I have a nightmare problem, can anyone help?

Whilst everyone was asleep this morning all of the power went off...

The main trip just after the meter (I assume some sort of RCD) had tripped....

After process of elimination I can prove that the lighting circuit (only one lighting for the entire house), is causing the problem.

If I pull the lighting fuse out of the box, the power to the rest of the house works perfectly without tripping the RCD.

The weird thing is, I can put the lighting fuse back in and switch on the house RCD, everything comes back on including the lights, for about 6-10 mins, and then pop the main RCD trip thing goes off again...

I have run around the entire house in that 6-10 mins turning on every single light one at a time to see if one of the lighting systems has a fault on it... but all of the lights seem to work...

So why is the lighting circuit tripping the RCD and not blowing the fuse? (5A)


Any suggestions of what to try next? I could admit defeat and call in some help, but I would rather not have to!


The house is 1900ish, appears to have been wired badly, some rubber, some plastic, cables with odd colours... I fear a massive short somewhere under the floors.... we had new carpets fitted last month

[Edited on 2/12/09 by tegwin]

At a stab in the dark, could water be in the electrical circuit, as it has rained alot recently. An Rcd is designed to trip when current leaks to ground. The current flowing could just be below what is required to trip, then randomly increase above limit, then trip RCD.

Do you have dimmers, a fault could cause it to trip, if it is leaking to ground.

Check each switch for water (ideally with no power), looking for water flowing down the wires.

Next look at the light pendants for water.

Darren

[Edited on 2/12/09 by turbodisplay]

A short between live and earth is most likely causing your problem. This won't be bare wires touching but more likely water in a light fitting, a trapped cable in the back of a switch or just really old cable that is starting to break down.

Earth leakage is what trips the RCD... there would appear to be an intermittent fault somewhere in the circuit.

You'll need to get a leccy in with a megatester to trace which area has the fault (got any mice? They like lunching on the insulation)

Ironic signature in your posts there!

It's a bit odd for an intermitant fault to behave predictably.

Do you have any lights on timers or outside lights on PIRs. i.e. anything that swtiches automatically.

EL trips are generally set with a very low threshold and a very small or no delay - designed for personnel protection. Water is probable given recent weather, but if the interval from switch on to trip is repeatable at 6 - 10mins then you should for something that changes in that time, something that heats up or expands perhaps, something on a timer, central heating timer.....?

An RCD detects low level currents to earth 30 milliamperes to be exact.

All electrical equipment has some leakage to earth especially computers and cooker elements also transformers.

Do you have any low voltage downlights in the house a leaky transformer could be the culprit.

Sometimes it takes a wound component a few mins to warm up and start sweating before any trips go.

If it was a fault in the cabling (short) the circuit wouldn't be ok for a few minutes, I think it would go straight away.

Could also be extractor fan connected to lighting

u2u me mate and will try to help. live to earth fault would trip an mcb so i would imagine you either have a faulty appliance plugged in somewhere causing slight leakage then something else taking it over the rated m/a. or water in a fitting,(usually an outside light)
another problem we have been having lately at work is with earth faults on boilers, usually in pcb

Do you have a porch with a light? Quite common for them to cause this kind of problem.

You had a carpet fitted last month, perhaps they hit a cable. It has been known that the fitters secure loose floorboards before fitting the carpets, a nail could have pierced the outer sheathing and causing a short. I used to get called out often to gas leaks. Worth a check

Turn off all the lights and reset - If it stays on beyond 10 min then you likely have old wiring thats moving under the slight heat of the load and then shorting - any other immediate fault (e.g. nail, water) should trip out immediately...

Only other thought is you might have a dodgy flourescent bulb somewhere that's putting an equally dodgy spike on the system after it warms up?

You'll have to rewire at some point - If you ever want to sell your house then you need a certficate of testing now from an NICEIC registered electrician

quote:

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Originally posted by NeilPYou'll have to rewire at some point - If you ever want to sell your house then you need a certficate of testing now from an NICEIC registered electrician

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Liam,

Your right - I checked - not complusory but under the optional bit of the Homebuyers Information Pack the survey would include a by inspection check of electrics.

"General advice
Safety warning: Periodic inspection and testing of electrical installations is important to protect your home
from damage and to ensure the safety of the occupants. Guidance published by the Institute of Electrical
Engineers recommends that inspections and testing are undertaken at least every 10 years and on change
of occupancy. All electrical installation work undertaken after 1st January 2005 should be identified by an
Electrical Installation Certificate."

We moved just when this beastie was being agreed on and I could have sworn at the time they were going to make both electricity and gas safety inpections compulsory - maybe that was just for rented property...

quote:

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Originally posted by NeilP
Liam,

Your right - I checked - not complusory but under the optional bit of the Homebuyers Information Pack the survey would include a by inspection check of electrics.

"General advice
Safety warning: Periodic inspection and testing of electrical installations is important to protect your home
from damage and to ensure the safety of the occupants. Guidance published by the Institute of Electrical
Engineers recommends that inspections and testing are undertaken at least every 10 years and on change
of occupancy. All electrical installation work undertaken after 1st January 2005 should be identified by an
Electrical Installation Certificate."

We moved just when this beastie was being agreed on and I could have sworn at the time they were going to make both electricity and gas safety inpections compulsory - maybe that was just for rented property...

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a spark would firstly disconnect the light circuit from the board and test the insulation. He could then seperate individual runs and test lengths seperately, to see if its a general old cable problem or something specific.

If it trips with the lights all turned off it would suggest a neutral to earth fault somewhere, but i would agree that the long consistant delay does sound like something specific.

