Ring Main Issues - After 1/2 a Job!

[BottleShopMan]

HI - wondering if you guys can help / shed some light.

i took over an old shop in a really old building - i doubt much had been done electrically since the 70's and the prev tennant was a very bad diy'er!

now in a previous life i worked on various different sites, telecom exchanges and the like so i know how to terminate and run cables as ive done it (under supervision lots of times) but im not a have a go hero type.

So as the elecs were a minefield of old and bodge we had a new CU fitted (by an electrician provided by the landlord) all the cables were run to the required places and 90% of the sparks worked fine.....

then the guy kept not showing up etc so was let go. then issues with the elecs became apparent!


the problem i have is -

a ring main (for the back room sockets) running from a 16A Trip on the CU - which was working. now doesnt

i was up building a loft space in the rear of the shop so i was at height and close to the wires i saw the ring main was looped back and joined to the lighting for the same room (and empty slot on the CU) at first i thought it was a miss label but the cable size made me want to check.

i did by isolating each trip and circuit it WAS wired back to the lighting

so i re instated the circuit as a proper ring main (the other cable was in the same channel as the lighting.

now the sockets all test ok with a socket tester (i know they are not the font of ring mains) - i had to re terminate some sockets and the internal wiring on some was shocking.

but when i add load the board trips -

there are 7 sockets on the circuit with 2 ring proper, 1 juction off ring, 2 spurs, then 2 additions to the spurs.

the landlord has said he will provide another elec but hes on holiday (landlord) so it could be a week!

is the problem that the prev guy has joined spurs onto spurs? i thought that was a no no

im a bit wearing about the landlords choice of trades but id like to at least be better armed with the likley causes of the fault so im not taken for a ride again.

i can answer questions if this doesnt make sense

thanks

 

[plugwash]

Is it a split load board (either with rcd/non-rcd or multiple RCDs)? is it a RCD that is tripping?

If the answers to both those questions is yes then you have most likely put the neutral in the wrong neutral bar.

 

[BottleShopMan]

Hi

Thanks for the reply - the CU Board is split via 2 RCDs RH and LH

LH has the majority of sockets etc on

RH only has 2 breakers (water heater + Glasswash) both biggies for added load.

the board trips on both RCDS when load is applied to the circuit im having trouble with

if it is a neautral in the wrong bar as the CU was fitted by the ex guy would it be something i could check visually?

 

[securespark]

Yes, providing the circuits are not wired in singles.

 

[BottleShopMan]

Thanks

i took the board cover off the main board just to see if i could see anything loose.

the neutral bar had 2 terminations, so i took the main conduit off above the board....

and found that the 2 wires feeding that breaker - 1 of which had a double choc box / tape joint!!! (see pic) and this was done by an electrician!

so i will try replacing that joint and see if that helps!

thanks i would never have looked behind there as id assumed the work was done properly!
//media.diynot.com/228000_227071_90280_63849647_thumb.jpg
i will let you know if this fixes things.

Untitled

• BottleShopMan
• 18 Feb 2015
• 1

Untitled

• BottleShopMan
• 18 Feb 2015
• 1

Untitled

• BottleShopMan
• 18 Feb 2015
• 1

 

[PrenticeBoyofDerry]

If the both RCDs are tripping when a load is applied (out of interest what load is being applied?). Then it is highly likely that the neutrals are shared across the splits. This could be at the board, but maybe not.

 

[securespark]

If it trips when operating light switches, it may be a case of a "borrowed neutral".

Just re-read your posts.

It was working until you made alterations: is that right?

If so, un-do the work you have done and see if it stops tripping.

2 RCD's tripping under load points to swapped neutrals somewhere.

EDIT: Apologies to PBOD who has already pointed this out.

 

[BottleShopMan]

So ive traced out the neutrals on bar 6 (the socket Breaker) they led to the crap joint. i repaired that. still tripped

the sockets did all work when it was wired as follows;

CU out -(6 back sockets) --- Sockets ---- (4 back lights) - return to CU

the return wire to the CU after the sockets for the (6back sockets) was terminated at a isolated junction box.

i think what may have happened is the guy ran the cable and maybe miss labeled and confused them? as they worked he left it and didnt correct the labels or check the circuits. as i have a second pair of hands i will trace back from the CU again just to be sure.

as the 4 back office lights has nothing attached i have turned the trip off.

would this being off cause the ring to trip with a load if it was run back to the lighting (off) breaker ?

 

[securespark]

Disconnect the neutral for that lighting circuit and see if it changes anything.

There could be borrowed neutrals on that lighting circuit.

Whatever the cause, there is a huge cock-up somewhere and it needs to be found.

 

[BottleShopMan]

OK so pig of a day.

we physically traced the cables out which meant moving lots of built in shelving. this meant we could be 100% the right cables were running to the right MCB

we even disconnected all pre run cables for MCBs not yet in use. so im confident that the given ring main was terminated in the right MCB.

still the RCD tripped when load applied.

re checked socket tester said neutral earth reverse which i know can sometimes be a dodgy connection so re checked. no trip but no power.

when the load is applied the MCB doesn't trip only the RCD?

i dont know if that tells you anything?

ive been on the phone to the landlord and other elecs to try and get someone out to see if they can resolve - fingers crossed next week

but not a happy bunny especially as the kettle should be on that ring main!

 

[securespark]

Did you try disconnecting that neutral?

You said the lights were linked to the sockets?

Guess it didn't change anything?

OK, so you still have a fault.

Try disconnecting each circuit's neutrals now one by one (put them in a choc block to make them safe) then see if it still trips.

You should get to a point where if you have disconnected the load that is imbalancing the system, it should stop tripping out.

Did the spark do any tests before he bu99ered off?

Like RCD tests or IR?

 

[EFLImpudence]

checked socket tester said neutral earth reverse

Socket testers can't distinguish between Neutral and Earth.

 

[BottleShopMan]

the ring main and lighting circuit in that room are seperate.

the confusion was the ring main had been wired back into the return for the lighting - when i changed it back the probs started.

i have removed the whole lighting circuit for that room as its not used and was confusing things (the walls are old and have lots of old redudndant cable in them still and pinch points where lots of cable has been run and left in situ)

the prev elec was the landlords guy - having seen a spark do an install of the same model CU in my house (after the shop fitted) the difference in amout of time and work i saw between them was night and day.

i did try taking the neutrals out for the ring main - no trip but obvs no power.

i didnt take all the other neutrals off one by one as id not had problems with the others (been functiioning for 6 months so far)

i will try disconnecting each neutral in turn tommorrow - see if i can at least find something to point the next spark at