Relevant NPFA 70 sections for consideration when sizing a deep well pump

Question

Previously I had little experience with well pumps, but after moving into a home with a failed pump in an area where a shallow pump is at 500', I'm beginning to learn a lot. Recently a pump servicing company pulled up my failed pump, 700' below ground in a 1200' well, and confirmed it had failed at least in part, due to overheating.

My primary concern is that I don't want this to happen again under my watch. I don't expect the installer to honor any warranty even if they do claim it, so I want to make certain the installation complies with the NEC and pump manufacturers specs.

The installed has yet to provide the new pump model but I want to have information before it goes into the ground. The original pump was a 1.5HP PENTAIR 42B0015A2-01 installed in 2019 which so far I have not been able to locate on the manufacturers website. It has a max load of 10.5A with a 10ga wire pigtail. The wire run to it was 700' feet of 8/3 flat cable which has a very thick sheath. I would assume it's some type of direct bury.

What I am looking for is any relevant articles in the NPFA 70 to consider for this type of installation.

Answer 1

I checked my copy of NFPA 70 from 2014. I'm certain that there are no new requirements for water wells since 2014 because I keep up with changes.

Wiring gauge and wire type to a water well pump is not specifically called out by any article number or subsection, so use the same wire gauge rules as for any other motor load.

The type UF wire that you mentioned in your well is not among the prohibited uses for UF listed under 340.12.

A submerged pump motor in a water well is required to be grounded under 250.112(M) and the well casing itself must be connected to the same pump circuit equipment grounding conductor.

Answer 2

For my submersible pump (which is a Myers using a Pentair motor, IIRC) there are extensive detailed charts in the pump installation manual covering wire gauges for various distances and type of pump motor ("2-wire" "3-wire" "3 phase") and size of motor (the manual covers many models of pump with different size motors, as I recall.) I think it also covered pumps with Franklin motors as a separate set of charts.

So, for wire gauge, follow that. NFPA 70 says to follow manufacturer instructions, and there they are. Don't forget to include the horizontal distance to the top of the well as well as the distance down the well. Of course the link is the manual covering your old pump and your new pump might be different. The warranty is 12 months from install or 18 months from manufacture date.

For overheating, main thing I can suggest is a pressure switch with a low-pressure cut-out (if it drops below ~20PSI, it turns off until manually started again.) Pressure tank size as a minimum should ensure the pump runs for 60 seconds. More is better (but costs more.) IIRC (it's been in the hole 12 years or so) the pump motor itself also has a thermal cutout on my pump, so that would also help. None of that is in NEC/NFPA70.

But this is per code, as it's in the instructions:

NOTICE When built-in overheating protection is not provided, install an approved overload equipped motor control that matches motor input in full load amps. Select or adjust overload element(s) in accordance with control instructions. When built-in overheating protection is provided, use an approved motor control that matches motor input in full load amperes.

Code also makes no comment on providing surge suppression for a pump, but I certainly felt it was worthwhile - so much so that I have one set on the panel where the pump is fed from, and another 110 feet away at the top of the well itself. The well casing is bonded to the grounding system, (it's a 100 foot long 6" diameter grounding rod I already paid for once) and the pump has an explicit ground wire. Section 250.112(M) requires the well casing to be bonded to the pump equipment grounding conductor. Section 250.112(L) requires grounding the case of the pump.