Head scratcher

alphonse mephisto

I was working in a large and badly wired house today, the place has four consumer units and its all a mess. Done a buch of fault finding but one im stuck on is the garden lighting.

Its all wired in 2.5, on 20amp type b, there are 8 mains voltage lights with energy saving bulbs spread out over about 80 meters.

At the board its wired MCB - TIMER - MCB - CONTACTOR - MCB - LIGHTS

They work fine for an hour or so then trip the 2nd and 3rd MCB.

I done what testing I could ( no megger today ) and found nothing wrong.

I got to thinking that full load current was to much for type b but highly unlikely.

Found a random 1.5 stuffed into the bottom of the timer and got to thinking some sort of fault was being imported. Disconnected it and powered up again, the lights where on when I left but I had already been there 12 hours and didnt feel like camping!

Any suggestions or questions just shoot!

Thanks lads!

mikehammer67

you'll need a megger anyhow

to test outside wiring with bulbs removed


they wont trip a B20 mcb unless there's a problem



just hook the cable feeding garden lights into a separate mcb(to prove it) if you can't figure out the wiring setup as it seems bizarre

liveandnetural

the megger is your friend on this one

what wattage are the lights in the garden (total them up, then mesure the current flowing and see is it same)

most likely water in some of the lights

frankmul

If it is an overload, changing the mcb down in rating might get the fault to occur quicker.

Bruthal

Probably water into connectors or light fittings causing intermittent shorts. Outside lights are a nuisance unless any junction boxes are properly filled with resin. Is it all MCB,s or is there an RCD in the circuit too? Double pole switches on the circuit before it leaves the house helps to find problems later as well, especially on RCD protected circuits.

alphonse mephisto

Its been bone dry down there for a few weeks so i cant really seeing it being water but I do appreciate the suggestion and will check when im back there.

Like I said the electrical is very messy, which is strange because everything else seems to be done to a high standard.

I honestly wouldnt be surprised if that entire board is powered by an RCD from one of the other boards.

What would be the exceptions if any to lighting circuits tripping an RCD?

Im going have to map out everything, megger everything and at the least recommend rewiring two of the boards I looked at. Three unrelated electricians wired the place and if you looked at it you would be shocked. One RCD is protecting five MCBs and they have 17 cables of various sizes stuffed into them!

Its mad!

Thanks for the input lads, keep it up!

cast_iron

alphonse mephisto wrote: »

One RCD is protecting five MCBs and they have 17 cables of various sizes stuffed into them!

Its mad!

While not ideal, that doesn't necessarily need to be rewired I would have thought. "Doubling up" wouldn't be that uncommon. Perhaps there's a rule against it...other might know, but not necessarily that dangerous imo.

mikehammer67

cast_iron wrote: »

While not ideal, that doesn't necessarily need to be rewired I would have thought. "Doubling up" wouldn't be that uncommon. Perhaps there's a rule against it...other might know, but not necessarily that dangerous imo.

'bunching' it's called-doubt there's any rules against it

'paralleling' would be a different matter-if they were doubling up cables to make the capacity

Mr.Fred

alphonse mephisto wrote: »

At the board its wired MCB - TIMER - MCB - CONTACTOR - MCB - LIGHTS

I'd have thought this set up was wrong anyway.

Surely all that's required for a control circuit would be a 6A for T/C contactor then a 10A supplying the lighting broken through the contactor.

6A Mcb - T/C - A1 (cont)

10A Mcb - supply to lights broken through contactor.

At least that's how i'd have done it although with only 8 mains lights with cfl lamps there would probably be no need for the contactor.

10A MCB - T/C - Lights

Just my 2c

mikehammer67

10amp mcb>mechanical timer>lights

is all that's needed here



if you have photocell or digital timer you might add a modular contactor

Bruthal

I'd be sticking RCbo on it for garden lights anyway.

mikehammer67

Bruthal wrote: »

I'd be sticking RCbo on it for garden lights anyway.

yes for new work always

if you're just troubleshooting............

alphonse mephisto

I had a quick look at the regs this morning and if im picking them up wrong please let me know.

for parrallel conductors the cables must be same cross sectional area with a minimum of 10 square, be made of the same material, be exactly the same length, not allowed in domestic, have short circuit protection on each end etc etc..

Yeah ive seen bunching/parralleling heaps of times im just not that into it. its one thing doing it if your short a breaker or there is no room in the board but i just dont feel its a good practice.

ill suggest rewiring it to him because of among other things the RCD had been by-passed with .75 flex so it had been overloaded and tripping from time to time at least. its like a birds nest made of cables in the thing and i switched off an MCB to work on a lighting circuit in the basement and some of the sockets upstairs powered down too so its just not good!

As is whats there would fill a three row board and if the owner wants it done great, it will be nice, neat, clean and labeled. If he dosent thats grand too but the next sparks in will be the fifth.

Anyway, id go RCBO-switch-lights, at least the people living there would be able to knock them on and off without having to climb a ladder in a basement! ha

Thanks lads, have a good weekend!

mikehammer67

alphonse mephisto wrote: »

for parrallel conductors the cables must be same cross sectional area with a minimum of 10 square, be made of the same material, be exactly the same length, not allowed in domestic, have short circuit protection on each end etc etc..

ya that's 'paralleling'-there's restrictions on that(as quoted)


a few 2.5 radial circuits shoved into a 16/20amp mcb isn't paralleling

think it's called 'bunching'

i'm not aware of any rules outlawing that

2011

alphonse mephisto wrote: »

for parrallel conductors the cables must be same cross sectional area with a minimum of 10 square, be made of the same material, be exactly the same length, not allowed in domestic, have short circuit protection on each end etc etc..

Mike is correct, this is not paralleling.
Paralleling would be when the cables connected to the same supply are sharing a common load.

alphonse mephisto

Alright so, thanks for putting me straight there.

Everyday is a school day I think is the saying!

Yeah I had a look for bunching there also and the regs had nothing to say about it that I could see anyway.

mikehammer67

bunching is prob a slang term i've heard used
doubt it would be in the index

Bruthal

The difference between doubling up (bunching) and paralleling cables to a load is common sense really.

A ring main socket circuit could be said to be a form of paralleling.