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-   -   Can a float switch control submersible pump at well head? (http://www.diychatroom.com/f18/can-float-switch-control-submersible-pump-well-head-156570/)

philS 09-11-2012 10:55 PM

Can a float switch control submersible pump at well head?
 
My well feeds into a 1500-g holding tank. A second pump then feeds the pressure tank and house. A float switch in the holding tank turns the well pump off when the holding tank is full, and on when the water in the holding tank drops to some level.

The well pump is 3-wire with a Franklin controller and a Pumptec to keep it from running the well dry. The controller and Pumptec are located in the house, 100 ft from the well and holding tank.

Question:

Is there a right (or wrong) way to wire the float switch in series with one of the well pump wires so that the float switch wires don't need to be run 100 ft back up to the house to get on the line side of the controller?

My pump guy first wired the float switch into either the start or run wire, I'm not sure which. It worked, but thinking about this more, and asking around, I decided that the switch should be put in the "other" leg of the 240 V circuit. My pump guy agreed, did it, but didn't actually check to make sure it worked. A week later, the holding tank is empty and the well pump has failed. We don't know if the well pump ever worked wired this way. There's 240 V power to the well head, and bypassing the float switch doesn't help. A Megger (of a sort I don;t recognize) says infinite resistance down the well but we have no idea yet if it's a splice or the motor or what.

I'm starting to think there's something important about how the controllers work that neiither I nor the well guy understand. Any thoughts in advance of tomorrow's unfolding drama would be much appreciated.

AllanJ 09-12-2012 07:54 AM

It may or may not be possible to do it the way you describe.

It may or may not be permitted to do it the way you describe.

We need to see schematic diagrams of the controllers and the pump to come up with the solution.

The possible non-permitted method (if it exists) consists of "switching the neutral" although in reality the wire involved, because it is a 240 volt circuit, is not called a neutral.

philS 09-12-2012 10:42 AM

Thanks Allan. I'll get the info and post it. So it's at least possible that we damaged the pump?

philS 09-12-2012 11:23 AM

PumpTec is model# 5800020100, Franklin QD Control box is #2801081915. Don't know pump model # yet. I don't see any schematics anywhere on the web. I may just call Franklin later today, depending on what we find.

Still, any general comments on why this might not work, and/or why it might not be permitted, would be much appreciated. I did some Googling on "switching neutral 240V" and found nothing relevant or helpful. Is there a better term for this than "switching neutral" since that's not what's being done here?

Phil

mpoulton 09-12-2012 12:56 PM

Quote:

Originally Posted by AllanJ (Post 1008278)
It may or may not be possible to do it the way you describe.

It may or may not be permitted to do it the way you describe.

We need to see schematic diagrams of the controllers and the pump to come up with the solution.

The possible non-permitted method (if it exists) consists of "switching the neutral" although in reality the wire involved, because it is a 240 volt circuit, is not called a neutral.

Is there any reason that wouldn't be permitted? Using a single pole switch for a 240V load is definitely allowed, as long as it is for control and not as a disconnect.

J. V. 09-12-2012 01:14 PM

If there is a motor starter or contactor, you have no reason to use one leg of motor power for the float switch. The correct way is to drop out the starter, if you have one.
If you have a starter let us know. I can post a drawing.

mpoulton 09-12-2012 01:18 PM

Quote:

Originally Posted by J. V. (Post 1008433)
If there is a motor starter or contactor, you have no reason to use one leg of motor power for the float switch. The correct way is to drop out the starter, if you have one.
If you have a starter let us know. I can post a drawing.

I think he was saying that the float switch is very near the wellhead, but the motor control unit is in a different building far away. The best solution would probably be to move all the well control equipment to the wellhead and just run power out there, but that's more work than just wiring the float switch to interrupt the pump's common wire.

AllanJ 09-12-2012 01:24 PM

Quote:

Originally Posted by mpoulton (Post 1008426)
Is there any reason that wouldn't be permitted? Using a single pole switch for a 240V load is definitely allowed, as long as it is for control and not as a disconnect.

I don't have the NEC handy but the proposed situation here is comparable to this: We have the usual 12-2 Romex feeding a 240 volt only load. Along the way there is a junction box where only the black wire is switched. At the load, only the white wire is switched.

