
I have sent out a few newsletters on the topic of stray voltage and I'm working on a case where Con Edison is telling a NYC police officer to take a hike with his 4 volts that is shocking his wife and kids.
Bob, when your customers start calling because they are getting shocked, don't do a Con Ed and tell them it's because they have an inadequate grounding system or that their pool is not properly bonded.
I pity the unfortunate dairy and pig operations, because the elevated primary neutral voltage (stray voltage) will be killing their animals.
No. 2. Your primary winding voltage will change because of the increase in neutral impedance and the loading of the three different phases.
Because your 7,200V system is actually
two wires of a three-phase 4-wire system, some of the transformers primary voltage will
increase and some will decrease, with the secondary voltage following according to the
A fire is often created when the primary
neutral is opened, resulting in as much as 7,200V on the primary neutral, which is bonded
to the premises metal parts!
So basically when the primary neutral impedance increases, you will create a shock hazard (elevated primary neutral voltage), increased equipment failures, reduced equipment performance, as well as a potential for fires in your customers property because of over or undervoltage.
I have lots of hills to climb and hopefully next year I can take the time to write a series of article explaining the utility distribution system. How it works, what happens when the neutral impedance increases, etc.
To my electric utility buddies: If you receive a call from a customer that they are getting shocked when they touch metals parts or their animals are dying because of stray voltage, please don't look stupid by telling them it's their ground problem (hopefully someone at Con Edison is reading this newsletter). Learn more about this issue, visit the customer and either fix the problem or place a neutral isolated at the customer transformer.
I suggest you review some of the following located on my website:
P.S. It's 4 am and I'm working very
hard on my 2005 products, so please forgive any grammar, typo, spelling errors, etc.
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