In the short term you could remove the lights off the RCD, but id hesitate to suggest that without also saying you need it testing and fixing properly.

quote:

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Originally posted by tegwin
Even if all of the lights are switched off... could a duff bulb cause the issue? Most of them are those evil energy saving jobbies...

[Edited on 2/12/09 by tegwin]

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quote:

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Originally posted by JoelP
a spark would firstly disconnect the light circuit from the board and test the insulation. He could then seperate individual runs and test lengths seperately, to see if its a general old cable problem or something specific.

If it trips with the lights all turned off it would suggest a neutral to earth fault somewhere, but i would agree that the long consistant delay does sound like something specific.

In the short term you could remove the lights off the RCD, but id hesitate to suggest that without also saying you need it testing and fixing properly.

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The RCD is between the meter and the consumer unit.. (consumer is a retro bakelite affair with ceramic wire fuses)

I am imagining the consumer unit is about 30 years old, with some of the cabling a fair bit older!


The consumer unit only has 1 5A fuse with 2 live cables heading off into the wall.. I guess one for 1st floor and one for ground floor, but in this house who knows!

How does a spark test the insulation?


If I knew the problem was consistant and fixed I would be confident at disconnecting each segment of the lighting ring and testing for shorts, but because it seems to need some heat or somesuch to trip... this method would not work...


Anyone care to scare me with how much an electrician would charge for fault finding?

I am scared to invite one into the house because I am sure they will want to re-wire and replace a lot of the circuits and hardware... (would make sence, but I dont want to have to destroy the house for the sake of it!)

[Edited on 2/12/09 by tegwin]

an electrical test meter has a mode where it applies 250v or 500v and measures resistance in mega Ohms. Current limited to 1mA for safety. My meter reads >1000 on a new circuit. Older ones will drop to single digits. 2MOhms is the fail point, though you could work out how low it would have to go to trip a 30mA RCD.

Seeing as there is a delay, it may be that all the circuits are borderline, and you could prolong their lives by seperating them onto two or more RCDs, thus giving you more space for earth leakage without compromising safety.

How many fuses are there all in?

There are 8 fuses in the Consumer board.

15A imersion
5A- Lights
5A Wall fire
5A wall fire
30A- Socket ring
30A socket Ring
30-Socket Ring
30A cooker (disconnected)


The issue is that the RCD is next to the meter in the porch, the consumer unit is about 10 meters away in the hall... I would have to remove the porch mounted RCD and fit a new split load consumer unit with two fuses for the lighting circuit....

But I would be very concerned as to why the origional setup wasnt working.... giving it more scope to get hot and potentially start a fire is not good news......


hmm... just looking at insulation/earth testing gear... £200 odd quid.... might be a worth while investment........

Usually the Lights are not through an RCD

quote:

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Originally posted by mad4x4
Usually the Lights are not through an RCD

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new ones too with the 17th edition, ANY cable buried in plaster must either be on an rcd or armoured well enough to protect from nails and drills.

Id only buy test equiptment if you intend to do the rewire yourself - which lets be honest, its going to need it one day. Would just need to notify building control, they may accept your certificates, or they may choose to test at their own expense.

quote:

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Originally posted by JoelP
Would just need to notify building control, they may accept your certificates, or they may choose to test at their own expense.

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quote:

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Originally posted by big-vee-twin
All electrical equipment has some leakage to earth especially computers and cooker elements also transformers.

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LOL! I'd like to see you try and pass off a full DIY rewire as 'replacing existing' to building control/a solicitor! You can replace damaged cabling for a single circuit only without notifying - ok I suppose you could find that every section of cable is damaged one after the other, but already pushing it I think . You certainly can't change the consumer unit, or any fittings in a kitchen or bathroom, to name a few other stumbling blocks.

Liam

Part P Exclusions. This is what you can legaly do without notification, rather than what you can get away with...

Another session last night with the multimeter and screwdrivers..

I disconnected both live wires for the lighting circuits from the consumer unit and measured the resistance between L and earth... I was expecting infinite resistance.. instead I get about 8Mega ohms... Is that normal?

I then connected the two lighting circuits in one at a time... the ground floor circuit works fine, the upstairs circuit trips the RCD instantly... so thats narrowed it down to one floor..

Doing a "live test" shows me that the doorbells and shaver sockets are also fed from the upstairs lighting radial.

I disconnected them all and it still blows.

I think the next stage is to remove all of the light switches and light fittings and do continuity and short circuit "logic" testing on all of the runs to try and narrow down the location of the fault...

I have, for testings sake sepperated the two lighting circuits into two seperate slots on the consumer unit instead of just one...

Even after the above, I am still reluctant to let a spark anywhere near my house.. I have never had any tradesman do a job that I could trust...charging as much as possible and taking as little care as possible...

I can understand why Part P was introduced... but its a crock of sh1t... some people with the qualifications and "experience" are worse electricians than my little sister!



[Edited on 4/12/09 by tegwin]

A proper IR tester challenges the circuit with 250 or 500V to really show any insulation problems up, whereas your multimeter does not (probably uses 5V for resistance measurement). If you were reading 8Meg with a multimeter test, you might read much lower with a proper tester. You can get incorrect readings if electronics are still connected - such as flourescent light fittings and extractor fans, so make sure these are disconnected. Neutral to earth and live to neutral should also be tested, but as said you can't really do a proper test with a multimeter anyway.

But keep plugging away and you may eventually find the fault! Good luck.

Liam

measure neutral to earth too, as NE faults will trip an RCD.

8 megs is getting poor but isnt bad enough to trip the rcd.

If you are concerned about damaging equiptment on the circuit (which is only really a risk at 500v) then you can hold live and neutral on one probe and the other on earth, which stops current flowing through circuits etc.