Switching sockets by contactor from fused spur

[lct]

This is a little different - I want to build a small control circuit to turn on flood pumps when a high level float switch is tripped, and leave the pump on until the low level switch is broken. I figure this can be done with a couple of contactors inside an enclosure and feeding a regular (outdoor) 13A socket.

My first stab at a concept is below.

Things to note:

- I know pumps come with float switches pre-wired, but the pit depth means long tethers to avoid short cycling the pump and the possibility of snagging the float is too high. Hence this need to build 'fixed' switches to turn on the pump.
- I know I could wire the pump directly into the 20A contactor, but it is important to be able to swap pumps easily.
- The installation will be under an open barn roof, so weather protected. The existing ring main looks to be DIY wired. I haven't been able to check yet, (not my barn) but I am assuming it does come off a 30 year old CU in the workshop that is RCD protected.

Questions I know I would like some advice on. There are probably others things I don't yet know I need advice on, so please chip in if this looks plain stupid:

1) Is this 'allowed' to introduce some home brew switching circuit upstream of a 13A socket?

2) I feel better using 24V on the float switches, although they are rated to 240v, and using 240v would remove the need for transformer and first contactor (changing the second one to 240v coil). Is this practical to step down for switching?

3) Should I fuse the transformer?

4) Would an RCBO inside the enclosure be good practice? Can't be easily reset though, so probably not, even before I get into the difficulty of sizing it.

5) What am I missing?

 

[Harry Bloomfield]

1) Is this 'allowed' to introduce some home brew switching circuit upstream of a 13A socket?

Yes.

2) I feel better using 24V on the float switches, although they are rated to 240v, and using 240v would remove the need for transformer and first contactor (changing the second one to 240v coil). Is this practical to step down for switching?

Yes.

4) Would an RCBO inside the enclosure be good practice? Can't be easily reset though, so probably not, even before I get into the difficulty of sizing it.

Yes.

5) What am I missing?

Look up 'no float' pump control relays. Basically, three metal tubes or rods. One earth, 2nd starts the pump when water touches it, 3rd one stops the pump once the water clears it. There are no floating parts, no flexes to become tangled. Such a relay system can be set up, with a latching and none-latching relay.

Other ways, are to have a pipe, fixed to the side wall of the sump. In the pipe you have a float, with a rod. Upper end of rod has a pair of toggles, one the high limit, the other the low limit. The limits flip a switches arm, on and off, to switch the pump.

 

[Taylortwocities]

Re RCBO inside the enclosure.

I assume that the circuit that the double socket is on is protected by an RCB/RCBO in the house consumer unit? (there should be).
That will provide earth leakage protection. the switched fused spur provides over current protection.
As an RCBO's job is top provide over current and RCD protection then it is pointless. Those functions are already taken care of.

 

[lct]

Look up 'no float' pump control relays. Basically, three metal tubes or rods. One earth, 2nd starts the pump when water touches it, 3rd one stops the pump once the water clears it. There are no floating parts, no flexes to become tangled. Such a relay system can be set up, with a latching and none-latching relay.

Other ways, are to have a pipe, fixed to the side wall of the sump. In the pipe you have a float, with a rod. Upper end of rod has a pair of toggles, one the high limit, the other the low limit. The limits flip a switches arm, on and off, to switch the pump.

Thanks. I'll take a look at the no-float. Only thing I see straight away is a £1 AliExpress module. Concerned on the corrosion of bare metal ends in contact with water for months at a time. .
I would prefer to use robust industrial level switches, but they are expensive, and mostly through-wall. In consumer packages the float switches look to have the best long term reliability.
I do like the idea of a 'column float' because it can be removed for level adjustment. Concern is the robustness of the movement, that it remains free and doesn't snag. I'm only going to be able to inspect the installation twice a year, and I can't rely on the owner being competent to run a good maintenance schedule.

 

[lct]

ANOTHER THOUGHT:

Why am I considering using a FCU? This whole assembly could be with a 3-pin plug, straight into the conveniently located ring main socket. It's then just a switched extension lead. Advantage - no need to open up the ring main for adding the spur (I'm happy doing this, but it's extra work). I can test the new assembly away from location, and easier to remove to modify if needed.

 

[Taylortwocities]

hy am I considering using a FCU?

Not needed.

 

[ericmark]

There are special relays, been years since I worked on pumps, but it was just three rods, one whole lenght of tank, one at switch off point, then one at switch on point, they use to fit on an 8 pin valve base. No need for floats. Only time we used floats was when there was foam on the water.

Some cases just one pair of contacts at top of pump. Once covered pump started one pump started to draw air it stopped, and that's going back pre-1980 sure there is better today.

 

[Sparky3]

Yes, the type @ericmark is talking about are very reliable. The probes are normally stainless steel and work in the dirtiest environments too.

The float type can stick very eaily under dirty conditions.

 

[SUNRAY]

Only one contactor required:

google for "auxiliary contact" and images.

 

[SUNRAY]

There are special relays, been years since I worked on pumps, but it was just three rods, one whole lenght of tank, one at switch off point, then one at switch on point, they use to fit on an 8 pin valve base. No need for floats. Only time we used floats was when there was foam on the water.

