External floodlight

[anobium]

Started to change old light for new and what should have been hours job as turned into a nightmare .Existing cable has what appears to be 2 earths and a live and a neutral which were connected to old fitting. I crimped the 2 earths and connected to new fitting and switched power back on and the rcd tripped. Thinking maybe I had put wires in wrongly I dismantled and checked. No, wires ok, but I noticed an additional black wire in the cable which had not been used in the old fitting. I then found a nearby fused switch which was for a overhead fan had stopped working and the fuse had blown. In addition another nearby fuse which is on the outside line circuit had also blown. Replaced fuses, rewired outside fitting incorporating the black cable with existing neutral and switched on again. Bang, rcd tripped. I have in the past fitted/replaced several external lights and never had this problem. Also should say that there is an in line external junction box with a pir on the same cable a couple of meters away. Is it possible that this is the cause of the problem and if so should I just replace this with a new junction box. We don’t need the second pir. Any advice greatly appreciated.

 

[Adam_151]

How was the previous fitting connected?

 

[anobium]

Straight foward choc block in back of old fitting.

 

[terryplumb]

Show pics of the "Rcd" that trips ,and the wiring at the floodlight.
Had the old light stopped working ??

 

[anobium]

Sorry I should have said consumer unit tripping, old light never worked. My sons house and he only moved in about 6 months ago. On second thoughts maybe old light was OK and it was just a blown fuse. Cable to light is round white 5 inserts

 

[koontz]

I am the house owner, my dad started this thread here are some pictures hope they will be of some help.

 

[terryplumb]

Thanks for pics. I assume the floodlight on the bench is the old one ?
It is the wiring at the new light fitting that we need sight of.
The consumer units RCD is the wide one in the middle of the board ,please confirm that tripped. To the left of it ,is
an MCB in the " off" position , what circuit does that protect ?
Do you have any electrical test equipment ,such as a multimeter ?

 

[koontz]

Yes the floodlight on the bench is the old one, do you mean you head to see the back of the new floodlight?, Can't do that right now as it is installed on wall but it's basically a round fitting with 3 holes for live, neutral, and ground. The off switch is just for the immersion heater, when it tripped it tripped the socket switch. Do have multimeter but not to sure how to use it

 

[terryplumb]

So it was not the Rcd that tripped as dad said ,but an MCB protecting a socket circuit ?
Yes ,need to see wiring at the outside light. Dad said the cable has 5 cores. Need to know what he has done with them !

 

[koontz]

Sorry not sure what mcb is?, The consumer unit tripped twice and both times it was the socket switch that tripped, have replaced fuses in both those sockets but now I don't get anything, the socket with the switch controls a fan/light in conservatory, and we are presuming the fused socket below that is to do with outside light. After the 2 trips we did change the connection into the new floodlight by putting the other black connection that wasn't in use on the old floodlight into the neutral in the back of the floodlight. So now the fan/light in conservatory doesn't work and nothing trips or works on those switches.

 

[terryplumb]

The MCB's ( miniature circuit breakers) are in your consumer unit ,and each one protects a specific circuit , like the one for your immersion heater. And each of the others ,for instance ,socket circuits ,lighting circuits etc etc.
They trip when excessive current runs in the circuit.
The RCD is to the right of your immersion MCB ,and it protects against earth leakage on those circuits connected to it.
So ,as I understand it ,your MCB on a socket circuit is what trips and NOT the RCD. Is that correct ???

 

[koontz]

Yes it did, but now I get nothing, also when I connected it up I turned all the switches on the consumer unit off including the rcd.

 

[terryplumb]

Are the sockets on the circuit also not working ?
I assume the MCB has been switched back on.

 

[koontz]

All sockets are working mcb is switched on.

 

[terryplumb]

I suspect dad has created a dead short ( short circuit) in the wiring at the outside light.