Contactor Pump problem

[GilesA]

A submersible well pump begins pumping when the mercury float switch in the water tank switches on a contactor. It stops when the water level in the tank raises the float and switches off the contactor/pump. For 15 years there was no contactor used and it worked well, indeed with no problems apart from pump replacements. On rewiring last year, the electrician said the law (?) required a contactor to be fitted where motors are switched.

After about a year, the contactor seems to go to sleep now and again. The float switch tries to switch on the pump but nothing happens. When you press the Off/Reset button, the contactor goes in with a bang and the pump fills the tank. It then works for a while but randomly goes to sleep again.

1- What is happening in the contactor to cause this indolence ?
2- Can it be made more reliable or taken out of circuit ?
3- If the top thing is a contactor, what does the bottom thing do ?


Pump - Ebara Idrogo M40/8, Q 20-80l/min, V1 230-240, I 4.3A, P2 0.6kw, HP 0.8, Hz 50, P1 1.0kw, Phase 1, min 2800, F 16, Vc 450, Ip 68.

Contactor - ABB - A9-30-10 4kW 230V - The bottom thing's dials are set to 4 A (2.8,3,3.8,4); Manual (Man/Aut).

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Image

 

[breezer]

mercury float switches have been banned.

modern float switches have a micro switch and giant ball bearing clicky

not all microswithes can handle a lot of current, hence the contactor

your contactor seems to have a timer, i suspect its the timer at fault.

 

[sparkyy]

Theres no timer. What you have under the contactor is the motor overload, which will "trip" if the motor draws too much current. If you are having to press the overload reset button to get it going the motor has tripped the overload. I see the current rating of the pump is 4.3A and the overload is set at it's max 4A this won't help. I suspect that with time the motor is drawing more current, perhaps it's full of gunge, and tripping the overload.

 

[333rocky333]

Not the law but the regs, 552-01-02 says something for motors over a certain size 0.37 kw, that they, require some sort of protection.

If it only trips occasionally you can switch the overload reset mechanism from manual to auto.
You could buy a larger overload unit more suitable for the motor rating

 

[sparkyy]

The overload should be capable of handling the full load current of the motor ie 4.3A. If it's worked ok for a year before starting to trip I still think there will be a reason for it tripping now, build up of crud in the pump housing a bearing getting a bit tight etc. Remember before you change the overload to automatic reset (which resets the overload for you when it's cooled down) clear the fault first. If it continually trips and resets there is a real chance it will burn out the motor.

 

[333rocky333]

Yes, fully agree with that, if it keeps resetting then turn it off.

 

[GilesA]

Thank you very much for your most helpful observations.

So, the bottom thing in the contactor box is an overload switch...
Well, well, well (!)...so the contactor staying off randomly is not the fault itself but merely the symptom. How many times have I gone to fix the symptom, not the fault itself due to mis-diagnosis ? Classic faultfinding idiocy. Thank you.

No, it won't be grunge on the pump as we are on sand - so it is crystal clear water in the well. But it is very hard water and there is always oxide build up on our bore and pond pump shafts. I will pull the pump tomorrow and slot in a spare to see whether that eliminates the behaviour.

Not sure about changing an overload protection - seems unwise - but 4 amps for a 4.3amp motor is a bit close. If it happens with the new pump, will do so.

Err, mercury (Hg) switches are not banned - they are readily available and commonly used. It is preferable to use alternatives to Hg because of heavy metal contamination on disposal (Minamata Disease, Japan 1956).

Liquid switches in an inert gas have huge advantages (eg in explosive atmospheres; no corrosion or erosion of the contacts; etc). And sometimes the term mercury covers non-Hg, conducting liquids. For what it is worth, my experience with float switches is avoid reed/magnet and microswitches if you want 15 to 20 years untroubled use. Rolling ball types come in Hg and microswitch variants and do work, often well.

Anyway, many thanks for the pointers.

 

[breezer]

show me where to get a mecury float switch then please.

I agree with you, micoswitch ones do wear out, but they have been banned, which is why i still want one so a link to some one selling them will be fab

 

[GilesA]

Well Google throws up this lot for float switches but for electronics, there are many more Hg switch manufacturers:

1) http://www.russell-scientific.co.uk/mercury_switches/automatic_float_switches.html

2)
http://www.assemtech.co.uk/productpages/float_switches_uk.asp

3)
http://www.pepperl-fuchs.com/pa/levcon/point-level-con/03720/index3_e.html

4)
http://www.grouproland.com/products.htm

No 4, Roland of Wickam Market, Woodbridge was the manufacturer of the one I bought 15 months ago but they seem to have grown a bit since then - their float switches are attic tank types like 1) above based on the Stuart Turner type which has gone over to microswitches - and which are wholly unreliable as the contact force is minimal - http://www.stuart-turner.co.uk/Default.aspx?page=429 - we had to change to the Roland and have stuck with them.

 

[uselessFCUK]

4A overload setting is undersized, as you've agreed, correct to 4.3A

Is there any couplers between switchgear and pump... isolator, plug/socket, JB ?

Could it be that the float switch is bobbing about causing chattering of contactor at/near low water level?

All connections secure?

All 3 poles of contactor at negligable resistance when closed?

I can't quite make out from your image if the pump current passes through all three poles of the contactor overload as in diagram above... I'm sure it does.


Mercury switches - are these just banned in automotive applications?


Regards
uselessfcuk