Odd one with RCBO trip

[ssizen]

Hi all
Some advice, thoughts, ideas sought please. Recent install in our house, seperate CU for outside supplies (some SWA feeds to garage, etc), one circuit is a 6A RCBO to run quite a large pond pump, this was tripping the old CU main RCB but that was located to water in the connector for the pump cable into the SWA that feeds it, that was fixed. Now the pump runs for about 5 mins then trips, there is no reading of any short at all between Live / Neutral and Earth before or immediatly after the trip, the multimeter shows an open circuit.
Any ideas? Could it be shorting with load? Or maybe the 6A is not large enough? The pump is a submersible but quite hard to get at so it will not be easy to lift that and check / determine the rating, will have to of course if it cannot be resolved but thought best ask the group first
Cheers
shaun

 

[sjm]

I would suggest overcurrent to be the problem. Put your clamp meter on it and check. If the pump is old or sticking it could be drawing to much current.

 

[telectrix]

what are you testing with, multimeter or MFT?

 

[nickblake]

What could well have happened when the water got into the connector some of the water ran through the cable into the pump this could then cause the RCD to trip in the way you have described , sure you'll find water in the pump , it could well be over load like SJM has said so could be worth checking both let us know

 

[ssizen]

Hi
Checking at present with a multimeter, will check the current load, the pump is about 3 years old now, was I recall a good one (staurt Turner), would not think the water has got down the wire, the connector was only damp (and showed some rust / arcing on the screw connector) but the cable from there to the pump is about 20m so a long way to filter down (mind we all know how good water is at finding a gap!!).
Will check current draw next, oddly though I would have thought it would spike at start up of the pump then settle when it runs but as you say if its clogged / old then the laod may build I guess
Cheers

 

[telectrix]

multimeter is no use. you need to test at 500V with an insulation tester. short L-N and test to E. if that's OK ( > 2 Meg. ) then measure current as suggested.

 

[Strima]

My moneys on a pump full of sludge. Clear before running, sucks up some crap, overheats (yes it can happen underwater) then the crap falls out again when the pump throws a wobbly.

 

[Octopus]

Agree ^^^^^ 110%

Seen it recently, loads of muck in the pump/pool and on the previous occassion it turned out to be a worn motor, heating up and seizing!

 

[ssizen]

Yep fair points, time for a wade, trouble is its 8ft deep at that part!!! seemed like a good place when the pond was empty!!
Will let you know how the scuba exploits go, thanks for all the advice
Shaun

 

[ssizen]

As it turns out the pump was full of water, amazed it worked at all, well damp if not full, it seems to have a oil chamber at the bottom which they say is the most relaible seal you can get, not really yhr case and it was a very expensive pump
Now I have to see if I can get the parts to fix it..Thanks for all your help

 

[Strima]

Cool, let us know if you fix it or sling it!!!