Diagram for finding a fault on a ring main

[AndyPRK]

I would think you would disconnect both cables from the CU

and then insulation test, (or resistance test if you havn't got one) between the L / N / E connections to see if there is a short. (unplug everything first and switch off FCU's).

Is it an RCD or MCB that's tripping ?

You may struggle with test equipment you have, but you could disconnect one half of the ring safetly and try it like that for a few days and see if the tripping stops

 

[meb97me]

ah, of course after splitting the ring if theres a short it will show up by bridging the L N E wires with a multimeter in turn at the CU end won't it, doh!

We had a sparky out a while ago as an emergency fix and he's basically unconnected half the ring as far as i can tell as its no longer tripping. However there's only 1 set of wires in the breaker now (the others are just disconnected in the CU) but we don't have power in our porch or the front room (which we don't use at the moment) but he's not been back to sort it yet as we are having some other refurbushment work done at the moment so the £350 he quoted for rewiring meant we had to put it off temporarily.

Oh its the RCD thats tripping iirc

cheers for the pointer

 

[bernardgreen]

An RCD can trip when there is a load on a circuit (A) and a neutral to earth fault on another circuit (B). Because the RCD most often trips when an appliance is plugged into circuit (A) is it easy to consider the fault is on circuit (A) when in fact the fault is on circuit (B)

Neutral_Earth_trip

• bernardgreen
• 16 Jan 2011
• 48

Unfortunately some "electricians" will spend a lot of time looking for the fault on circuit (A) instead of carrying out insulation tests on all the circuits the RCB is protecting.

 

[meb97me]

I won't pretend i understand that last diagram i really haven't got my head around mains electrics and the science around shorts but i can do basic fault finding/connecting up.

The problem appeared overnight one day, we woke up and it had tripped, however when i tried to turn it back on again it tripped again instantly. I went round and pulled everything out of all the sockets and yet it still would trip so i'm guessing it must be a short somewhere in the ring wiring.

It's weird as we've definitely not done any work, put any nails in walls etc prior to it tripping and i'm pretty sure we don't have a rodent infestation so more investigation is required

Anyway its a job for the bank holiday weekend whoopee !!

 

[garlicbread]

I had a fault recently, took a while to narrow it down. Found the leg that was affected, L/E fault. Checked the wiring under the floor boards everything seemed fine. Cable entry to sockets fine, and no DIY work had been done. What it ended up being was who ever installed the skirting boards years ago, put a nail through the cable, but it only went through the live wire and into the wall. Over time he had a problem with damp on the wall and it was only when it had been raining that it would trip the mcb (no rcd).

 

[meb97me]

Well I managed to sort it last night.

Turns out in one of the sockets that the ring had been disconnected so effectively we had 2 spurs powering the downstairs, and in the socket where the ring had been broken the live and neutral had been taped up but not very well and we're touching, so the spark had disconnected the spur at the cu which obviously had sorted the tripping but left us with numerous non working sockets.

Any way I connected ring back up and reconnected wires at cu and we're back in business.

Happy days

 

[333rocky333]

We had a sparky out a while ago as an emergency fix and he's basically unconnected half the ring as far as i can tell as its no longer tripping.

Did he also derate the MCB at the time, if so you may need to uprate it back as it was, now you say the rings reinstated

 

[meb97me]

No he didn't replace anything he simply disconnected the cables at the cu which stopped this shorted spur from tripping

 

[securespark]

Its not unknow to have a fault on both halves of the ring, which will leave you scratching you head for quite a while.

Aye!

Or, in my case, before a board change, I tested a ring final and found one fault on one side and TWO on the other..... ARRRGGGHHHH!!!!

One of the faults was a deliberately introduced link in a socket outlet between neutral and earth....

 

[AndyPRK]

Was Anna Robinson testing you ?