Just came up with another bright idea. The pump has 3 wires, I am guessing for better or worse one wire is for the starting current, the second for the running current, and the third is the return. After determining that the 3 wires indeed have the roles described, use a two pole float switch to control the first two wires. (Unlike in a typical line voltage thermostat, both switch poles must open simultaneously and close simultaneously.)

joed 09-12-2012 01:48 PM

Its' called a motor CONTOLLER for a reason. It controls when the start winding is energized and when the run winding is energized. You have seen the results of not running the switch back to the controller. Perhaps you can move the controller to the well head? Should not require adding more cable. It might even be that you have an extra wire since the controller probably only feeds from two wire and outputs to three wires.

philS 09-12-2012 02:25 PM

Thanks guys. You nailed it, though it might be called toe-nailing. The float switch can;t go on the "neutral" leg with a 3-wire motor. If it's put there, the controller keeps trying to start the motor when the water level drops and the float switch kicks on. The float switch on neutral side works fine to shut the pump off when the tank is full, but not at the other extreme.

So, today when we checked again, the pump worked fine. The likely answer is that the motor over-heated after repeated energizing of the start winding, and the thermal over-ride kicked in. That's why we got infinite resistance last night, and why taking the float switch out of the circuit made no difference.

The 2-pole float switch (for both start and run) is worth thinking about, though the current wiring seems to work fine.

Live and learn. But I really appreciate the posts. This forum is great.

stickboy1375 09-12-2012 05:22 PM

This isn't complicated, The float is simply breaking one leg suppling power to the pumptec, which then supplies the pump controller, do not break the run or start leg of the pump itself....

joed 09-12-2012 08:17 PM

Quote:

Originally Posted by stickboy1375 (Post 1008557)
This isn't complicated, The float is simply breaking one leg suppling power to the pumptec, which then supplies the pump controller, do not break the run or start leg of the pump itself....

I think you are missing how this is installed. The controller and pumptec are in the house. The switch is out at the well between the pump and the controller.

kbsparky 09-12-2012 09:42 PM

Many float switches can not handle the high amps required to directly control a pump motor.

I'd use a relay/contactor and let the float switch control that instead.

It will last a lot longer, and you won't have the issues with switching only one leg of the pump, and voltage limitations of the switch burning out your motor.

stickboy1375 09-12-2012 11:24 PM

Quote:

Originally Posted by joed (Post 1008659)
I think you are missing how this is installed. The controller and pumptec are in the house. The switch is out at the well between the pump and the controller.

Im not missing anything, I would run a switch leg from point "a" to point "b" and thats the only way I would do it....

This is not a high amperage setup, and the float can easily handle the load.

philS 09-13-2012 01:02 AM

In fact the float switch has been handling the load just fine for 25+ years. If and when it (or the holding tank pump) bites the bullet, I'll replace the switch with a 2-pole 30 A rated one and switch both start and run wires.

FWIW, what this all replaces is a wellhead paced underneath a badly built shed with a 14" crawl space. All my attempts to insulate pipes both above and beneath the floor met with resistance from various critters. They just used the insulation for nest material. Inside the shed, all the wire (mainly romex) was just hanging out exposed. And the whole thing (2 pumps, 120 V lights and outlets) was fed by a 150 ft run of 12-2 UF protected with a 30A (!) breaker.

In the new system I have run separate wires for the two pumps (#10) and another set (#12) for the 120 V part -- an outlet and a thermostat controlled light bulb for heat. There's one #10 ground in the conduit along with rest of the wires, tied to a ground bar in the box at the wellhead (and bonded to the well casing). The whole thing sits under a a large plastic box that I had fabricated for this purpose, on top of gravel instead of dirt. I made some design mistakes in the new system that I'll fix over the winter but in general I think this is a huge improvement.

And with the pressure tank now up in the house instead of 90+ ft down the hill, it may be just coincidence, but all the the water hammer has disappeared.

Any thoughts on how this might be improved would still be appreciated. It's already passed inspection but both the inspector and I are happy to learn from you guys.

Peace, Phil


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