RCD Tripping -any suggestions

[ETAF]

had a RCD trip today.
When my wife Switched OFF the en-suite Main light.
More detail later on what I have tested and tried.
MCB's are Not tripping
Isolated the fault down to the bathroom/ensuite Lighting circuit. I removed the Live and Neutral at the consumer Unit. With this circuit disconnected every thing else on that RCD group is now working

Recent new installation.

New Consumer Unit fitted around Oct 2018
All Light units (Bathroom specific spec IP rating) NEW and ALL NEW Wiring in April 2019
By Electrician and Signed off , along with a lot of other work.

ONE question is
RCD tripping but not MCB indicates a neutral to Earth fault - is that correct
testing cable etc - I do not have a mega testing, only a Multimeter, so may not be able to isolate with testing

The faulty circuit provides
All Lights Bathroom / IP rated for zones etc
Centre Light in Bathroom , I have disconnected - still trips
Centre Light in Ensuite , I have disconnected - still trips
Wall /mirror Light in Ensuite, I have disconnected - still trips
Checked loft JB for water , damp etc - all fine

I have NOT yet checked
Shaver Socket
Bathroom LED lights
Any of the Switches - 3 Pull cords - 2 in ceiling and 1 2A architrave for LEDS

ALL the lighting cables runs via 1 off 20A JB in loft , about 6 T&E cables - going in
I took the top of JB off and moved all the cable around, - (I had an issue before with this Electrician and a JB poor quality Job, insulation split and shorted out, also A Double Socket Screw trapping Live and intermittent shorting live, MCB tripping - Now have a new electrician for rest of house rewire/work)

SO before I disconnect ALL these cable and test one by one with the RCD - I will try a multimeter, in case its a short, which the multimeter can detect.
BUT as i say i do not have a MEGA tester , NOT sure if i can get a cheap one

Any suggestions before i spending most of the day tomorrow in the loft removing all the cables from JB and then testing each circuit individually by checking the RCD trip and then hopefully fixing whatever is faulty.

Nothing happened / changed today , raining , but loft is dry in that area

the fault occured when the Ensuite Main light was switched OFF via the plastic ceiling pull cord
I have not checked the plastic ceiling mounted Pull cord switch , but i have completely removed the centre light, as mentioned.

Not sure if a switch can case this issue , as MCB is OK, JUST RCB , which i thought indicated a Neutral to Earth fault.

Thanks

 

[blup]

You can test the physical connections in the switch for tightness etc.

If that doesn't identify the problem, it's appropriate to get an electrician in.

Blup

 

[ericmark]

The Mega tester (insulation tester) cost around £35 for one not calibrated, which is fine for DIY.

The MCB if switched off as you say only switches off the line, so anything with a neutral fault will still trip the RCD.

Neutral and earth with no load in a TN installation are the same voltage, only as you put a load on it does the voltage between the two vary, so it can be misleading where it seems some thing big causes the tripping.

However 30 mA at say 5 volt (difference between neutral and earth) is 166 Ω and at that a multi meter may detect it, it is worth a try. In the main we take a stab at likely cause, outside light is first on list.

 

[ericmark]

This one seems cheap enough but how long it would take to get it

This is where you start thinking outside the box, and I have not thought of any way to safely test without a proper tester, as they use 250/500/1000 volt but the current is limited, any other device does not limit the current, so question is if simpler to get some one who already has one.

 

[ETAF]

thanks for the replies

I had looked on amazon, but saw a few bad reviews, will look at the one posted - worth having in the toolbox
As you say of takes a while , i may spend the day redoing the JB - Just thought i would check here if i missed the obvious

Yep, suspected outside light , we do still have 1 old one , which has not yet been changed - BUT none on that circuit , as I have physically disconnected the T&E live/neutral for the lighting circuit and its stopped tripping. The earth is still connected - JUST the L & N at the CU for the one lighting circuit removed

Everything else in the house is now working, including all items on that RCD group, with just the one lighting Neutral & live T&E removed
All outside lights are working OK, which I suspected & also something plugged in the bedroom ring on that RCD Group - so removed everything from the sockets - Fixed an issue at my son-in-laws - intermittent tripping due to a hairdryer plugged in
I removed everything off the ring main , etc etc, and isolated where I knew Live/Neutral Spur - Only have1 , before I opened the CU

Now everything else is working so i'm only left with the items listed.

