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.
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.
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.
“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.
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.
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.