Bedside lights trip rcd

[m4tty]

Hi,

Changed a board Thursday and all went ok. Got a phone call today saying the bedside lights are tripping the rcd when switched on.

I'm going there in morning to sort it out. Either borrowed neutral from another circuit or short to earth. They must be spurred off the ring as lighting circuits are not earthed all class 2 and I didn't forget the sticker on board and note on certs

I always get worried that what if I can't sort the problem, low in confidence I am.

Any thoughts on quickest way to go forward?

Cheers

 

[steptoe]

are they plugged in bedside lights?

if not chances are switch from lights,

neutral from sockets, with them being low level.

 

[Badger]

Hi,Changed a board Thursday and all went ok. Got a phone call today saying the bedside lights are tripping the rcd when switched on.

I'm going there in morning to sort it out. Either borrowed neutral from another circuit or short to earth. They must be spurred off the ring as lighting circuits are not earthed all class 2 and I didn't forget the sticker on board and note on certs

I always get worried that what if I can't sort the problem, low in confidence I am.

Any thoughts on quickest way to go forward?

Cheers

did you megger the circuits at 500v and if so id anything show?

 

[Evans Electric]

You'll sort it M4tty , you already know its the wall lights so you're half way there .

As Steps says , and if theres no earth on the lighting , they probably come from the ring . If its a DIY job it may be just a load of carp , or something simple like a fixing screw into the neutral .

Have confidence , you'll find it .

 

[batty]

As Declan says you are half way there knowing whats causing it Matty you'll get it sorted.

 

[m4tty]

did you megger the circuits at 500v and if so id anything show?

I meggered the circuits at 500v but missed turning this switch on

---------- Post Auto-Merged at 22:27 ---------- Previous post was made at 22:25 ----------

Thanks guys much appreciated they are from the socket circuit but I didnt see an fcu so am a bit worried they've been wired straight from the ring ffs. Hope not!

 

[batty]

Seen that a few times Matty got some pics of a clock outlet wired of ring will have to post that some time.

 

[steptoe]

at worst then m4tty its only a short cable, so maybe even a dodgy connection at back of fitting if your lucky.

 

[Doc Hudson]

13a plug wired wrong?

Doc H

 

[m4tty]

Its hard wired doc not plugged in

 

[m4tty]

Got there this morning and had a look. Not a borrowed neutral as upstairs sockets on same side as upstairs lighting. Found the junction box in loft which it's fed from and it's fed from upstairs lighting circuit which has no earth. Dunno If im being thick here but i Can't really work out how rcd is tripping if there's no earth. Prob missing something basic here so feel free to shoot me down.

The customer said he had problems when installing these light and his uncles brother in laws dad sorted it out for him lol. Think that one of the cables were drilled through when installed few years back.

Why the rcd trip with no earth tho?

Sorry if I'm missing something basic here

Cheers

 

[Apache]

Matty - you don't need a functional earth to trip the RCD. Remember they have a coil that is balanced so if current is going anywhere (through a person, through a nail to the general mass of earth) the coil will be unbalanced and the RCD will trip. Remember that an RCD has no earth connection!

 

[m4tty]

I know what your saying and definitely understand about an earth not needed as current flow through a person touching the live or neutral but I can't see a screw through the cable actually getting to true earth? That's where I'm stuck. Where would the current be flowing to imbalance the rcd ?

Cheers for the reply mate

 

[Apache]

I can't see a screw through the cable actually getting to true earth? That's where I'm stuck. Where would the current be flowing to imbalance the rcd ?

Matty, give this a little thought. Assume you are completely 100% insulated from the ground - up a yellow fibreglass ladder. You can grab a live wire and nothing will happen. You agree? The reason is that the electricity cannot flow to the general mass of earth. If you grab a live conductor stood in the sitting room in your shoes and on carpet you will get a bit of a shock. If you do the same wet and naked in the bathroom you get a bigger shock. The current is flowing from the live conductor to the general mass of earth.

This is distinctly different to the MET that all the earth cables (cpc) are attached to. The idea is that the 'MET' has a lower resistance than the flow to the general mass of earth. Electricity will always flow in the path of least resistance. The idea (therefore) is that should a fault cause your metal walled kettle to become live (assume no RCD for simplicity) then the kettle will be connected to earth and the current will flow preferentially to earth rather than through you to the general mass of earth. This is why extraneous metal work was bonded, so that it was at the same electrical potential as the MET. (remember for current to flow there has to be a potential difference)

A nail touching a live conductor may or may not cause the RCD to trip. It would depend on the ability of the substrate to conduct electricity to earth. A wall that gets damp and then dries out can cause intermittent tripping.

Does that help? I am a little confused by your term 'true earth' - whether you mean the general mass of earth or the MET.

 

[m4tty]

Thanks for taking the time patch to help me on this one. I understand everything you said above but would have thought the met would be at earth potential.

I can't get my head round the fact that it was screwed through plasterboard and maybe some wood. But there is no chance this is damp as immersion heater was in cupboard in corner and sweat was dripping from me. So I cant see a path to earth. It was tripping instantly when turned on so I think a wiring fault is more likely. Which I wish I had delved into more but they said just disconnect as they weren't bothered about them.

It's one of them that's going to annoy me until I can find out some possibilities of the cause.

Thanks again patch

Cheers

 

[Evans Electric]

I know the feeling Matty , OK lights are isolated , but what the hell was the problem !!!

Were they Class1 fittings .

Although its sorted now I suppose , just wondered if you meggered the cable drops down the sheathing , sheathing nail spiking a conductor , who knows .

 

[m4tty]

They were class 1 and I know I missed it which I shouldn't didn't get chance to test further as they said just disconnect. Their minds were made up and they were happy at end of day so like you say ... Who knows cos I dont lol

 

[Evans Electric]

Oh well , put it aside and move on .

 

[Lee321]

matt other items may have brought your leakage to 29ma and no rcd trip. when your lamp is switched on and a squashed cable etc is leaking it need only be 1ma