Reading 310 volts on a 120 240 volt residential system

[snoogins1236]

Hi , today I wired up a 240 volt well pump, with a neutral, and phase to phase I read 310 volts. One line has 240 to ground/ neutral and the other line has 120 to ground/ neutral.

It originates from a fused knife switch disconnect where I have good readings of 120 and 240 on both line and load. Further on the load side there is a controller with a capacitor Bank with relays that talk to the holding tank for the well pump. My instinct is that the capacitor is sending extra voltage on one of the lines but I can't be sure because of the type of pull out pins/ plugs that this controller has. I ran out of time today so I will get this thread some pictures tomorrow when I return but I was scratching my head. Thanks for any and all. Help/insight

 

[winnie]

Where did you take these readings, and was the motor running at the time?

 

[ptonsparky]

Hi , today I wired up a 240 volt well pump, with a neutral, and phase to phase I read 310 volts. One line has 240 to ground/ neutral and the other line has 120 to ground/ neutral.

It originates from a fused knife switch disconnect where I have good readings of 120 and 240 on both line and load. Further on the load side there is a controller with a capacitor Bank with relays that talk to the holding tank for the well pump. My instinct is that the capacitor is sending extra voltage on one of the lines but I can't be sure because of the type of pull out pins/ plugs that this controller has. I ran out of time today so I will get this thread some pictures tomorrow when I return but I was scratching my head. Thanks for any and all. Help/insight

Find and read the installation instructions before you own it.

 

[jim dungar]

Is this a VFD controlled pump.
Capacitors are not transformers, they do not just provide extra voltage.

 

[ptonsparky]

230 volt well pumps do not use a neutral.
Take a picture of the controller, along with the label.

 

[qcroanoke]

Find and read the installation instructions before you own it.

After all my years in QC the one absolute rule I had was: did you read the manual? What did it say?

 

[ptonsparky]

Although I did work with a VFD powered at 120v with a voltage doubler and out put of 240 volt three phase.

I doubt that's what you have, but possible.

 

[qcroanoke]

Is all this new?
I'm wondering if you have a 3 wire pump? Or is it 2 wire?.
Ptonsparky. You've dealt with a lot of pumps.
me? Very few.
Could he have or need a 3 wire pump?
Which requires a controller?
2 wire or 3 wire?

 

[ptonsparky]

Is all this new?
I'm wondering if you have a 3 wire pump? Or is it 2 wire?.
Ptonsparky. You've dealt with a lot of pumps.
me? Very few.
Could he have or need a 3 wire pump?
Which requires a controller?
2 wire or 3 wire?

Not enough more, but yes, three wire single phase pumps are common and they do need a controller.

 

[fastline]

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.

 

[Eddie702]

Shouldn't a 240 volt pump have a 3 wire H H EG? not a neutral.

 

[ptonsparky]

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.

I didn't know where he was getting the voltage. Sounds right.

 

[ptonsparky]

Shouldn't a 240 volt pump have a 3 wire H H EG? not a neutral.

No neutral but yellow wire in the cable.

 

[fastline]

I didn't know where he was getting the voltage. Sounds right.

Part of the architecture of a typical pump start is a potential relay that uses the back EMF of the pump to switch out the start circuit and capacitor. Generally speaking, anything larger than 1HP usually also has a run cap that stays in circuit to utilize the start winding for some extra go.

 

[fastline]

Shouldn't a 240 volt pump have a 3 wire H H EG? not a neutral.

Yeah, I think he is understanding it all wrong. Sort of scary. I've seen quite the butchery in the field.

 

[qcroanoke]

Yeah, I think he is understanding it all wrong. Sort of scary. I've seen quite the butchery in the field.

I havent wired a well pump in decades. Is it breaker to pressure switch to controller to pump?
Don't beat me up too bad.......

 

[fastline]

I havent wired a well pump in decades. Is it breaker to pressure switch to controller to pump?
Don't beat me up too bad.......

That's the path.... Always good to have a handle on the plumbing side as well because I've lost track of how many pumps were either murdered or needlessly replaced. One of the most fun as of recent was a family members very new pressure tank with a slow bladder leak. I had to go all the way to corporate OEM because the idiot plumber didn't want to buy my diagnosis.

 

[ptonsparky]

I havent wired a well pump in decades. Is it breaker to pressure switch to controller to pump?
Don't beat me up too bad.......

I'm definitely out of practice and CRS is hitting hard.

 

[qcroanoke]

That's the path.... Always good to have a handle on the plumbing side as well.

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!

 

[ActionDave]

Shouldn't a 240 volt pump have a 3 wire H H EG? not a neutral.

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.