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Is my new, 278 ft water well, wired in safely? Electrician ran 100 ft of #6 wire from ( transfer switch out to well house control box ) & then ( 278 ft of 3 wire #12 going down csg to 1 1/2 hp pump ) 378 ft combined wire.

I checked the “Franklin Electric AIM” manual pages ( 14 & 15 ) and the calculations are shown to be acceptable @ .96 maximum allowable voltage drop to meet NEC recommendation of less than 1.0

My issue is that my “Reliance Transfer Switch )has #10 wire running from the 230 volt double pole breaker to the house panel box. So wire starts out at breaker as 4 ft of #10 wire, connected to 100 ft of #6 wire out to well house controll box, then 278 ft of # 12 ( 3 wire ) running down to pump.

The number 10 wire at transfer switch seems too small, but it comes factory wired this way, what do you guys think ?

  • #6 sounds like a bit oversized but it's not a problem, the #10 in a controll enclosure can handle 160a per table 430.72b. The NEC only has a recommendation for a 3% voltage drop for the feeder and 5% at the end of the line but it is not a requirement for the code. What is the breaker size ? Without this we can't say if it is safe. If a 20 amp breaker yes it is. – Ed Beal Mar 17 '19 at 16:50
  • Ed, you are correct about #6 being oversized. The electrician said he could of used #8, but had the #6 at job site, so we agreed on the heavier wire. – Oily Tex Mar 17 '19 at 20:15
  • Yes, both the transfer switch and the house panel are 20 amp, thank you for your reply, Oily Tex – Oily Tex Mar 17 '19 at 20:37
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If the 12AWG submersible pump wire is fine, then the 10AWG in the transfer switch is certainly fine too

A circuit's ampacity is set by the thinnest wire in the circuit. As a result, since we know that there's 12AWG wire in the circuit (going downhole to the pump), the 10AWG wire between the house panel and the transfer switch is fine.

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The wires inside the Reliance transfer switch are part of the equipment, so the size of those wires is judged by Underwriter's Laboratories, not the NEC.

All the NEC says is you must use equipment in accordance with its labeling and instructions.* So if the instructions authorize use of a load that size, you are all set.

The #6 cable out to the well sounds at first blush to be overkill, but it may be overkill for reasons, and it certainly does no harm.

Clearly your electrician is not the kind of person who would run #6 to the wellhead then turn around and run #12 the longer distance down the well. Why the pump manufacturer would insist on #12 is between them and UL. But one thing that does make a difference is cooling: if it is running in water, then water is a fantastic coolant, actually the best coolant yet discovered. Air and dirt are not.


* Because the instructions are part of the UL Listing, which was given because of successful testing. The testing was only done for uses in the instructions; they didn't test it for every possible use (e.g. they didn't test it to pump light crude oil).

  • Harper, yes you are correct, the #6 wire was overkill, electrician said #8 wire would work, but that’s what he had on hand, so we went with that, do to blizzard was fixin to blow in, and trying to do work ahead of bad weather. – Oily Tex Mar 17 '19 at 20:43

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