Reading 310 volts on a 120 240 volt residential system

I leave plumbing to those who know how.
My cousin is a master plumber. I call him with plumbing he calls me with electric. Easy peezy!
That's sort of the issue that gets me involved. ECs do their thing, plumbers the other, but you really have to work both. What I find mostly is "pump guys" that sort of understand both, but largely lacking in electrical. Check valve on top of pump end, pitless adapter, pipe issues down hole, etc. Most common is pressure tank issues that certainly cause bad pump behavior, leading to pump failure, then never properly addressed.

Kinda have to know the full system to get them fixed up right. Generally if I end up on scene, it's 'after others', so that makes it worse, but my mission is always to first make the call if the pump has to come out or not. The cause is not always as urgent as making the pump pull plan. Usually I have suspects in minutes like "pump/motor coupler is likely blown". I guess I know what I'm looking for.
 
A domestic single phase pump can be two or three wire + EGC out to the pump. Some use a starting cap up at the well house (3 wire), others put everything in the pump.
No, 'some' don't have a cap at all in the pump motor. I have my own preferences but I've seen plenty of 2 wires live a long life. their issue is nasty inrush currents.
 
No, 'some' don't have a cap at all in the pump motor. I have my own preferences but I've seen plenty of 2 wires live a long life. their issue is nasty inrush currents.
That’s where a planned VD can be helpful in making for a softer start. I never had to be involved with that, but the Franklin AIM manual has lots of good info.
 
I do a fair amount of work with residential well pumps. Around here almost all systems will have a separate pressure pump and well pump.

Mostly 3/4 and 1 hp single phase well pumps, with a start cap in the control box. Yellow wire in the riser cable is for the start cap.

I always have a low water shutdown wired in series with the pump, and the well
pump is activated by a float switch in the tank.

I discourage direct well pump to pressure tank setups. Even here on the rainy north coast of California, we will go 6 months with no rain, so water storage tanks are a necessity. And it’s far easier to replace a pressure pump in a well house than pull 200’ of pipe, riser cable, and pump, when it wears out.
 
That’s where a planned VD can be helpful in making for a softer start. I never had to be involved with that, but the Franklin AIM manual has lots of good info.
You have to be careful as you can blow the triac start circuit if the starting elements are in too long. I do need to play with some PTC tech to see if I can dial some 2 wires back. I can't go too far into a few things because I am actually 'very' deep in pump tech and working on some solutions to ongoing issues in the field.
 
No, 'some' don't have a cap at all in the pump motor. I have my own preferences but I've seen plenty of 2 wires live a long life. their issue is nasty inrush currents.
They do have two wires + EGC run to them so in terms of how many wires go out to the pump it's the same as if it had a cap in the pump, ergo, everything is in the pump.
 
Thanks to everyone for the helpful comments.

Just to clarify, I have a three-wire pump. Two hots a neutral and ground. I have not made it back on the site yet but I will make sure I take due diligence and take pictures of the disconnect, The controller and the readings at the junction box outside at the well pump.
I wish I had a manual! All I had was an invoice with the pump number on it and I wasn't able to find the manual in the field on my phone. This is a old setup, 30 plus years. The owner supplied the pump stating that it was a one-for-one direct replacement of the existing.

I also saw this post on Reddit. Someone also had similar readings on a residential system and claimed to have old batteries in a multimeter. I am also going to try to swap my batteries and see if I get any different result before I go ahead and tear everything apart. https://www.reddit.com/r/AskElectricians/s/CjKx3Xd0Bw

Stay tuned
 
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Some forward-thinking electricians would have taken a neutral out to the pit or well house so they could plug in a heat lamp to keep the pressure switch from freezing. Yes, they just tapped off one of the hots. Better than the usual tap to the EGC or worse, the well casing or ground rod.
 
Thanks to everyone for the helpful comments.

Just to clarify, I have a three-wire pump. Two hots a neutral and ground. I have not made it back on the site yet but I will make sure I take due diligence and take pictures of the disconnect, The controller and the readings at the junction box outside at the well pump.
I wish I had a manual! All I had was an invoice with the pump number on it and I wasn't able to find the manual in the field on my phone. This is a old setup, 30 plus years. The owner supplied the pump stating that it was a one-for-one direct replacement of the existing.

I also saw this post on Reddit. Someone also had similar readings on a residential system and claimed to have old batteries in a multimeter. I am also going to try to swap my batteries and see if I get any different result before I go ahead and tear everything apart. https://www.reddit.com/r/AskElectricians/s/CjKx3Xd0Bw

Stay tuned
Sounds like you are building a nice fireworks display. You DO NOT have "2 hots and a neutral" for the pump.
 
We can't touch those holes. Not even supposed to take the cap off. I could call my local well guy and he could give me permission via phone. It would save him a trip if I could fix it.
Trust me, some just shouldn't...... There I was, standing over a hole with the EC and homeowner. EC could not figure out how to hang the new pump into the pitless. I evaluate and ask questions. Then I ask to see the old pump, in which I confirmed the EC went postal pulling pump out and smacked the pitless face with the pump and broke the ear off. Whole yard needed dug up to replace the pitless now. To make it worse, I confirmed the old pump was good......

Honestly they are not complicated, but about 100 ways to F it up!
 
I work with pumps. He sounds like a rookie messing with a 3 wire pump and 'controller" (really just a pump start). Probably reading back EMF. The controller does not talk to the tank. He is probably talking about wiring to the pump pressure switch.
Or, its a 3 phase submersible with a single phase feed and a cap based static phase adder, and the readings are taking place at the phase adder, and/or there is a problem with it.
 
UPDATE, SOLVED

Pump guy came out and confirmed correct wiring And it is in fact the capacitor producing this increase in voltage.

Thanks to all who had constructive insight and criticism. Hopefully everyone has learned something new!

Pictures are linked here. I swear they are not spam but the forum would not let me upload them directly from my phone
 
I work with pumps. He sounds like a rookie messing with a 3 wire pump and 'controller" (really just a pump start). Probably reading back EMF. The controller does not talk to the tank. He is probably talking about wiring to the pump pressure switch.
Sounds like you've got more to learn
 
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