A friend is putting in a 3 phase submersible pump. His well is 720ft deep with the pump at about 700 ft. They are concerned about the torque of a large single phase pump twisting the pipe too much. It is only about a 70 foot run to the power source. He only has single phase power, so I assume there is a converter box somewhere. Is it at the well head or at the breaker. He is getting his pump this week so I should know more then, but I am just trying to get ahead and get a little info about previous experience.

Such pumps are usually integral parts of the well casing (pipe). A million mad horses couldn't shake them loose.

Otherwise, get a three-phase pump and feed it through a frequency drive. This will provide a 'soft start' feature.

Most well I useally run into most will have a " toqure arrester " and with 3Ø pump you can invest a soft start or VFD so you can able ramp up without putting in the stress on the pipes.

How big the pump it is ?

Merci,Marc

I'll 2nd the question. how big a pump? and what is it for?

Just to clarify, the starting torque of an AC motor is generally the same regardless of being 3 phase or single phase. The only thing that would make a difference in using 3 phase is if you use a VFD as a phase converter. But 700 feet is a long distance for a VFD run, so make sure your motor and VFD will not have issues with that. You may need what is called a Long Line Filter or at the very least, a reactor on the output.

It's going to be a 3hp pump. It will be his primary water supply for his house and his livestock. The county is actually helping with the cost so that he can get his animals out of and fence off the creek.

If it's a three phase pump with a single phase supply, you're pretty much required to use a VFD ... problem solved.

Why is he using a 3p pump? How much water can a cow drink?

Greg, 700 ft. is a pretty good amount of head. I suspect a single phase motor is both a lot more expensive, as well as considerably larger in size.

Incidentally ... wells are the one place I find the corner-grounded delta service.

How do you deal with the excellent ground rod you just installed, with respect to lightning strikes? When you bond the power system to the well casing, you just made the rest of your electrical system very attractive to lightning.

Larry C

Larry, I bet it is a PVC well casing.

Reno, If he doesn't need a lot of flow, it doesn't have to be that big a motor. He sounds like he just wants to keep a stock tank full, not water a golf course.
If this is one of those Las Curces dairies I retract my statement.

My estimate is that at [say] 80% efficiency, that is allowing for throttling and other losses, a good pump design should be capable of 3Wh/[US]gallon. 3HP would thus give about 2000 gallons an hour. Cows drink/use a lot of water though, next door reckons on at least [converted] 33 gallons a day each. Ergo, 66.66 cows!

I don't see that single phase v 3phase makes much difference to efficiency, the amps in a 3 phase set up are less because of the [usually] lower current carried in each conductor and a 3 ph motor is slightly more efficient electrically. Besides, even at 120v single ph, 3hp only comes to 25A by my reckoning.

As to torque, I suspended my well pump on a thin stainless steel multistrand cable to avoid lifting it out by the power cable.
It's a 1.5hp 4-stage axial turbine type, 230v single phase run at about 25 feet depth at 45psi gauge. Any torque twist on startup is very momentary [just a twitch] and of quite small magnitude, and imho not worth worrying about. I have run this pump free standing in a butt, to test it, with nil twist problems.

Alan

Math correction, Units: That should have read 66 and 2/3 cows per hour, of course.

All the well casings I've ever come across are steel and the lengths are butt-welded as they are sent down the well as it is drilled.

I fail to see how a well-casing if metallic, instantly becomes a risk during lightning episodes, it is of course underground.

The 4 inch or smaller wells are threaded tight when they drive it down { the 4 inch can be either welded or threaded one of the two }

The larger one no question asked automatic butt welding.

The deepest well I ran into with sumbersble verison that go little over 300 meters ( 900+ FT } that have 40 HP motor on it. the supply pipe is 4 inch rigid pipe bezjezz that sonvagunner is very hevey.

One thing I know the code is oversighted on this one they should done in first place get correct bonding conductor that will really elemated all the ground rod issue there.

Merci,Marc

I guess I am just confused about how much head you need on those wells. Around here the wells are typically around 200 feet but they have a static water level from -13 feet in the spring (dry season) to bubbling out of the ground.
We all had shallow well (surface) pumps until the yankees came down and started watering the grass. Sometime when they all turn their sprinklers on at the same time they pull down the static water level so low a shallow well pump will cavitate.
The casings are always bell end PVC that they just glue together as it goes in.

"I fail to see how a well-casing if metallic, instantly becomes a risk during lightning episodes, it is of course underground."

My point is when you bond the electrical system to the well casing, you provide an excellent ground rod. Would this make the electrical system MORE attractive to lightning?

Larry C

Larry: Found this:

http://www.inspect-ny.com/water/WaterWellLife.htm

Last paragraph:

"..Water pump wiring especially for submersible pumps, and the pumps themselves are vulnerable to damage from lightning strikes. It's possible that the combination of electrical wiring and the steel well casing are attractive to lightning, particularly when the well casing extends above ground level (as is common practice with modern drilled wells). Electrical surge and lightning protection systems are available for installation (usually at the electrical panel) to reduce the risk of well wiring or pump damage from lightning.

What does Carrot Top have to say about it?

Inspect-NY seems to be a pretty dubious source. They deal in a lot of conjecture and anecdotal "evidence". Their main objective is printing out home inspection reports that discount the selling prices of houses. Have you ever read their "aluminum wire' tirade. It is basically "run for your lives, it is gonna blow!".

I would say that if you have decent bonding practices the well pump is no more likely to be damaged than anything else. I live in a place with a butt kicking thunderstorm almost every afternoon in the summer and I don't hear stories about a lot of blown up well pumps. We all have wells.

Apologies Greg/all for the dubious link. Ignorance is bliss! Thanks to Google, I was able to find out a bit about Carrot Top and his zany inventions. His take would probably be to put some wheels on the well so you could tow it away in bad weather.

Where I am more concerned is when the structure is the highest point in the area, however the lighting always seem to strike further downhill because the lower elevation trees are more conductive than the higher elevation rocks. A fellow I worked with has this exact situation. He asked my opinion as to whether he needed a lightning rod system. I suggested that he talk to a lightning protection professional, however my personal opinion is that he should not put in a system because the lighting is already not striking his place. I believe that if he adds lightning rods, he will just attract the lightning to his house.

In this situation, adding an extremely good ground rod (well casing) will make his electrical system much more attractive to lightning strikes.

Larry C

I have a little anecdote (I hesitate to call it "evidence" of anything)

I live very close to a 250kv power line and that has always been my lightning rod. The poles are maybe 80-100' above grade.
It has been hit many times. When I put up my weather station I realized I was putting a big metal antenna in the air, maybe 25' above grade so I made an air terminal for the top. It is 3' of 3/8" copper tube with a stainless steel point on top and a 2ga conductor to the GES. It has been hit twice that I know of. Yup dumb old me attracted lightning to my weather station and blew it up twice.
I was in the drive once and actually saw the hit. Exciting stuff huh?
I do believe there is something to that air terminal stuff.
I must say, other than the weather station that has wires running parallel to the lightning rod conductors and absolutely zero lightning protection on those conductors, nothing else was harmed. In real life what blew was the serial port in the PC it is connected to.
I have since put ferrites on all the leads and I am looking into making/buying some opto-isolation.
I have a couple months until the rains again.