I need to install a very long (2140ft distance one-way, X2) DC control circuit run through a float switch to control a 220 vac, 1.5 hp submersible water pump in a well pumping up to a gravity feed tank. Tentative planned installation is a wide angle float switch in the water tank, with a solid state relay of some kind at the well, a DC activated relay of some kind with a low input current for the long run. I was planning or hoping to use the solid-state relay to control the power relay to the pump.Conduit is installed in the ground already.


Anyway I am just now getting around to putting this plan into action and was wondering if anyone out there has any recommendations about a similar or better set-up…? I am no expert I could use some practical/experienced advice on what voltage to run to the float switch for such a long run, what relay, and most importantly what recommended wire size (the smaller the wire size I could use all the better, that much wire will be expensive!) I would like to keep the system as simple and functional as possible and not make it overly complicated! Any help is greatly appreciated.

 

Is flooding and freezing an issue where you are?

It's really more about mechanical and lightning protection than wire size.
http://www.cirris.com/learning-center/calculators/133-wire-resistance-calculator-table

I've direct buried flooded telco cable, with telco protectors on each end.

Even 24awg will be only 110 ohms. So driving a ssr or even a small control relay is no problem.

What is the plan for pulling 2000+ ft ?

 

5vdc will turn on a ssr thru 200 ohms. A 12-24 volt supply will be fine. Even a wall wart.

If you have power available on both ends you can even set up a simple telemetry system with line failure indication.

 

Thanks for the input.

I do not have power available at the tank, I looked into a telemetry system but they get expensive, needs solar power, and just more maintenance and complication involved.

Flooding, freezing, and lighting are not an issue. The conduit has three pull boxes to break up the pull distance plus it's on a steep slope so gravity is working in my favor when I go to pull the wire. I was figuring on a 24 volt power supply and was thinking of using 4 wire telephone cable and twisting wires together into two pair..? Basically looking for some relatively cheap wire that will get the job done. Any recommendations..? Much thanks for the input

 

That will work fine. Even a single pair.

Use 24vdc power, thru .5A or smaller fuses, thru long cables, thru float switch, to ssr.

I have no opinion on grounding one side of supply. The systems I've worked on do not. However they were designed for leased telco pair.

Output of ssr used to pull in line voltage coil on 1.5hp motor starter.

I would also use protectors on both ends. Such as movs. Line to line and line to ground. Or telco devices which use gas discharge components.

 

Any opinions on the differences regarding reliability and simplicity between using a solid state relay to control the pump motor contactor and using use a transistor-driven relay that required only a few milliamperes of current to activate the relay…? Is one system better over the other for a long switch circuit such as this using small wire? I’m just trying to nail down my best option? The transistor-driven relay route was mentioned to me while researching this. Thanks

 

Would a radio link be an option, instead of the wire?

 

Any opinions on the differences regarding reliability and simplicity between using a solid state relay to control the pump motor contactor and using use a transistor-driven relay that required only a few milliamperes of current to activate the relay…? Is one system better over the other for a long switch circuit such as this using small wire? I’m just trying to nail down my best option? The transistor-driven relay route was mentioned to me while researching this. Thanks

If I were doing this I would stay away from transistors and solid state relays. The reason is that 2000+ feet of wire can act like a giant antenna that can pickup impulses from nearby lightening strikes. I would use 12 or 24 volts through the float switch and long wire run to directly drive a small relay which would switch a larger motor starter.

 

Lighting strikes are a rarity but can not to be completely ruled out. I was just leaning towards a Solid State Relay because of the long run wire inductance and trying to keep the wire size down to a minimum size that will get the job done. 4300ft of heavy gauge copper wire would be pretty expensive!

 

The ssr is pretty reliable if you use fuses and protectors, but is still the weak link.

If you use a relay, pick a voltage source/relay combination, that will work thru wire resistance. It will be more critical than a 3-32vdc ssr.

You still need protectors to keep cable insulation from breaking down over time.

Also keep in mind that there will eventually be line failure. Some method of going to "safe" mode with failure is needed.

You may be able to use the second pair for this.
Using a second level switch to lockout system.
Or a lockout timer, if normal run times are known.

 

Here is a preliminary circuit using a second pair and an aux NC float switch to feed a lockout system.

Not saying you need it. I'm just playing with the idea.

It uses a NO ssr to turn off with over flow and a NC ssr to turn off with line short.

A similar circuit may work with the operating float switch to detect a line short.

Edit:
Forgot diagram.

 

A few more things to consider. I assume you are filling a water tank, water tanks sometimes use a dual float setup where one float controls the low water level where the pump turns on, and a second float triggers at the high level which shuts the pump off.
Also, if you go with a low current though the float switch to control the pump relay it's possible to have problems with the electrical contacts in the float switch not always working if the switch is meant to be used in a higher current circuit. It is not reccomended to operate switch contacts at less than 10% of their rated capacity.
You may need to use a mercury switch or maybe a magnetically activated reed switch with gold contacts.

 

Here is preliminary idea for overflow protection with line failure short.

 

And another if you have spdt switch.

This will inhibit pump with:
L1-L2 short
L1-L3 short
L2-L3 short
L1-L2-L3 short

 

Ok have a good idea for the system now. Any recommendations on a good source for some wire? The pulls will be in the six to seven hundred foot range! And we are talking 4300 ft total length so bulk supply is preferable. Thanks

 

Why can't you draw power for the control systems from the power to the motor? In the US, it is quite common to get control power and motor power for small motors from the same supply lines.

Assuming you can do that, why not handle the signals over the same wire, but at a much higher frequency?

John

 

The storage tank is large for fire protect and only has one switch (SPDT (AKA form C) to start pumping immediately after the level starts going down. I'll try the switch I have first, then consider something else should it not work. Thanks for the reminder on that though.

 

I was planning on using power from the motor leg for the relay pwr just used the wrong terminology/power supply when writing. The tank/float switch is off in a completely different direction 2300 ft from my pump power source. Conduits been in the ground for years just now getting to rigging it up with wire for the control circuit. Have been running a mechanical timer but that isn't very efficient I end up wasting a lot of water or not having enough. I have to estimate the run times, a real hassle.

 

What kind of cable do you want?

Have you thought about the three wire/two relay approach? It uses the switch that you have!

 

Can you use the water pressure in the pipe at the pump location to determine the water level in the tank?