How deep was a well pump HAVE to sit?

[Zaffer]

I just had a deep well drilled and I’m curious how deep the well pump has to sit to be effective/work well. They allegedly didn’t hit water until about 460’ (at about 4 gpm), but dug the well to 523’ and it’s now getting 6 gpm. It’s a 6” well and static water depth is 45’ from the top of the well head. At 500’, that gives me about 660-680 gallons of water in the well. The well company wants to put the pump at 500’, but is this depth necessary? There are 4 of us in the house and we have 2 horses, but we MIGHT use 40-60 gallons per day, 130 gallons in a day when we fill the water trough, about every 3-5 days. Would I be able to put the pump at 350’ and be fine?

I already ran 12/2 from my panel to the where the pressure switch will be, about 60’, based on the initial estimate of 300’ depth and 1/2 HP pump, but at 500’, they say I now need 10/2 wire to the panel and a 1 HP pump.

Thoughts/ideas?

Please let me know if more information is needed.

Thank you!

 

[Valveman]

It all depends on how fast the well recovers and to what depth. I would test it at about 300'. Pump the well down and see how long it takes to recover and to what depth. Then you can know how much water it will make per day from that depth.

 

[Sponsor]

 

[Reach4]

we MIGHT use 40-60 gallons per day,

That is an unusually low number for 4 people. Still, it is not gallons per day that determines your pump needs.

Planning to use a 3-wire pump with the control box at the well? That will reduce wire needs some.

How long is the wire run to the well?

 

[Zaffer]

The wire run to the pump from the house is 11’, about 16’ adding in the length from the interior wall to the switch. The wire run from the panel, accounting for bends, turns, and endpoints is just shy of 50’, panel to switch.

As for the well pump, the well company only uses 3-wire pumps. I’ve read about advantages and disadvantages for both 2- and 3-wire pumps, so still on the fence with this one.

As for average usage, we try to use water conservatively: we generally take showers every other day, depending, we don’t flush the toilet every time it’s used (if it’s yellow, let it mellow; if it’s brown, flush it down), etc. It might be a little low, but even doubling that would use only about 1/4 of the entire static well capacity.

 

[Valveman]

3 wire motors have more starting torque. Not a bad thing for a pump company to use only 3 wire with control box. But it means they have cycling problems and the 3 wire won't trip off as quickly.

Still need to see how fast and far the well recovers to know how much water you will get and from what depth.

 

[Reach4]

As for average usage, we try to use water conservatively: we generally take showers every other day, depending, we don’t flush the toilet every time it’s used (if it’s yellow, let it mellow; if it’s brown, flush it down), etc. It might be a little low, but even doubling that would use only about 1/4 of the entire static well capacity.

Go ahead and flush.

The 2015 AIM manual says you can run 12 gauge a total of 400 ft for a 1 HP pump.

So with that short path to the well, you have 300-some feet down the well.

You could also run 12 to the well, and use bigger wire down the well.

With 1/2 and 3/4 HP pumps, you can run the wire 650 and 480 ft respectively.

What does take more GPM is if you get a backwashing iron filter. Otherwise a 5 gpm would usually be sufficient. 5 gpm pumps cost more than 10 gpm pumps because they have more stages.

 

[wwhitney]

I already ran 12/2 from my panel to the where the pressure switch will be, about 60’, based on the initial estimate of 300’ depth and 1/2 HP pump, but at 500’, they say I now need 10/2 wire to the panel and a 1 HP pump.

If your only concern is redoing the 60' of 12/2, that's probably not necessary. You can just run the rest of the circuit with #10 or #8.

One random website I checked says that for a 3-wire 1 hp single phase pump, #12 is good for 371 ft, while #10 is good for 592, and #8 is good for 937 ft. If those numbers are applicable, then 60' of #12 uses up 60/371 = 16.2% of the allowable voltage drop.

Which means you have 83.8% left for the rest of the circuit. With #10, the rest of the circuit could be 83.8% * 592 = 496', while with #8, the rest of the circuit could be 83.8% * 937 = 785'.

Cheers, Wayne

 

[Zaffer]

My main concern is what depth the pump needs to be as that will determine what size pump I need and what size wire. So far, the comments have been extremely helpful!

