Tank Float Switch Wiring

[carlyai]

I'm rewiring my pumps and have mounted a float switch in the water tank.

The pump from the water tank supplies water to the house and several taps in the yard.

If the tank gets near empty the float switch will operate and open circuit the active connection to the pump, therefore stopping the pump.

Therefore in normal operation the float switch relay contacts are 'made' and 220 V is applied to the pump motor.

I have circuit breaker, OU voltage protection and a switching relay in the circuit as well, but my concern is the water in the tank and the float switch contacts carrying active to the pump.

Is this a normal operation, or dangerous, or should I use the float switch contacts to switch another relay that turns off the motor?

[Crossy]

Assuming the switch is rated for mains use everything sounds OK to me, we have something very similar to control our garden sprinklers (pump from the river, stop the sprinklers when the buffer tank is low).

What is the rating (A) of the float switch and the power (W or HP) of the pump.

[RichCor]

Do you have a make/model on your Float Switch?

There are many types and designs of Float Switches. The self-contained ones are fully jacketed and meant to be water-proof and can carry full voltage (though you should always do periodic inspections to make sure the protective covering hasn't deteriorated or been damages.

[carlyai]

Assuming the switch is rated for mains use everything sounds OK to me, we have something very similar to control our garden sprinklers (pump from the river, stop the sprinklers when the buffer tank is low).

What is the rating (A) of the float switch and the power (W or HP) of the pump.

Thanks again.

The pump is 100 W, but I just had a look in the tank at the float switch and can't see any marking on it. No numbers.

It's one of those blue and yellow ones. May be they come in all ratings?

The electrician bought it when he installed it on the bore pump, for some reason. The bore pump at that time was a 300 W pump. I would hope he bought a correctly rated float switch for the 300 W pump.

I see on some other diagrams of float switches on the web that they switch the neutral.

I have this dim recollection that you shouldn't switch neutrals, or would this be safer?

I also have (will have when I finish building the circuit), an on/off switch that open circuits the active to the motor.

[carlyai]

Do you have a make/model on your Float Switch?

There are many types and designs of Float Switches. The self-contained ones are fully jacketed and meant to be water-proof and can carry full voltage (though you should always do periodic inspections to make sure the protective covering hasn't deteriorated or been damages.

Sorry, I can't see any numbers on the float switch,( it is fully jacketed, there is a little 'M' or 'W' on it), though the electrician bought it when he stuffed up the pump wiring, so hopefully it is correctly reated.

It had been switching the bore pump (previous bore pump 300 W) on and off.

This may be a silly question, but why would you install a pressure operated bore pump, and switch it on and off by turning the power to it on and off?

[Crossy]

There are several varieties of blue and yellow floats, but all the ones I've seen are rated at 220V 10A, so it will be fine on your baby pump.

The only reason I can think of for using the switch on the pressure operated bore pump would be to ensure that it only operated when the tank was, say, 1/2 empty, so not constantly starting up when a little water was drawn off.

[LindaLovelace]

And his other question:

"I see on some other diagrams of float switches on the web that they switch the neutral. I have this dim recollection that you shouldn't switch neutrals, or would this be safer?"

[LindaLovelace]

I will add that I have ALWAYS switched the load, but I, too, just purchased one of these float switches and was surprised to see the instructions saying to run the neutral through the switch.

And having looked at several instruction and diagrams for float switch wiring, I have seen it instructed both ways with comments like: (1) Always switch the hot! and (2) ""Make sure you use the float switch to break the neutral. You don't want to break the hot because then there'd be juice in there. If the float ever fails, you'll energize the whole tank!"

But logically, the latter warning makes no sense because if the neutral is broken instead of the hot, then one side of the switch will be at ground potential, but the other side will still be hot as current passes through the motor windings to the neutral side, even though the motor won't be running.

​So it seems like sticking with the hard and fast rule of switching the hot is of no potential detriment here.

[Crossy]

NEVER, ever, ever switch the neutral, period.

When the switch is open (pump not running) all the pump wiring is live even though it appears to be 'off'.

Ideally one should use a double pole switch but since these floats tend to be single pole place it in the live.

If the float should fail the RCD would operate and kill the power.

EDIT I'm thinking about the switched neutral argument. It could potentially hold the touch voltage of the tank down in the event of water entering the switch, but I'd still stick with the conventional wisdom of switching the live and use an RCD to protect against possible water ingress.

[gundug]

Hi, I purchased one of those blue and yellow float switches (Pro Control Tinnakon) which did not have any paperwork or installation instructions. The diagram on the side of the box shows the blue wire connected to live. Common is then wired to live going to motor. There is a 3rd wire which is brown which I believe is unused for filling a water tank.

Not exactly sure this is correct would be grateful for any advice if there is a better way to wire this switch so that it shuts off a submersible pump when tank is full.

 

Cheers

[Crossy]

9 hours ago, gundug said:

The diagram on the side of the box shows the blue wire connected to live. Common is then wired to live going to motor. There is a 3rd wire which is brown which I believe is unused for filling a water tank.

The switch inside the float is a "change-over" type. Common goes to the motor live, then your supply goes to either the Blue or the Brown depending upon whether you are filling the tank, or stopping it over-emptying (do you want the motor to run when the float is floating or when it is hanging?).

 

It's not difficult to swap Blue/Brown when you get it wrong

 

[lopburi3]

This is normally included with such a switch.  The main thing is to allow room for it to float to upright position to activate switch without getting caught up on wall or pipes and enough room to drop down.  But most people use a submersible pump to drain water/sewerage - not to fill up - must be pump is in a different location?