Voltage drop for pump waaay down there.

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WattsaVA

Member
Location
Blountville, Tennessee
Occupation
Electrician
I have a job where this guy has built right up on top of a very steep mountain and his water will not pump all the way up there, so he has an “in-line pump" being installed about half way up (1000’ elevation rise with a half mile long driveway).
I need to install the wiring and calculated the voltage drop. For 500 feet it says that I have to upsize to a #3 AWG for a 30A 240V pump. That is four wire sizes increase. I have never been in this situation before and this blew my mind. I knew that I would have to derate it but I thought that it would be one size maybe. #10 to #8.
I read around and found something that I had never heard before and is a little mind blowing too. Supposedly you can increase the voltage considerably to offset, so please help me to understand and tell me if this is incorrect. I can get them to install a 120V pump and run it on 240V and reduce the current by half? Do they even make 120V pumps for this? Also, I don’t know what the voltage or current of the pump is yet. I am just assuming that it is 240V 30A.
Any advice would be greatly appreciated.
 
You need to know the hp of the pump before you start sizing wires for it no matter how long of a run.
You can't run 240V to a 120V pump no matter how long the run.
A better design is to run a feeder to the pump location and put in a small panel.
Someone will jump in here and talk about using transformers for stepping up the voltage at the house and stepping back down at the pump. I'm not a fan of that for this application even if you did need to run #3.
 
What is the difference in elevation between the ground at well and house?
1,000 ft is the length of the supply water line, right?
Wondering if you could put a higher head well pump and pump up the hill to water tank, then a small VFD pressure pump. Just pump 2 gpm up the hill to keep friction loss low
 
Running your system at higher voltage can be a useful way to overcome voltage drop issues, but you can't just throw a 120V load onto a 240V supply and expect things to work.

1) You have to guarantee that in all conditions of operation, the voltage supplied to the load stays in the safe operating range of the load. If you put a 120V load on a 240V circuit hoping that voltage drop will eat up 120V, you are asking for trouble (and destroyed hardware). But if you put a load that can use anything between 120 and 240V on such a 240V circuit, then it will _tolerate_ a huge voltage drop. (This will work for universal voltage lamps, not typical pumps.)

2) Selecting a higher voltage version of the load means that the load will consume less current and have less of a voltage drop issue. If you were in the process of choosing between the 120V or 240V version of the pump, you would pick 240V for lower voltage drop. If you could use a 480V pump that would be even better.

3) If you can select a smaller load that operates on a continuous basis, that will greatly reduce your voltage drop issues. @tom baker expressed an approach to this, and I think it is pretty common for deep well pumps. So it should probably work for this application.

4) Voltage doubling VFDs for pump applications are a thing. 240V in to the VFD, 480V 3 phase out to run the pump.

-Jonathan
 
Also, don’t assume that the pump motor nameplate is actually 240V, that is your “distribution voltage”, what the utility supplies at the service drop. Motors, especially pump motors, are often designed around what’s called a “utilization voltage”, because they EXPECT a voltage drop. So your pump nameplate likely says 230V, not 240V, and that sometimes can make a difference in wire size.

Also also, most VD calculators will default at sizing to attain 3% VD or less, but in reality, motors are usually designed for +-10% of their nameplate voltage with insignificant change in performance. So if you have a 230V pump motor, it is typically going to be fine with as little as 207V at its terminals. Keep that in mind too. This is especially true of in-line pumps because they are being cooked by the water flowing past them. YMMV however, so check with the pump mfr. by getting the pump data before designing the system.
 
Thank you for the input. The entire water supply line is 1000’ elevation rise according to customer. The in-line pump will be installed “about half way” up the hill. So, that would be a 500’ elevation rise between the pump and the house. The customer said that he is guessing that is where the plumber will want to put the pump. The plumber has not seen the situation yet.
I think, though, that Jraef has probably solved my situation with his input. That sounds very logical to me. I replugged the numbers into my lunar space map and it came back and said that with 9.01% voltage drop on 230V, I can run a #8 AWG. It says 20.717 actual less volts. So that would leave 209.28V which sounds like that should be okay with +/-10%.
Extremely grateful.
Thank y’all for the expert input.
 
Well pumps typically come with conductor size charts based on the total branch circuit length. Not sure if inline pumps are similar, but it would make sense.

What is the source 1000' below the house, and what pressure does it provide? If it's a municipal water line providing say 80 psi, that's only 185 ft of head (1 psi = 2.3 ft), so the first pump would need to be at most 185' above the source, or at least 815' below the house.

If it's a well, it could have a well pump that would generate enough pressure at the surface (at the desired flow rate) to get the water half way up, that would be 216 psi for a rise of 500'. But in that case I would think you would be asked to provide power for the well pump also.

1000' of rise is 433 psi, so this is going to require multiple pumps or else some pipe with a really high pressure rating.

And what is the power source at the top of the mountain? If it's utility power at the street end of the driveway, it doesn't seem like it makes sense to run power all the way up to the house and then back down again to power the pump(s).

Cheers, Wayne
 
ActionDave said:
You need to know the hp of the pump before you start sizing wires for it no matter how long of a run.
You can't run 240V to a 120V pump no matter how long the run.
A better design is to run a feeder to the pump location and put in a small panel.
Someone will jump in here and talk about using transformers for stepping up the voltage at the house and stepping back down at the pump. I'm not a fan of that for this application even if you did need to run #3.
Click to expand...
Good advise, for five hundred feet of wire length I'd tend to agree, if it were a 1/4 or 1/2 mile of wire I would explore a 600V step-up and a 600V pump controller among other options.

WattsaVA said:
I think, though, that Jraef has probably solved my situation with his input. That sounds very logical to me. I replugged the numbers into my lunar space map and it came back and said
Click to expand...
And I thought I was the only one with one of those lunar space maps!
 
Hold on there, those numbers seem whacky. A half mile drive (2625') and 1000' rise end-to-end would be an angle of about 20 degrees (!!) or 38%(!!) and that's quite steep, even 10% on a road is considered a lot. Also, I hope you're using a quarter mile (1313') for the VD calc, not 500'.

And @wwhitney makes some excellent points about pressures. Most high-rise buildings use multiple pumps and tanks to get water to the upper floors.
 
The driveway circles around about 3/4 of the mountain. The customer said that it is 1/2 mile long, so the driveway is not straight up the side of the hill, but it is still extremely steep. With his fresh new gravel in my two wheel drive truck I was not sure that would make it up there. And it was a drop off if you ran off the driveway. Very scary if you are afraid of heights (Just because I have a lunar space map doesn’t mean that I am not scared of heights).
 
What we want to confirm is the estimated circuit legnth from the source service panel to the load is as you stated 500' of wire one way.
 
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