intermittant overall rcd fault

[lloyd1980]

Have got a problem guys and would appreciate some advice

was asked to do a mains change for an oap in his residential flat (privatly owned)
gave him 2 option price wise in regards to types of CU, gave him the cheaper overall rcd with mcb's option and more expensive straight board with individual RCBO's
explained at the time that the chaeper one can be a pain in the --- as it kills everything covered by the rcd (in this case 4 circuits as RCD other end covers the other 4)
he insisted on the cheaper option ( as they do )
installed it today started it at 9.30 and got the power back on through the new board by 12.30.
everything held and I was over the moon as seemed to be no faults.
held all afternoon
im clearing up at 5.30 and the think starts to go bananas, tripping constantly. old fella is stressing out as flat in darkness etc.
it started happening when they were starting to cook tea.
the board had tripped once in the afternoon but it seemed to be the chrome kettle doing it so the fella went and bought a new one.
now sometimes the cooker trips it, sometimes the microwave trips it, sometimes the toaster trips it
the fridge has never tripped it as been on all afternoon fine
I havnt tested the installation as doing this tomorrow morning
I tested the RCD's and on half x rated it didnt trip and on 1x rated it tripped 29ms
I did IR test across the board and the readings are very low as in between N - E 0.05 M ohms
and slightly higher on L - E
I havnt stripped each circuit down yet or had any fronts off as didnt have time
Ive left him telling him to only use one appliance at a time
its a mystery as the cooker is on seperate circuit to the flat ring
some of his lighting is wired in flex (diy job) but it only seems to trip when you switch on appliances

It did occur to me that it may be earth leakage as at the moment 4 circuits all go through 1 x 30ma RCD and the combination of the fridge the cooker and the kettle etc etc may be over 30 ma and taking it out
apart from moving the cooker onto the other rcd and testing the installation
what do you suggest I do????? apart from run for the hills

really appreciate the help guys and sorry for the long post
thanks

 

[Guest123]

Could be an accumulative leakage fault.

I would say RCD ramp test to check what the RCD is actually tripping at, if that checks out then I/R test on each circuit individually with everything unplugged, lamps out etc etc.

 

[lloyd1980]

ill do that first thing
I did think it could be accumalative leakage but i dont have a tester to measure it
just feel bad for him as the look on his face when i told him it could be a cable problem was a sight to behold, I could almost hear his wallets sinking feeling

just had a thought whilst having shower.......I should switch off really but I cant

If the ramp test turns out ok then its down to IR test

if there are no dead shorts between N+E on any ciruits can a low IR reading trip an RCD? I know this would suggest cable damage but its only a tiny flat.

I know the minimum acceptable reading for IR and accross the whole board it was well lower n-e was 0.05 ohms so almost a dead short

I just want to clarify so im not wasting time tomorrow

thanks

 

[5-Week-Wonder]

Rather than unplugging everything you could start doing I/R tests with Live + Neutral at equal potential and leave everything plugged in and turned on (but completely isolate the installation, obviously). It's a damnsight quicker and more reliable than trying to find and isolate/unplug everything... there's bound to be a damn neon messing up the test somewhere!

That might allow you to quickly narrow it down to a single circuit?

 

[Guest123]

Ramp it with all appliances unplugged firstly, then add one at a time to see if any one item seriously effects the mA value given by the tester. This will confirm/eliminate any one appliance but may prove the accumulative leakage effect.

Is there an attic above the flat??? any DIY been done recently???

Failing all that test each circuit L-E, N-E seperately to pinpoint the offending circuit and go from there, tracing out the circuit until you find the bad section af cable.

 

[bugsy]

don't take offence but are the n's all in the correct n bar

 

[lloyd1980]

it has to be n-e surley as if there was a l-e fault the rewirable would have blown beofre id worked there which it hadnt
it just doesnt seem to be one circuit tho as the cooker sets it off and so do the plugged in apliances seperatly at different times, sometimes it becomes stable and wont trip then other times it goes bananas.
as you can imagine this is just what i needed at half 5 with half my stuff back in the van and my tea on the table

I just hope they managed to cook their pizza without the flat going dead again in the dark. the poor old girl , she is frightened by electricity anyway and she looked like shed filled her pants when it kept tripping

don't take offence but are the n's all in the correct n bar

seriously?????

i normaly put the greens with the browns

 

[weller]

sounds like a earth to neutral fault, u shud learn from this experiance always test the installation before changing mains board exspecialy in older properties where u buy ur gear at???? TN robinson sell 5way amins board full rcbo as same price as an mcb duel rcd boars

 

[5-Week-Wonder]

don't take offence but are the n's all in the correct n bar

That's a good point... split board with dual RCDs?

