Contactor/pump problem

[gordy71]

So i have been to look at a commercial heating system,2 boilers various pumps, actuators etc. 2 shunt pumps behind the the boilers manually operated from rotary switches back at the control panel. Pump 1 works fine, when pump 2 is switched on the contactor trips and trip neon comes on. Please bear with me as my experience with contactors relays etc is limited!

I only had an hour to look at the job last week and with no wiring diagrams struggled to see what was feeding what etc. Found which contactor was tripping, reset it and it went straight off again. However if you isolate power to the whole board then switch pump on it holds for maybe 10 seconds before going off again? The only test i did carry out was to check the windings of the pump. On the one that was working it came out at 200 ohms, the one that wasnt 80 ohms so i assumed it was a faulty pump due to the large difference in resistance. Plumber changed it and it still wont workWet Fish. I was reluctant to start doing IR tests until i could isolate individual wires but didnt have time. Will be going back friday to have another look and was hoping some of the you folk that are more clued up than me would be able to give me some things to look out for!? There is 230v into the feed side of the contactor, would it just be a case of faulty wiring from the board to pump? I hope so as i dont wanna make myself look like a lemon againray Thanks in advance.

 

[Bacon]

Is there an O/L fitted to these contactors for pumps?

Does pump trip contactor if off load?

Difference in reading may be down to age of individual pumps.

 

[Steve3948]

It could be pumping against a dead head, if the actuator has not opened, allowing water to flow, against a dead head it will overload.

Seeing as the pump has been replaced, can you open actuator or check it's opening, normally a bypass would prevent pumping against a closed valve.

Just a thought.

 

[Murphy]

run the pump, and put on your clamp meter see what it's drawing. Check what your o/l is set at.

Is their a capacitor on the pump? If this is faulty it could pull the load up as well. If there's a bearing away in the pump this could also increase the load Also. If its lifting the mcb the pump could be down to earth, the o/l could be faulty? Just a few suggestions

 

[Steve3948]

run the pump, and put on your clamp meter see what it's drawing. Check what your o/l is set at.Is their a capacitor on the pump? If this is faulty it could pull the load up as well. If there's a bearing away in the pump this could also increase the load Also. If its lifting the mcb the pump could be down to earth, the o/l could be faulty? Just a few suggestions

OP had the pump changed for a new pump, so unlikely to be bearings or capacitor :innocent