How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask AssuredElectrical Your Own Question
AssuredElectrical, Home Specialist
Category: Home Improvement
Satisfied Customers: 4241
Experience:  35 years home improvement
Type Your Home Improvement Question Here...
AssuredElectrical is online now
A new question is answered every 9 seconds

How can an AC activated low water shut off switch be configured

This answer was rated:

How can an AC activated low water shut off switch be configured to work on a solar powered water pump?

I'm Michelle, and I’m a moderator for this topic.
We have been working with the professionals to try to help you with your question. Sometimes it may take a bit of time to find the right fit.

I was checking to see if you had already found your answer or if you still needing assistance from one of the professionals.

Please let me know if you wish to continue waiting or if you would like for us to close your question.

Also remember that JustAnswer has a multitude of categories to help you with all your needs from Health, Pets, Computers, Cars, Finance, Law, to Home Improvement, and more.

Thank you,
Customer: replied 4 years ago.

Thank you. No, I haven't found an answer yet, but your resources seem to offer the best potential. I should have asked "Just Answer" in the first place if there is a low water switch for a solar pump.


Thank you, XXXXX XXXXX continue to look for a professional to assist you. Please let me know if I can be of any further assistance while you wait.



Customer: replied 4 years ago.

No answer yet.

Hello again,

We are still working with the professionals to find you the best possible match. I wanted to touch base to see if you still needed a professional’s assistance.

Please let me know if you would like to continue to wait or if you would like to cancel your question at this time. We sincerely XXXXX XXXXX the extended wait time.

Thank you,
Customer: replied 4 years ago.

Keep it up. If anybody wants to discuss the issue, I'd be happy to do so. At the moment I have no better resource.

Welcome. My name is XXXXX XXXXX would be glad to assist.

Was the pump working prior to wanting the addition of the float?

Can you wire the pump directly to the panel and run?

Lets start there and move to the next step, thanks
Customer: replied 4 years ago.

The pump is wired directly to, and is powered by, two 2' x 4' solar panels and it works fine. It sits in a 100 gal watering trough that is continuously fed by a usually dependable stream. The pump lifts the water about 80 feet to a storage tank to irrigate a hill-side garden. If the stream supply in interrupted, the pump will run dry, thus the need for a low water shut off switch.

What I finally found is basically a sump pump, but the seller ignored the solar powered part and sent an AC switch. Since it was fairly expensive, I hope I can somehow wire it to work. The switch should open one of the pump wires.


What size pump is this? The rating in wattage or amperage and the voltage?

The output of the solar cells is what voltage?

What is the distance from the cells to the pump? And now, of course from the cells to the switch?

Do you have a model and make on the float switch?

Do you have a multi meter that can read voltage (DC of course) and continuity (Ohms)?

Thanks, XXXXX XXXXX it is a lot of questions, but they all have a relationship to each other and are needed to see what is happening.
Customer: replied 4 years ago.

Yours are all good questions assuming they're relevant to the question. Sadly, I'm in California right now and the pump and its data are on Kauai. I won't be back there until August. I thought I was just looking for how to hook up an AC switch to a DC system, perhaps using an inverter or the AC system itself.

If the answers to your questions are needed, perhaps we can suspend the search until I return to Kauai, in which case I'd need whatever info will get me back to you.


It's a small pump yielding about a gallon a minute at the 80' lift point. I think it turns out something like 17.5 V. The solar panels are about 8 feet from the pump, but the wires are probably 50' long. I was trying to connect the switch directly into one of the panel-pump wires.

I have a multimeter, but I forget what the readings were.

Ok, thanks, XXXXX XXXXX

Lets look at the system now, since we dont have any power information or models.

Is it wired like the diagram below? I assume the panels are parallel wired
to maintain wattage, if series I can change the diagram.

Many components are rated for AC and DC, not that many are AC only.
Difference being, on DC the rating is lower in current because of the arcing
when contacts break open and closed.

The wire length requires an increase wire size for the current draw, but without
any wattage,voltage numbers I cannot tell you the size.

#10 minimum and most likely #8 or #6 since the low voltage will have a major
impact on wire length as the current goes upwards.

It is possible to put a relay between the float and the DC power, so the float
switch operates on AC and it turns a relay on and off for the DC to the pump motor.

Very simple setup, but wiring becomes the issue with AC outside because of the safety
involved so it takes more time to install.

Lets go one step at a time and see if the diagram adds any information to the situation.

Let me know.
Customer: replied 4 years ago.

Excellent! I don't understand much about relays, wattage, and wire length, so that part will have to be clarified when I have the data. I might be able to get someone to read the label on the panels.

They must be wired in series if your drawing is for parallel. If I remember correctly,one wire from panel A goes to B and the other wires from A and B go to the pump. At present, the only way to shut off the pump is to disconnect one of the wires,


The wires, I think, are #12 solid copper rather than wound, but the short cord I used with the plug is regular household extension wound cord, probably #14. If the overall length of the wire from the panels to the pump is a problem, the excess could be cut out. When I said the panels are about 8' from the pump, I should have said closer to 18' as far as the wire connection is concerned, but the overall length of the wire is about 50'.


Your relay suggestion appears reasonable, but I'd have to be able to ask for the right thing and how to connect it. How is wattage and voltage related to whether the system is parallel or in series? Somebody suggested that an inverter like one used to have a car battery operate an 110v electric drill might work, but I can't picture that.


Anyway, I think you're on the right track. You're the first person that seems to understand the issue. Thanks.


Ok, thanks.

If they are series connected then you are boosting the voltage and keeping the current the same as one panel.
New diagram below.

Now, I can tell you with the length of the wire at 50', it maybe too small.
The voltage drops when the wire size is too small, so the pump would run very inefficient and hotter tending to die at a faster timeline than if the voltage is correct.

