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#208588 - 01/31/13 11:06 AM stray voltage  
schenimann  Offline
Member
Joined: Feb 2008
Posts: 193
Western North Carolina
I've got a customer that is getting transient voltage to his well pump. He is getting 7-9 volts from pump ground to the ground coming into the pump. The pump doesn't want anything over 1.5v. This burned up their last pump over a year. They are trying to figure this out. I spoke to the pump installer who seems pretty knowledgeable.

They called the power company who came out and checked the voltage and said it was fine on their side. The technician turned off individual breakers and the main breaker without any change. I am going over there tomorrow to look at it. What is the best thing to check. Do I need to disconnect the neutral comming into the panel and check voltage from there to the panel? Any help would be appreciated.


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#208591 - 01/31/13 11:53 AM Re: stray voltage [Re: schenimann]  
twh  Offline
Member
Joined: Mar 2004
Posts: 919
Regina, Sask.
Install a ground rod or plate at the well and tie the incoming ground and anything else that might be isolated to that.

I've seen that issue (transient voltage) before and I don't know of any other solution. The difference in voltage just happens.


#208592 - 01/31/13 12:49 PM Re: stray voltage [Re: schenimann]  
sabrown  Offline
Member
Joined: Dec 2002
Posts: 302
Ogden, Utah, USA
If you have a metal well casing, use it for grounding instead of any of the other methods above. I tend to doubt that this will fix the issue unless you have a long feed to get to the well head, but it is a best practice.

Check all the conductors, you may have an intermittent open or high resistant break in a line or at a connector.

Could you please tell us more about the type of pump. Is it a single or three phase typical motor? or a hybrid type which may have a built in varible speed control and accept multiple voltages and does not care about frequency? Or is it controlled by a constant pressure controller above grade? How long is the feed? How deep is the motor?

I am at a loss myself. With the above information, I still likely will have no better suggestions.


#208593 - 01/31/13 01:04 PM Re: stray voltage [Re: schenimann]  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,120
Estero,Fl,usa
My bet is, if you were in a space ship taking the measurements, the well is ground and the house is 7-9v above ground.
What kind of grounding system do you have at the house? If it is just a rod, I bet that is the problem. What does your clamp show on the neutral from the PoCo with the main tripped?
What do you see on the pump ground the same way? Disconnect the pump ground and see if the PoCo neutral current drops significantly. (be careful here, you might see some volts when you open that)
You may be using the well as the ground for the neighborhood.


Greg Fretwell

#208594 - 01/31/13 01:06 PM Re: stray voltage [Re: schenimann]  
sabrown  Offline
Member
Joined: Dec 2002
Posts: 302
Ogden, Utah, USA
What type of insulation is used on the conductors? RHW or XHHW? I might be convinced that THW or THWN could be culprit, especially if DC voltages are used.


#208597 - 01/31/13 05:35 PM Re: stray voltage [Re: schenimann]  
schenimann  Offline
Member
Joined: Feb 2008
Posts: 193
Western North Carolina
I appreciate all the troubleshooting help. I am going to look at it tomorrow and will check on these issues. I will let you know what I find.


#208600 - 01/31/13 08:01 PM Re: stray voltage [Re: schenimann]  
Tesla  Offline
Member
Joined: Jun 2004
Posts: 1,273
Sacramento, CA
Have I got this right?

I've got a customer that is getting transient voltage [and amperage] to traveling down his well pump [chassis grounding/bonding conductor into the Earth].

He It is getting showing peaks of 7-9 volts from across the pump ground chassis to the ground[ing bond] coming into the pump from the Service.

The pump['s electronic controls] doesn't want can't withstand anything over 1.5v swings in chassis potential. [Making it a floating ground that pumps current in and out of chassis grounded capacitors within its logical assembly.] This burned up their last pump['s integral controller] over a year['s time]. They are I'm trying to figure this out. I spoke to the pump installer who seems pretty knowledgeable.

============

The entire problem is that your bonding run is now part of the GEC assembly -- and you're seeing the effect of a lousy neutral to GEC assembly situation.

Everyone else: be aware. This is now common because of plastic plumbing.

Last edited by Tesla; 01/31/13 08:15 PM.

Tesla

#208601 - 01/31/13 08:26 PM Re: stray voltage [Re: schenimann]  
Tesla  Offline
Member
Joined: Jun 2004
Posts: 1,273
Sacramento, CA
Having run out of edit time...

Another GEC closer to the Service is in order. It is, typically, the most practical way to draw off the amps and volts that are currently shunting their way down the well pump's bonding conductor.

And, that conductor is, perhaps, undersized. There is a strong tendency for such runs to be under engineered -- and to have undersized conductors -- all of them.

The starting draw of a well pump is mighty high. Conductors for such motors need to be sized as if they were to feed the beast -- calculated upon starting draws.

They're such a chronic problem that the NEC ought to have a separate wire sizing table just for them. If not, then a template -- in the manner of HVAC templates -- that stipulates conductors, voltages and distances.

Left to their own calculations, the well boys will always undersize conductors.

It gets down to salesmanship: no-one wants to bring the pain.


Tesla

#208612 - 02/02/13 01:16 AM Re: stray voltage [Re: schenimann]  
schenimann  Offline
Member
Joined: Feb 2008
Posts: 193
Western North Carolina
HO called me this morning to advise that the poco came back out and rechecked. Apparently when he removed the meter and installed his test meter the first time he did not have a wire to ground. I've never dealt with this so I don't have a good understanding of their procedure. After checking it properly, the problem is on their end with a deteriorating line somewhere that they will have to fix. As well as pay for the new pump.


#208613 - 02/02/13 03:43 AM Re: stray voltage [Re: schenimann]  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,120
Estero,Fl,usa
Sounds like what I was talking about. I bet this guy was the ground for the grid (at least locally)

Maybe a copper "collector" took all the grounds off the poles.


Greg Fretwell

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