Problems with garden elec circuit RCD

doctored

Can anyone help me on this?
We recently had an outside mains socket installed, plus wired into a 12V transformer for outside lighting circuit.
It is all off an RCD in the kitchen, which now (started over last few days) keeps tripping within a minute or so of being turned on. Worked fine for last few months.
We have had some problems with water getting into some of the 12V lights recently, but I have just disconnected EVERYTHING from the circuit, including the outside transformer, and it still trips.
Does this mean something horrid has happened to the outside cable? Or could it be the RCD itself that is at fault?
The outside cable has a woven metallic 'sheath' (under the outer clear plastic layer), I'm guessing to protect it from spades etc. This isn't actually earthed is it - just a physical protection...?
I wasn't exactly impressed with the guy who did the work - have a receipt from him. So last question - can anyone let me know which accreditation I should check/ask to see so I know it is a bona fide installation?
Much thanks for any replies...

flang

The cable will prob be SWA (steel wired armor) where the armor is usually used as the earth.
It would be unusal to get a fault in swa cable however there is a chance that water could be getting in as the end.
Have you tried wiring say a light into the RCD to see if it still trips?

Cypher

The cable sounds more like SY Steel Wire Braid Cable



Its more flexible than a SWA and has a clear outer plastic cover.

Flexible Armoured SY Type Mains Cable

A continental style flexible mains cable, commonly known as ’SY’ type, which has three layers of protection, combining the characteristics of a flexible mains cable with that of a steel wire armoured type. It is ideal for applications where power is required in arduous situations, on automated or robotic equipment and where equipment may be subjected to vibration or movement. The method of construction and materials used provide a high degree of flexibility and mechanical strength, coupled with good resistance to a wide range of chemicals. The braid provides partial electrical screening and the cores are colour coded or numeric coded for identification.

flang

Yeah your right reading that again it would make sense!!!!
Ive never liked that stuff!!!

doctored

Thanks - it is armoured cable, but only one 'layer'. Also it isn't earthed at either end in the outside circuit - only the internal earth cable is wired in.
I have disconnected EVERYTHING from the RCD - so there is just power going 'in' and nothing on the 'out' side at all. It still trips within a few seconds of being switched on, so this must be a fault with the unit itself??

The guy who did the installation (was recommended by the guy who did the garden work) has mounted the outside switch (turns on power to the 12V light circuit) on a wooden sleeper. When I checked yesterday this had a LOT of condensation inside it, which was what I thought was causing the problem, but it seems to persist even with circuit disconnected.
Anyway, gonna buy a new RCD today and give that a try with nothing connected at all. If that still trips presumably we just have a poltergeist...

roger56

Your "electrician" should have tested the work and provided at least a minor works certificate as the work carried out is notifiable.
I suspect the condensation may be causing enough leakage to operate the RCD (and the RCD is probably doing exactly what it was designed to do - protect against fault currents). The "electrician" should have tested the RCD to prove it works (for your safety along with other tests). It is also a requirement of him installing the circuit in the garden.

Electrical installations and modifications (with very very limited exception) are notifiable under the building regulations and must be carried out by a "competant person" ie someone who has passed "Part P" certification.
"You" are responsible for this, failure to comply is now a criminal offence.
Read this guide to be aware:
http://www.niceic.org.uk/downloads/Pocket%20Guide%208.pdf

doctored

Many thanks for that.
I have replaced the RCD device completely, and it seems to have stopped tripping - so I can only guess that the condensation in the switchbox I found was a coincidence - but still not nice!
Was not at all happy with the standard of the work this guy did for us, although he did give a printed receipt detailing the work done. Can't see any evidence of any formal qualification on this though. Is there anything equivalent to the CORGI mark I should be looking for?
Thanks.