Isn’t 6gpm the rate at which the well refills? If that’s the case, why would it matter at what depth the water refills if static level is ~44’ below grade? We’re not going to use more than 100 gallons at any one time as that’s the size of our water trough. Wouldn’t 300’ pump depth be enough? That would give me approx. 350-400 gallons of water above the pump.

I don’t have a way to pump the well down before deciding the above, unless someone has a good suggestion…..

 

[Zaffer]

I have decided to install the well pump at 300' and see what happens as far as draw down and refill. If it is not enough, I will then drop the pump to around 400'. The well is 6gpm, which I assume is the rate at which the well itself fills and the static level is 45 feet, which would give me 370 gallons of water above the pump; I would not use that much water in a single day, even with filling our water trough for our 2 horses.

I do have some questions, though.

I am looking at getting an RPS 1HP pump and their One-and-done Poly installation kit. The pipe they are providing is rated at 160psi. Is this strong enough for a 300' well or should I get the kit without the pipe and get 300' of 200psi?

Is 200psi rated poly okay to use at 400'? The well company that drilled the well was going to put the pump at 500' with 250psi rated poly.

Thank you!

 

[wwhitney]

If I understand correctly, you need to look at the pump curve for the pump you will be using, and look at the maximum head it can produce at 0 gpm. If your well water level ever dropped down to the well pump level, and the flow was very restricted, that's the maximum pressure your pipe could experience.

Also, 1 psi = 2.31 ft of water head. So when the water level is 45', if your pressure tank is at the same elevation as the well head and set at 40/60, say, the total head would be 45' + 2.31 * 60 psi = 184 ft of head. Plus while flowing water the resistance you have from the pipes, which could vary widely depending on the details. So that will give you an idea of where on the pump curve the pump will operate under those conditions. If the water level falls, then the total head goes up, meaning the flow will go down.

Cheers, Wayne

 

[Zaffer]

If I understand correctly, you need to look at the pump curve for the pump you will be using, and look at the maximum head it can produce at 0 gpm. If your well water level ever dropped down to the well pump level, and the flow was very restricted, that's the maximum pressure your pipe could experience.

Also, 1 psi = 2.31 ft of water head. So when the water level is 45', if your pressure tank is at the same elevation as the well head and set at 40/60, say, the total head would be 45' + 2.31 * 60 psi = 184 ft of head. Plus while flowing water the resistance you have from the pipes, which could vary widely depending on the details. So that will give you an idea of where on the pump curve the pump will operate under those conditions. If the water level falls, then the total head goes up, meaning the flow will go down.

Cheers, Wayne

Here is what it says on the website:
"05RPS series pumps are designed for low flow applications of 8 GPM or under. They can be self-installed or placed using a local installer. At 300 feet of head the 05RPS10 will pump 6.5 GPM! Up to 500ft Head, 3 to 8 GPM"

I would imagine, based on the above, that this should be fine for what I am looking at. I may go down to 350 - 400 feet just to be on the safe side, but wouldn't mind being at 300 feet from an installation/replacement standpoint.

Anyone have any additional information on the rest of my prior post about the poly drop pipe?

​

 

[wwhitney]

"05RPS series pumps are designed for low flow applications of 8 GPM or under. They can be self-installed or placed using a local installer. At 300 feet of head the 05RPS10 will pump 6.5 GPM! Up to 500ft Head, 3 to 8 GPM"

Here's the webpage for the 05RPS10:

RPS 1HP 05RPS10, Up to 500ft Head, 3 to 8GPM, Deep Well Submersible Pump End + 1HP 220V Motor + Starter Box

Power up your water system with the RPS 1HP 05RPS10 Deep Well Submersible Pump End. Reliable, durable, and free shipping over $100. Browse and shop today!

www.rpswaterpumps.com

If you go to "SPECS" part way down the page, you can get to a link for "RPS Water Pumps Spec Sheet + Pump Curves"

That document on PDF page 8 gives the pump curves for each of the model. For example, the 3/4 HP 05RPS07 hits about 475 feet of head at 0 GPM. That translates to 475/2.31 = 205 PSI. So I would think if that the model you select, you would want 200 PSI pipe.