I'm left with a Shaver adapter and 3 pull cord switches

 

[ETAF]

When I was a computer Engineer (old days when you needed an engineer), I was supplied with a NICE set of test equipment , all FLUKE multimeter & Mega tester, plus oscilloscope .
I also had purchased a nice AVO8 back in the 70's when I was electrical / electronic training. All gone now, just have a cheap Multimeter

Feb timescale on that Mega, oh well may be doing it the hardway

 

[ericmark]

Now I know why I went all RCBO. My Mega went missing so I got this one

Of course as soon as it arrived found the Mega, so compared results and near enough the same, only down side is no continuity range.

Yes also have an AVO Mk8, good decoration, but never use it.

P.S. just noted both have same number VC60B+ putting that into google gets loads of hits. Found a review here seems both versions work OK.

 

[ETAF]

thanks for the info on the mega. good to know its OK for a DIYer - I may look at investing in that one.
AVO8 mines in a garage and has not been used since 1982 when i picked up/issued all the FLUKE gear , when that all handed back in 1990 I just got a small cheap multimeter

 

[333rocky333]

RCD tripping but not MCB indicates a neutral to Earth fault - is that correct

I am sure a L To E fault can often trip an Rcd without the Mcb, that fault can often be traced to a circuit via isolating individual Mcbs.
It basically takes 30ma to trip the Rcd, far less than to trip an Mcb.

Neutral to Earth faults can also trip Rcds, often with out an Mcb going off, these are harder to find, as The source current tripping the Rcd can be from ANY of the attached circuits and not necessarily the Circuit with the actual N to E fault, from experience i have often found N to E faults on lighting circuits have not tripped Rcds till Higher load circuits like cookers etc, are in use.

Only xmas was called to a house with a main Rcd going off when cooker was in use, told all started when so called electrician put up a pendant, when checked he had screwed through the twin and earth, shorting N to E, however the lights all worked fine as said, till the cooker was turned on. the customer was all prepared to bin the cooker and miss there xmas dinner.

My initial test, if no sensitive loads, is to do a global test of the circuits fom the Db and if low readings start disconnecting relevant circuits[/QUOTE][/QUOTE]

 

[ETAF]

thanks very much for the reply & information

My initial test, if no sensitive loads, is to do a global test of the circuits fom the Db and if low readings start disconnecting relevant circuits

I have removed/disconnected the one T&E for the Lighting Circuit in bathroom/en-suite which I has specifically asked to be installed on its own MCB circuit, removing the Live & neutral at the CU and everything else connected

The source current tripping the Rcd can be from ANY of the attached circuits and not necessarily the Circuit with the actual N to E fault,

everything else is now working fine. all lights, few things on Ring main & oven , only things on the Group RCD

That 1 T&E goes from the CU to a JB , and then that JB has cables for the
Bathroom Main Light - fully disconnected the light - LN&E, - controlled from a pull switch -
Bathroom Mirror LEDs on transformer - controlled from a pull switch -
Bathroom Shaver adapter, no switch, never really used, nothing plugged into it
En-Suite Main Light , - fully disconnected the light - LN&E - controlled from a pull switch
En-Suite Mirror light, - fully disconnected the light - LN&E - with built in pull switch

nothing changed

 

[bernardgreen]

that fault can often be traced to a circuit via isolating individual Mcbs.

Often but not always. The RCD trip can occur when the MCB for the circuit with the N-E fault is switched OFF

 

[ETAF]

thanks very much for the drawing - edited showing where I'm breaking the circuit to solve the RCD tripping.
So it must be in that circuit as the Earth is still connected up - But cannot return on neutral as disconnected OR Live , as you mention some issues.

 

[blup]

There are some cheap(ish) calibrated combined continuity and insulation resistance testers on ebay atm. Might be worth a punt.

Megger MIT230 Insulation and Continuity Tester NEW CALABRATION CERT | eBay

Blup

 

[ETAF]

thanks for ebay links, I will probably disconnect ALL the JB and slowly add until the RCD trips again
Will be slow as in LOFT
Normally I would do a half/half test - BUT the JB is so full , so will take my time document each connection, as it looks like the 4th terminal is being used for a return switch - BUT no brown sleeve on the BLUE return cable, (really unimpressed with this sparky , and why i wanted his work separate from the one who installed the CU and rewire - BUT this guy was part of the team that installed the kitchen & bathroom) - and i think i may break the JB out into 2 and fully label. I have cable 1mm/1.5mm anyway.

 

[333rocky333]

Often but not always. The RCD trip can occur when the MCB for the circuit with the N-E fault is switched OFF

View attachment 218813

Yes true for a N to E fault.
But the bit you quoted was relating to LIVE to E faults, which the OP believes he may not have due to the Mcb not tripping