Thanks Chaps - follow up on RCD issues

[Dan delaMare-Lyon]

So - the whole lot went again at the weekend (Sunday of course) after nearly

2 months of working faultlessly. Sudden trip - no way to reset the RCD pretecting the whole lot (100mA).

Sparky was and still is on hols in Wales - and after a quick chat - I decided to work this thru on my own.

Popped the front off the fuse board and was amazed at the number of wires - bit daunting.

Started by dropping out the live of each circuit - seeing if there was any immediate change. No change - still can't re-set the RCD.

So start tracing back the neutrals from the bus bar to match up with the lives - the drop one circuit at a time - including dropping out of the equation and patching in with a long bridge all the works just done in the kitchen. Still no go - right up until I disconnect the last circuit - WATER HEATER - now the run to the boiler post all the works.

Back up it comes. Cue confused eyes.

Plug everything back in - except the boiler cct - plug all the applainces back in - re-create the circumstances under which it went - nothing - worked fine.

Cue curious eyes. Re-connect suspect circuit - RCD won't go live - hmmm - arse - it's the boiler - oh well - it's warm outside and I can get the telly back on in time to watch top gear and keep the beer in the fridge cold enough and avoid a mercy run to the folks with the contents of the freezer - result.

Stop and think about things - the boiler is protected by a fused DP switch - wonder what's going on - so disconnect the live and the neutral at the switch - and try again - huzzah - the RCD goes on. Odd.

Probably well against regulation (but I know it's a straight run - 1 join as far as the switch on 40a cable - I put a socket on the end and plug in a kettle and fire it up - figuring the boiler is 150w - the kettle is ~3kw - this should put a decent load on the cable and if it's screwed possibly cause it to dump - nowt.

carefully re-wire switch with boiler and cable meeting up. Reconnect all - check - double check - and fire it up - and all is fine!

So - either the boiler has an earth leak that's borderline enough to cause the RCD to drop out - or - there was a fault that I missed either in the fuse board or at the boiler end.

Either way - the electrician is going to come back next week to re-check the circuit - but it looks like either the switch is up the poke (unlikely) - or - the boiler is iffy.

Thanks for all the pointers you all offered before. Although I still don't have a definate finger of blame here - I am much better acquainted with it all - and reckon that if push came to shove I could replace the whole lot (fuse board) with a split load so that we could at least maintain some form of service if things were to go a bit awry. I know also know that we do have an earth provided by the leccy company - and our meter makes a really dodgy buzzing and popping/bouncing noise all the time - even when there's no load on it (which is a little annoying when you spend the afternoon with your head close to it - and is now more or less impossible to miss while sitting in the lounge) - so I'll call the leccy board about this.

So - progress (of sorts) - I'm quite chuffed. I did find lots of loose connections in the fuse board which can't be attributed to the sparky (not the ccts he played with) - and many of the neutrals were loose. That - and a bleedin great screw dropped out of the guts of the box once I got to connecting/disconnecting things - can't help but think a 6x1.5 woodscrew can't have been doing much good lost in the works!!

Thanks all once again, really appreciate it.

If it goes south again - think I'll get a megger (can you rent for a couple of days? I found a place selling them for a couple of hundred quid today - but that's a tad overkill) and test it top to bottom - and perhaps replace the fuse board...

On that topic - how do you do this without pulling the master fuse?? I know it can be done as I've seen it - but personally I don't like buggering about with something that's 100A @ 230v - and I can't get wellies in my size ;-)

Cheers Dan.

[John Rumm]

You can usually pick up a megger on ebay for £50... can always sell it again once done.

Pull the fuse - don't even think about doing it live!

[Stan]

Just a thought on that!

Here we don't use a fuse; after the outside meter (provided by the power utility but plugged into owners meter socket, the next thing is the main circuit breaker in its own separate section of the main panel (i.e. CU). So we have safely disconnected and then later reconnected (using rubber gloves for extra insurance) the overhead 120/230 volt incoming live leg/s wires leaving the neutral intact, by making sure everything in the house was switched off so that there was no 'current' flowing at all. We were also standing on a dry tar and gravel roof and the maximum voltage to ground being 120 volts RMS wearing rubber soled boots or shoes!

[Bob Eager]

quid plus VAT for a brand new one.

[meow2222]

You can make your own for a fiver. Use either a cockroft walton multiplier off the mains or a hand cranked microwave oven turntable motor to get the 500v / 1kV, and a standard meter or multimeter to read current.. Ether a 2nd meter to measure voltage or a zener & tr type arrangement.

But, meggers are dangerous items if you dont know exactly what youre doing with them. There are non-obvious electrocution scenarios.

And you dont normally need a megger to find a leakage fault anyway, in almost every case the fault shows up on a simple multimeter.

If you do replace the CU the boiler could go on the non-rcd side. Fixed earthed appliances really dont need rcd protection, earth leakage just isnt a signifcant safety issue with them.

NT

[Dan delaMare-Lyon]

Marvellous - thanks Bob. So the question becomes - which one do I need to test out all our cabling if my most recent works haven't solved it? I've seen loads! What I think I need to do is test each cct to identify a cct with issues - then chop up the cct until I find the fault. The devices plugged in end are a different challenge :)

Cheers Dan.

[Dan delaMare-Lyon]

Wouldn't have done - but haven't I read on here before that I'm not allowed to do this?

Cheers Dan.

[Dan delaMare-Lyon]

Sounds a bit heath-rob to me ;-) Cool tho.

Thus the looking for one - and then some learning :)

Gotcha.

Yup - everything would go on the non-rcd side that didn't need protection.

Cheers Dan.

[John Rumm]

Probably, since the fuse belongs to the supplier. Having said that people pull the fuse all the time when doing what you want to do, and no one seems to care. If anyone asked you could simply say "oh yeah, the chap who replaced the consumer unit did that!"

[Dave Plowman (News)]

A decent DVM will show up 99% of the faults a Megger will do.

[dmc]

Talking about "doing it live", I spotted people up loads of the pylons around here today painting them (yellow for some reason...)

Is this done live? Looks like the cables maybe earthed in the second shot so I guess not

[Dan delaMare-Lyon]

Just a quick follow up - Sparky phoned this evening to see how things were.

We had a chat - he has meggered the sockets cct. Cooker cct was untouched (as in no cable modifications - only past the switch) - and he only did R1+R2 on the water heater/boiler cct so will drop by and megger the circuit to work out what's going on. Failing that he's offered next time it goes south (if at all) to come and megger thru each cct until we get to the bottom of it. Although I think I could now do this myself - it's nice ot have someone to call on on a Sunday when it (inevitably) goes bang!

Again, huge thanks to one and all who offered advice - really have learned out of this. Now if screwfix would just stop sending sodding catalogues with bargain consumer unit bundles - I might be able to get the guts of the existing CU out of my head ;-)

Cheers Dan.

[Guy King]

The message from [e-mail] (dmc) contains these words:

[dmc]

Thought so. Still looked like a nightmare job though (made me feel guilty about whinging about having to paint the fence ;-))

Darren

[Chris Bacon]

I don't understand why they're being painted in the first place, unless it's for camouflage, or something.

[<me9]

Just one side, the other will be in service. they'll do one side then the other. The yellow is a primer/undercoat. Usually different colours are used for each coat so the supervisor can confirm that the contractors have applied a full coat each time.