[If I understand correctly, this is a very conservative approach. During normal operation, the pipe will never see 475 feet of head.]

Cheers, Wayne

 

[Fitter30]

You hired a professional that knows the area. If you have a problem at 375' you will on the hook for everything that is needed to make it right.

 

[Zaffer]

I FINALLY got everything installed and running. The pump is a 1-1/2 HP pump at 300’, pushing 9 GPM as measured with a timer and 5 gallon bucket.

As for wiring, the kit came with 300’ of 10/3 wire and then I’m running 20’ of 12/3 to the control box and then 40’ of 12/2 from the control box, through the switch, to the panel with a 30 amp breaker. Is this okay or should I replace the 12/3 and 12/2 with 10/3 and 10/2? Based on previous responses, the 12/2 and 12/3 should be okay.

 

[wwhitney]

Is this okay or should I replace the 12/3 and 12/2 with 10/3 and 10/2?

What does your pump manual say as far as the allowable length for #12 and for #10?

One random web site I checked says for a 1-1/2 HP 3-wire single phase pump, #12 is good for 320 ft, and #10 is good for 510 ft. If your pump manual agrees, then you have used 60/320 + 300/510 = 78% of your allowable length limit. Which is obviously fine, as it's less than 100%.

Cheers, Wayne

 

[Bannerman]

running 20’ of 12/3 to the control box and then 40’ of 12/2 from the control box, through the switch, to the panel with a 30 amp breaker. ... should I replace the 12/3 and 12/2 with 10/3 and 10/2?

Most electrical codes require 10 gauge or larger wire for 30 amp circuits. The usual limit for 12 gauge wire is 20 amps. The intended load as designed, will normally be 80% of the breaker rating.

Because you are using 12 gauge conductors to supply a 30 amp circuit directly from the main panel, and then to the control box, if an electrical inspection where to be performed, it's likely the installation would require utilizing 10 gauge conductors directly from the panel.

Based on previous responses, the 12/2 and 12/3 should be okay.

An undersized wire supplying the pump directly, typically results in a 'soft start' for the pump due to the smaller conductor causing a brief current restriction while the pump is undergoing start-up. During intial start-up, most electric motors consume substantially higher current compared to the current consumed while running under load.

While this forum is intended to provide advice and recommendations on specific topics, it is adviseable to always check requirements with local authorities and obtain any required permits before proceeding with any work.

 

[wwhitney]

Most electrical codes require 10 gauge or larger wire for 30 amp circuits. The usual limit for 12 gauge wire is 20 amps. The intended load as designed, will normally be 80% of the breaker rating.

These limits do not apply to motor circuits. It is common to have a motor that requires only 20A circuit conductors on a 30A or larger breaker. On HVAC unit nameplates, this is the difference between MCA (minimum circuit ampacity, or wire size) and MOCP (maximum overcurrent protection, or breaker size).

The reason for this allowance in the NEC is that startup currents of a motor may nuisance trip a smaller OCPD, and the motor is required to have its own overload protection that is in line with the conductor size. Which overload protection can use a time-current curve different from a regular breaker, a curve more suited to the motor current profile.

Cheers, Wayne

 

[SuperGreg]

3 wire motors have more starting torque. Not a bad thing for a pump company to use only 3 wire with control box. But it means they have cycling problems and the 3 wire won't trip off as quickly.

Still need to see how fast and far the well recovers to know how much water you will get and from what depth.

How does a three wire have more torque? It was my impression that the only difference is where the starting capacitor is located (in the motor or in a control box). No?

 

[Reach4]

How does a three wire have more torque? It was my impression that the only difference is where the starting capacitor is located (in the motor or in a control box). No?

Franklin 2-wire motors have no capacitor, and they are (or at least were) considered more reliable than most other 2-wire motors (Faradyne and Grundfos). I don't know if there are actual studies to bear that out.

 

[RetiredInGueydan]

How does a three wire have more torque? It was my impression that the only difference is where the starting capacitor is located (in the motor or in a control box). No?

The 3-wire control box contains a run capacitor and a large start capacitor that cannot fit into a pump. This gives a robust start unlike the the soft start of the SQ.