This is where the nameplates on the panels, pump are necessary to determine proper fit and wire size.

Also, solid wire is not suggested, only stranded wire should be used. Much better conductor and current carrying especially for low voltage DC applications.

Inverter will just change the low DC voltage to AC voltage.
That would allow some AC for operating a relay if needed or change the pump to AC, but think the float switch would work on the DC voltage.

Changing the pump to AC would require more safety in the wiring etc and cause more difficulty because the low voltage is not dangerous for shock hazards, where going to AC would be.

Here again, without a Make and Model, another unknown.

If they can read some labels for you, it would be great.
Solar panels
Float switch.

Get Voltage, amperage,wattage or anything on the label.
Take pictures and then they can be posted right here to look at. Much easier.


Customer: replied 4 years ago.

I'm supposed to rate your answer when I'm 100% satisfied.


So far, your advice has been excellent, but we're not finished yet because I haven't given you all the answers to what you need to complete your advice. This may take some time.


Meanwhile, I'd give you credit with 5 stars. And I think your advice is worth more than the $15 I first agreed to pay.

If the system is notifying you to rate, just ignore that notice/s.
That is a system response with any answers that may be posted and they can pop up from time to time. I have no control and it is automated.

Rating Only takes place when we are complete and all is well and you are satisfied.

Just post when you can provide more information, we will keep at it no matter the time length.
Customer: replied 4 years ago.


Back in business. Here is what is on the back of the panels:


Industrial Solar: Model IS 85J

Operating Voltage: Vmp 17.2 V

Operating current: 4.85A

Open Circuit Voltage: Vcc 21.5V

Short Circuit Voltage: Icc 5.33A


Ok, thanks for the panel info, any luck with the pump or float switch?

I will look into the panels and post later, hopefully you can acquire some more info so I can mate the panels up with the rest.
Customer: replied 4 years ago.

By "luck" with the pump or float switch, I suppose you're asking if they work. Absent any connection to the switch, the pump runs whenever the sun is shining on the panels and the wires are connected.

The switch hasn't been tested independent of the system, but since it's new and the movement of the interior parts can be heard when the canister is tilted from horizontal to vertical, I assume it would work if plugged into a 110 V outlet and a 110 V device was plugged into the switch.

Thanks. Maybe we got mis tracked.

Previously I had asked for the following:
If they can read some labels for you, it would be great.
Solar panels
Float switch.

We have the panels now, but nothing to relate them to as yet.

Not quite understanding the PLUG in the float switch?
Sounds like it is not a stand alone switch but part of a system?
Customer: replied 4 years ago.

The switch came with a short cord, the plug of which has both male and female accommodations. The only instruction is that the (presumed 110V) pump male fitting plugs into the female fitting on the switch plug and the male fitting of the plug goes into the 110V power source.

It seems to be designed to pump out a sump as may be found in a house basement. The switch is in a float that allows the pump to operate as long as there is enough water in the sump for the float to remain horizontal. When the float turns down, the switch is activated and turns off the pump.


Our challenge is to made the switch operate in a DC, solar powered setting, or to find a switch that is designed for that purpose, if the one we have can't be adapted.



Ok, I now know what the float switch is.

You have a piggyback system designed to plug into a receptacle and plug the pump into the back of the same one.
That takes the 120 volts, sends it through to the switch and back again to the backside female receptacle.

There is a lot of resistance in that style and it will only be rated for 120 volts AC and not for a low voltage setup as you are working

You need a different float that is merely a set of open contacts that make and break with water level.

Then wire it like the diagram I posted earlier.

CLICK HERE for an example

Customer: replied 4 years ago.

This appears to be what I should have sought originally.

All the devices mentioned seem to be intended to turn a pump on when a tank gets low. We need it to turn the pump off when the water gets low and back on when the water goes up.

The description of one device tells of changing from normally open to normally closed by reversing the float. Is that what we want and what's all the part about relays and contacts?

The one you need would have open contacts when the water is low and closed when high so the pump runs with water.

Most of the floats have both so it is not a problem and they can work either way, just swap one wire.
To me (manufacturers are very different), normally closed will be closed when low and open when high.
Normally open is opposite, open low and closed high, what you need.

Those 2 were examples only of what you need.

Without the pumps amperage and voltage rating on its nameplate, I cannot pick the one out that would definitely work.

The one I posted you were asking on relays etc was only rated for 1/2 amp, so that is why they mentioned something else to actually activate the pump.

They have higher rated floats to match your pump, but we need those numbers to find yours.

The easiest way is just use a relay and it will not matter what the pump operates at.

Here is a diagram for the wiring with a relay and use either one of the floats I posted, they both will work with the relay.
The relay and base can be purchased here:

Relay base CLICK HERE


Terminal numbers are on the diagram as well.

CLICK HERE for the diagram ( the site still has problems, sorry cant post it right here, have to post the link)
Customer: replied 4 years ago.

Following your advice, my plan is to get the Amico switch, the 781-1C-12D and take them to Kauai along with your diagram, probably in August.

Assuming that's the answer to my question, I quess I'm ready to Rate to Finish.

The last post with the relay setup is the safest at this point, that allow the pump to be any amperage and the system will work with it.
Everything is DC rated and at the low voltage you have so all match the situation.

May change pumps in the future and then would not want to change the setup by using the higher rated float with no relay.

This is probably less costly as well, since the higher rated floats become more expensive with a high DC amperage capability.

If it was mine, that is the route I would take, float,relay,pump.
AssuredElectrical, Home Specialist
Category: Home Improvement
Satisfied Customers: 4241
Experience: 35 years home improvement
AssuredElectrical and other Home Improvement Specialists are ready to help you