Testing Consumer Unit, Now Switch Keeps Tripping!

[Rsian]

OK.

My mistake, it says out door lights NOT greenhouse (greenhouse is the rcd next to this one).

See picture below:

The shed CU goes back to the house CU. There is an outdoor box with an unterminated cable cable going to it which looks like it goes back to the shed CU from the direction it starts to go in, but can't tell for definite as it goes under ground.

The pump is where the pump is.

In the front room there is a six switch wall switch which controls a floodlight, some decorative lights, the pond pump...and the other three I don't know what else.

Everything has been working perfectly up until now.

I did switch the pond pump on and off a couple of times from the three way, and it was around this time that it wouldn't come back on.

In the morning, how should I best eliminate the pond pump - when I say I have powered it off, I have switched it off from the 6 way in the front room?

Should I then reconnect the neutrals one by one as the second option?

 

[333rocky333]

Power down the 3 mcb box and fish out the neutral terminal in the top.

Theres a lot of bare copper exposed in there, no disrespect but I would question someones competency first before they"fish" around in there

 

[Rsian]

OK.
So I have, as far as I can tell, killed all power to the pond pump, and still the RCD is tripping.
I'm not sure exactly how the previous owner has wired the switch in the front room to switch the pump on and off, maybe this is wired into the RCD in the shed which houses the house CU?
Could this be causing the problem?

 

[bernardgreen]

So I have, as far as I can tell, killed all power to the pond pump, and still the RCD is tripping.

Disconnecting or switching off the Live to an appliance will kill all power to the appliance but if the Neutral is still connected then a fault between Neutral and Earth or between Live ( at the appliance) and Earth can trip the RCD if power is being used else where.

 

[Rsian]

I am not a qualified electrician (you may have guessed), but am competent enough to do some basic fault finding, and would never undertake anything deemed unsafe. I need to get my shed demolished today, but obviously need to be satisfied power has been killed to the shed (which I am certain is has), but also would like to determine where this fault has occurred (as it still could have happened at the shed end I guess).
Happy to trip the house CU switch to kill all power if need be - is there some definitive fault finding I can do to the the 3 MCB, as it appears the fault is lying between the RCD in the house CU and this MCB?

Pic attached of what looks like the external water pump socket. The loose socket on the bench has always just hung loose, the socket which is plugged in I have disconnected and still the RCD trips.

 

[ban-all-sheds]

Damn, apparently this didn't post about an hour ago:

The little 3-way wylex that has the shed and pond pump in it - what does the middle MCB control? The fault could be on this circuit and you're missing it by only assuming it's the shed/pump.

It's a neutral-earth fault if it won't reset with the MCBs off.

Yes, but...

Yes, but...

The OP has not done anything to any wiring, cables, connections or loads.

All he has done is turned breakers on and off.

 

[Iggifer]

No (s)he hasn't. But coincidences do happen.

It could be that the RCBO has died and no matter what he does he won't be able to resolve it.

 

[Rsian]

Pond still without pump.
Any advice on how I can test would be appreciated.

There is an RCD on the house CU next to the tripping one which is not in use - am I able to make use of this for testing purposes?

 

[333rocky333]

As informed earlier, for each of the 3 reds there is likely a corresponding black, either passing through into the main cu or most likely in the 3way box.
there will be the incoming red from the tripped rcd connected to the bottom of the 3 mcbs, and the black incoming , possibly in that connecter block in the 3 way box, therefore 1 black in and 3 blacks out.
if you find the corresponding pairs, proberly the same size as the red, or exiting the same conduit, then you can connect 1 circuit at a time

THOUGH YOU NEED TO ENSURE THE 3 WAY BOX IS TOTALLY DEAD BEFORE POKING INSIDE DO YOU HAVE ANYTHING TO TEST

 

[Rsian]

As informed earlier, for each of the 3 reds there is likely a corresponding black, either passing through into the main cu or most likely in the 3way box.
there will be the incoming red from the tripped rcd connected to the bottom of the 3 mcbs, and the black incoming , possibly in that connecter block in the 3 way box, therefore 1 black in and 3 blacks out.
if you find the corresponding pairs, proberly the same size as the red, or exiting the same conduit, then you can connect 1 circuit at a time

THOUGH YOU NEED TO ENSURE THE 3 WAY BOX IS TOTALLY DEAD BEFORE POKING INSIDE DO YOU HAVE ANYTHING TO TEST

Will a DVM suffice to test if it is live?

 

[Taylortwocities]

Will a DVM suffice to test if it is live?

Yes, but follow the safe isolation procedures detailed here
//www.diynot.com/diy/threads/electrics-safety.7553/

this will help you make sure that
1. your DVM is working and set to the correct range
2. that there is power there before you switch off
3. that power has been disconnected after you have switched off

 

[Rsian]

Will a DVM suffice to test if it is live?

Yes, but follow the safe isolation procedures detailed here
//www.diynot.com/diy/threads/electrics-safety.7553/

this will help you make sure that
1. your DVM is working and set to the correct range
2. that there is power there before you switch off
3. that power has been disconnected after you have switched off

Thanks Taylortwocities.
I can't get access to my Fluke DVM until next week, was going to pick up a basic one from Screwfix >>> http://www.screwfix.com/p/lap-mas830b-digital-multimeter-600v/75337

LAP MAS830B Digital Multimeter 600V

Would this suffice for my purposes?

 

[Taylortwocities]

Any multimeter wil be fine.

Personally I would go for a purpose tester like this
http://www.screwfix.com/p/fluke-t90-voltage-tester/7027j

But then that's something for using when you are doing electrical stuff every day.

 

[Rsian]

Cool. I'll pick the LAP one up for now this evening, maybe look at the Fluke one another day.