Switching sockets by contactor from fused spur

[lct]

Only one contactor required:
View attachment 320350

google for "auxiliary contact" and images.

Is this a mad idea - I'm sure it's bad practice, but any reason it would not work? If I happened to have a 3-pole contactor available, 2 poles to switch the pump, and the third pole to use as the Aux for the coil voltage? Or on a 2-pole, only switch the pump live and use the second pole for Aux?
I know it is not hard to get a contactor with Aux contacts, I'm just thinking though minimizing the component count.

 

[Sparky3]

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....

A locked box can stop that.

At the end of the day, it's what you want to spend on reliability, your money.

We had the 3 probe type on 3 sumps, one caustic tank, one hydrochloric acid tank and a discharge tank running 24/7 on a vital process. The only time we had trouble was when somebody threw a bucket of water over the probe head.

 

[Sparky3]

Is this a mad idea - I'm sure it's bad practice, but any reason it would not work? If I happened to have a 3-pole contactor available, 2 poles to switch the pump, and the third pole to use as the Aux for the coil voltage? Or on a 2-pole, only switch the pump live and use the second pole for Aux?
I know it is not hard to get a contactor with Aux contacts, I'm just thinking though minimizing the component count.

And overcomplicating it. Why reinvent the wheel.

 

[Harry Bloomfield]

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.

To experiment with.....

E = longest earth probe; H = high (short)/ start probe; L = lower (longer)/ stop probe.

Find a mains to 12v transformer and two 12v ac relays. Connect one relay, as a latching relay 2, with one side of latch to E, other to H.

Connect your second relay 2, coil powered via E and L, with a pair of N/O contacts in series with the coil supply to the 1st relay.

Water shorts E to L, relay 1 energised. Water continues to rise and shorts E to H, which powers the pump. R1 then remains powered, until the L probe loses contact with the water.

Much depends upon the size diameter of your probes, and the conductivity of the water. The using ac, not dc, is important, to avoid electrolysis and the formation of H and O on the probes.

 

[Harry Bloomfield]

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.

Almost! Short middle probe to long, nothing happens - THEN short middle probe briefly to long, pump runs and continues to run, until short is removed from middle probe...

Easy to get confused..

 

[Sparky3]

Almost! Short middle probe to long, nothing happens - THEN short middle probe briefly to long, pump runs and continues to run, until short is removed from middle probe...

Easy to get confused..

Lol yes,

Been retired 4 years and the memory is going fuddled.

 

[Harry Bloomfield]

Lol yes,

Been retired 4 years and the memory is going fuddled.

It took me a while to work it out too

 

[SUNRAY]

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.

All that happens is it starts pumping, that's what it's designed to do.

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.

Ah well now you're talking. Their density/partical sensor... Mwah

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.

I was on site for some control panel mods during building works. When I got the room was flooded to more than welly boot depth due to a broken pipe on the cold water booster set.Their submersible pump got the flood level down fairly quickly after isolating the pump. But the building work had blocked off the sump drain. It was decided to do a temporary sump pump arrangement using a washing machine pressure switch (off the wharehouse shelf) connected to the top of a length of 1 inch vertical hose. It was amazingly effective for a temporary botch.

 

[SUNRAY]

Is this a mad idea - I'm sure it's bad practice, but any reason it would not work? If I happened to have a 3-pole contactor available, 2 poles to switch the pump, and the third pole to use as the Aux for the coil voltage? Or on a 2-pole, only switch the pump live and use the second pole for Aux?
I know it is not hard to get a contactor with Aux contacts, I'm just thinking though minimizing the component count.

Most contactors are 3 or 4 pole so yes it's ok and some incorporate an aux contact too, example:

It's the sort of thing I may possibly have in the bottom of a box of redudndant stuff.

 

[SUNRAY]

To experiment with.....

E = longest earth probe; H = high (short)/ start probe; L = lower (longer)/ stop probe.

Funny thing is most put E in the middle

Find a mains to 12v transformer and two 12v ac relays. Connect one relay, as a latching relay 2, with one side of latch to E, other to H.

Connect your second relay 2, coil powered via E and L, with a pair of N/O contacts in series with the coil supply to the 1st relay.

Water shorts E to L, relay 1 energised. Water continues to rise and shorts E to H, which powers the pump. R1 then remains powered, until the L probe loses contact with the water.

I haven't tried that but I wouldn't have expected the water to be that conductive.
Yes deffo ac, very critical.

Much depends upon the size diameter of your probes, and the conductivity of the water. The using ac, not dc, is important, to avoid electrolysis and the formation of H and O on the probes.

