Float switch wire volt drop

[bigspark17]

Hi guys and gals.

a job that has got me second guessing my calculations. I have been asked to fot a float switch to a pump not a problem but the distance is 525m. Now there is no load on the float switch as i will be using a contactor to switch the pump Locally. So can i use a small 1.5mm 2c swa. I see no reason not as there is no load to take into account.
with the cable being so long it affects the price alot should it require a larger cable.
Thanks

 

[David Prosser]

Is the float to be fitted at the pump so it only runs if there's water in the stream or to be fitted at the tank end so pump runs when tank level drops to certain level ?

 

[bigspark17]

Is the float to be fitted at the pump so it only runs if there's water in the stream or to be fitted at the tank end so pump runs when tank level drops to certain level ?

there will be a second float switch in the bottom tank to stop dry running yes.

 

[Wilko]

Hi - over that distance I would also look at a radio solution perhaps? Here‘s a link to one that might work, tx and rx modules would be required but should still be half the swa cost.

MULTILINK, 230V RADIO SWITCH TRANSMITTER ONLY FOR MANY TO ONE APPLICATIONS

MULTILINK is a radio link which replaces "switched live" cabling from one or many locations (manifolds) back to one point (heat pump), wiring in your MULTILINK transmitter to your individual manifolds. When power is switched (on/off) at any MULTILINK-TX (Transmitter), an RF signal is sent to the...

www.rfsolutions.co.uk

 

[pc1966]

Agree that 2-core SWA is a simple and adequate solution. Supply can be protected by something small as well, even a 1A or 0.5A C-curve MCB (Hager make them, probably several others) or similar fuse if you want to be sure you meets ADS as well as RCD protection. I don't think you will easily get a RCBO below 6A though, and ideas?

Personally if budget provides for it I would go wired as more likely to be reliable than a battery/solar panel wireless set up. Providing the cable is safely buried of course!

 

[Lucien Nunes]

Personally I would use SELV to the float switch, a little 24V transformer and a relay operating the contactor. It will be much more tolerant of moisture ingress at the float switch and any repair joints that have to be made, it avoids the 5-10mA leakage that will occur through the cable capacitance at 230V (guesstimate figure, I don't have data for SWA capacitance to hand) no electrical wear on the float switch, etc. You can fuse the thing at 500mA or whatever but nothing harmful would occur with any kind of cable damage, just the pump running or not running. You could even pick up the severed ends and twist them together while live (that's not a recommendation).

On the subject of abnormal operation, one might build in a watchdog timer that stops the pump and lights the alarm beacon on the control box if it runs for an excessive time. E.g. twice the time it normally takes to fill the tank completely. This would detect a variety of possible mishaps and prevent them escalating, e.g. leaking tank or pipe, stuck float switch, clogged pickup strainer.

 

[pc1966]

Yes, having a 48V or even as 24-0-24V to feed the switch and relay/contactor coil is probably a safer and more reliable option.

 

[David Prosser]

Ultrasonic level control with two heads will let you control what you need and will also have the ability to detect broken pipes etc. The heads work effectively up to 1000m from the unit.