 

[weller]

split load board is ok if u can fit it in to the place u are installing it seperate ur circuits as stated in 17th edition. only problem is u will end up with like 6 spare ways in flat that will prob never get used lol

also this might sound daft but beforeu change a mains board disconnec the tails from the meter and place an old rcd in to circuit the day before and see wheather it keeps in i have done it on older properties and it has saved my bacon many times, sounds stupid but for 5 mins of u time its nothing

 

[lloyd1980]

it is a duel rcd board and all the neutrals are in the correct bar

if this was the problem then as soon you used anything on the crossed neutrals circuit then it would go same as borrowed neutral syndrome on lighting as soon as light switched on - pop

the problem is intermitant and sometimes happens and sometimes doesnt
like you turn the hob on, it goes
reset board - try hob again , it holds, this time the microwave sets it off. re-set, try microwave again this time doesnt trip it
its intermitant and its never the same thing at the same time and sometimes not at all
like i said if crossed neutrals then would pop straight away as soon as something turned on, then would keep tripping everytime you tried it

I use a wholesaler that supplies me with a duel rcd board 8 way, including all mcbs for 50 + vat and otherwise its 20 + vat for the board and 11 quid an rcbo

so the price i pay is good, the board is good quality too to be fair

and the flat has 1 ring which includes the kitchen, the tv and other things were used all afternoon with no problem

the board is a split rcd, 4 circuits on 1 rcd
the only thing on the other rcd is the lighting

and the neutrals are definatly in the correct bar

 

[5-Week-Wonder]

What's the IR between L+N linked together and E?

 

[bugsy]

When you isolated the cooker was that at the ckr conn unit or MCB

 

[uksel]

have you tried disconnecting all other circuits except for the ring? if the appliances still trip the RCD at least you've narrowed it down to a single circuit.

also did you complete the 3 step test for the ring circuit, no spurring off the ringmain to feed some electric down the shed or some garden lights that might be creating a problem?

 

[WayneL]

My money is on a low IR N - E fault on your ring final.
The more you load it (eg cooker/ microwave) the higher the current
will be that's bypassing the Rcd (parallel conductors) - It may only
be a tiny amount flowing via the cpc but it only has to be 20/25 mA
and...trip
The likes of the TV etc probably won't draw enough to do it.

That's my bet anyway - looks like you might be spending the day
splitting the ring

 

[uksel]

i always do an IR test on all the circuits before removing a CU to change it, any suspect readings and the changeover stops.

 

[bugsy]

Well Lloyd did you sort it

 

[lloyd1980]

just got back from there now guys
what a nightmare!!
IR tested all the circuits individualy with everything unplugged lamps removed, everything meggered out ok with good readings
then i ramp tested rcd - fine -
split rcd so I tested the other - fine
there were 3 original lives coming out the mcb id installed so i connected one with everything else off, and found the other live ( the ring) and dissed the other non live one including its neutral and just left the ring
this stabalised things with the ring, as in toaster kettle microwave all going and it was holding
tested what was dead to see what the dissed cable fed
it was a fan heater in his bathroom from a fused spur.
so at this point ring is ok
try the cooker, pop goes the rcd
i move the cooker over to the rcd thats holding with the ring try it again - pop
I megger the cooker cable again - >299 on meter so ok
im thinking faulty rcds, so spin down the wholesalers and change them, some back fit the new ones
exactly the same problem
all his impedances are excellent and everything meggers out like it should
I advised the old fella, that his work wasnt helping things, as in lots of lighting and flurecents wired in flex and double sockets he'd fed from plugtops all over in flex all neatly in trunking werent helping matters, he knew a little about electrics but was convinced he knew everything so how dare I question his work - even tho it was sh ite
I then told him I was getting a mate down as 2 heads were better than one and I would get to the bottom of it!
He instructed me to stop work there as he didnt want the extra cost of the investigation, and he instructed me to re-fit his rewirable fuse board
told him I could not sign this off as old board
he didnt care and insisted I did it
So i spent time then refitting his old board ( thanks god I didnt skip it yesterday) and got him back on
he then wanted to discuss the estimate as no new board - advised him I couldnt take it back to wholesalers as been used so cant knock it off the price
I tested his whole flat and refitted his old board at the original estimate cost (new cu) and have done loads more than I charged for
I just hope when his daughter goes round and sees the 17th edition board sitting there in his cupboard and the original one in and all it looks like hes had done is a new 10mm shower cable and a 2.5 immersion feed, she doesnt sla g me off saying ive charged him for doing nothing
I really did want to get to the bottom of it too but he just point blank refused and insisted on his old board
advised him he is living with big problems and it needs attention but its falling on deaf ears and his mrs who is just as old is more concerned that the cooker and kettle work now rather than the conditioning ofd the wiring
thanks god my name isnt on the cert
so I am quite releaved!!!!!

 

[JulianC]

Aww man, now we'll never know what the problem was. Get back down there and tell the old fella you won't leave until you've found the cause of the problem. No charge of course.

 

[lloyd1980]

I know!!!! I really wanted to know what was causing it!!! it had me intregued!!
I have stuff booked in now so am not going to sacrifice time off another paying job to look at a problem he doesnt care or isnt bothered about.
ive done more than enough work there that ive not charged him for to do more.

shame about not finding it tho I agree!!!!!

therell be another one next week somewhere, bloody DIY'ers