Some cases just one pair of contacts at top of pump. Once covered pump started one pump started to draw air it stopped, and that's going back pre-1980 sure there is better today.

This sort of thing.

https://docs.rs-online.com/e7e7/0900766b8106f8ef.pdf

1SVR550851R9500 CM-ENE MIN | ABB Liquid Level Relay - DIN Rail, Screw Mount, Snap-On, 220 → 240 V ac | RS

uk.rs-online.com

Other makes and stockists are available. ie:https://www.ebay.co.uk/itm/38620807...S7jF6gBlrTzAt8hUeBFEZPWonmLFalsUaAnxlEALw_wcB but I don't know the product.


The term to search for is "Liquid level relay."



I have worked with both methods and To be fair I've found both have their problems. The most reliable are the ultrasonic level detectors but very pricey: https://uk.rs-online.com/web/c/auto...YyEQD2yI6R82urGxHHgaAo8aEALw_wcB&gclsrc=aw.ds

 

[SUNRAY]

It's not uncommon to add an additional float switches to add to reliability:

However this will not account for stuck in 'ON' position.

 

[lct]

This sort of thing.

https://docs.rs-online.com/e7e7/0900766b8106f8ef.pdf

1SVR550851R9500 CM-ENE MIN | ABB Liquid Level Relay - DIN Rail, Screw Mount, Snap-On, 220 → 240 V ac | RS

uk.rs-online.com

Other makes and stockists are available. ie:https://www.ebay.co.uk/itm/386208074286?chn=ps&_trkparms=ispr=1&amdata=enc:19FGtExtdS8eRzKYWIZBU-Q75&norover=1&mkevt=1&mkrid=710-166974-033325-9&mkcid=2&mkscid=101&itemid=386208074286&targetid=2236024077829&device=c&mktype=pla&googleloc=1006907&poi=&campaignid=20742287191&mkgroupid=158223592947&rlsatarget=pla-2236024077829&abcId=9330219&merchantid=422128581&gclid=Cj0KCQiAo7KqBhDhARIsAKhZ4ujHQZjnFwdJ13zeQYM_TPWS7jF6gBlrTzAt8hUeBFEZPWonmLFalsUaAnxlEALw_wcB but I don't know the product.


The term to search for is "Liquid level relay."



I have worked with both methods and To be fair I've found both have their problems. The most reliable are the ultrasonic level detectors but very pricey: https://uk.rs-online.com/web/c/auto...YyEQD2yI6R82urGxHHgaAo8aEALw_wcB&gclsrc=aw.ds

Thanks everyone - I'm going to look more at the liquid level relays. I had not come across these before. My first thought is they might be harder to troubleshoot for the inexperienced, and cheaper versions are probably not so robust as cheaper float switches.
The thing that attracted me to float switches is that this is what the £500 pump comes equipped with, and not had any issues with it yet - but had near misses with tangling to maximise pumping volume. Two separate floats on a vertical pole solves that as each has a short flex to its pivot point. Of course the pump switch then needs to be secured in its pumping position (or removed)
Also agree ultrasonic would be a good solution. Use them at work, but exclusively Endress & Hauser and £££. Also not so simple to adjust or troubleshoot. Pressure transmitter sitting in the bottom of the sump is another way, again pricey for a decent unit. Actually what I moved to at work for level control. More reliable than any non-contact probe, especially as dished bottom of tank gets exposed.

 

[lct]

Only one contactor required:
View attachment 320350

google for "auxiliary contact" and images.

Yep - that's easier. Thanks.

 

[Sparky3]

Thanks everyone - I'm going to look more at the liquid level relays. I had not come across these before. My first thought is they might be harder to troubleshoot for the inexperienced, and cheaper versions are probably not so robust as cheaper float switches.
The thing that attracted me to float switches is that this is what the £500 pump comes equipped with, and not had any issues with it yet - but had near misses with tangling to maximise pumping volume. Two separate floats on a vertical pole solves that as each has a short flex to its pivot point. Of course the pump switch then needs to be secured in its pumping position (or removed)
Also agree ultrasonic would be a good solution. Use them at work, but exclusively Endress & Hauser and £££. Also not so simple to adjust or troubleshoot. Pressure transmitter sitting in the bottom of the sump is another way, again pricey for a decent unit. Actually what I moved to at work for level control. More reliable than any non-contact probe, especially as dished bottom of tank gets exposed.

The 3 probe type are eay to fault find. Short long probe to short, pump should start. Short long probe to middle the pump should stop.

Doesn't get much easier.

Don't flood the sensor head though as water in the top shorts all 3 probes and the systrm goes nuts.

 

[lct]

The 3 probe type are eay to fault find. Short long probe to short, pump should start. Short long probe to middle the pump should stop.

Doesn't get much easier.

Don't flood the sensor head though as water in the top shorts all 3 probes and the systrm goes nuts.

The datasheet I was looking at needs sensitivity set up to correctly detect: 3 ranges, fine tuning. Depending on model also to select between pump up and pump down. Once this is done it should be set, but it comes down to not being there and others fiddling....