The probes I'm accustomed to are 2-3mm dia and coated with a tough paint/laquer and colour coded for different fluids, again I always kept the offcuts as I found uses for them.

 

[Sparky3]

Funny thing is most put E in the middle

I haven't tried that but I wouldn't have expected the water to be that conductive.
Yes deffo ac, very critical.

The probes I'm accustomed to are 2-3mm dia and coated with a tough paint/laquer and colour coded for different fluids, again I always kept the offcuts as I found uses for them.

Our probes were all stainless steel.

The water becomes very conductive with impurities in it.

 

[Harry Bloomfield]

Our probes were all stainless steel.

The water becomes very conductive with impurities in it.

The probes I came across, were heavy galv steam pipe, hung from a porcelain insulated top hat thingummy, used for massive pumping and drainage schemes.

 

[lct]

Thank you everyone for your help and suggestions. I have now acquired a Crouzet HNM liquid level relay and planning the other parts to wire it up as a panel.

I learnt some things about contactors today, I always assumed they were relatively simple things and had never had need to look at utilisation ratings. I thought a 16A 2pole would be more than adequate, given the pump is on a regular 13A 3-pin plug. But these 'household 20A' contactors are only rated to 6 or 7A for inductive loads. I think I should play it safe with a 40A contactor, rated to 15A for AC-7b household inductive loads. I'm also considering an industrial 3-phase 16A AC3 contactor, surely AC3 rating (squirrel cage motors with breaking during normal running of the motor) is as good as AC-7b (motor-loads for house hold appliances) and I can just use 2 of the 3 poles. Still hunting for a bargain.

One more decision - the Crouzet works on 24V - 240v. I guess my instinct is to use 24v, given there are probes dangling in the water. But the power pack is another component that might fail so I will most likely stick with 240v, assuming I get a matching contactor. On the other hand if I stumble on a decent contactor with 24V AC coil I may revert to the power supply option.

 

[SUNRAY]

Am I correct thinking this is a 1500W pump?

Any contactor with an AC3 rating of 6A will be fine. If this is commercial any motor over 370W should be correctly protected with an appropriate overload

Which fits directly on the side of the contactor (excuse the mixing of makes which should not be done in actual use.

and all 3 passes through the overload must be used in order for the thermal element of the device to respond correctly.

Another variation goes before the contactor and acts as an MCB but still requires 3 passes of the load current.

Personally I'd fit either one regardless of whether it is commercial use as the pump is left unattended for automatic starting.

In reality the contact rods will be working at a much lower voltage than the supply, IIRC the rule is something like 6V or so. I wouldn't be worried about running it on 230V.
If you do use 24Vac for relay and contactor, do get a control transformer rather than SMPS for reliability.

 

[lct]

Am I correct thinking this is a 1500W pump?

Any contactor with an AC3 rating of 6A will be fine. If this is commercial any motor over 370W should be correctly protected with an appropriate overloadView attachment 321998
Which fits directly on the side of the contactor (excuse the mixing of makes which should not be done in actual use.View attachment 322002 and all 3 passes through the overload must be used in order for the thermal element of the device to respond correctly.

Another variation goes before the contactor and acts as an MCB but still requires 3 passes of the load current.
View attachment 321999

Personally I'd fit either one regardless of whether it is commercial use as the pump is left unattended for automatic starting.

In reality the contact rods will be working at a much lower voltage than the supply, IIRC the rule is something like 6V or so. I wouldn't be worried about running it on 230V.
If you do use 24Vac for relay and contactor, do get a control transformer rather than SMPS for reliability.

Is it a 1.5kW pump, usually left for remote starting on just a float switch. The whole purpose of this exercise is to provide easier setting of hi and low levels, and to avoid potential for the float switch to get snagged. I intend this control box to simply power a socket on/off. It should result in fewer starts per hour than the float switch as we can then utilise the full depth of the sump.

My thinking here is that so long as the contactor itself is not the weak link then the overcurrent protection continues to be just as provided by the 13A fuse that will still be present on the pump plug (maybe10A, haven't checked). I need to leave the pump workable on any socket in case it needs moving location, so hard wiring is not an option.

If I did opt for additional protection in the panel then would a regular single pole MCB on the live just prior to the contactor do the job? I guess these are not as adjustable, but given it is a domestic pump without FLC data on the nameplate its going to be a bit of a guess what to set the overload to anyway, although I could measure actual current in operation.

On the contactor rating - can you shed any light on this rating below? This was my initial pick (cheap, available in Screwfix) before checking the spec. You see for AC-7b it is rated for 9A, but only 1.2kW. So I conclude this is not suitable for a 1.5 kW pump. Are AC3 specified contactors so different that when plated at 6A they are good for 1.5 kW of inductive load?