What could have happened?

[MrHumbug]

So at the weekend I decided to get on with a job I've been meaning to do for a while. There is a single socket in our loft, spurred from a socket on the downsatirs ring in the bedroom below (you can see a slightly uneven bit of plaster where the wall was chased). I wanted a couple more sockets up there for low power stuff so the plan was to replace the single with an FCU then feed a couple of double sockets from there.

I switched off the mains at fuse box (I say fuse box because it's one of the old style wired fuse ones - although it's been retrofitted with MCBs). Pulled out the MCB labelled 'Upstairs sockets' (because I'm not risking someone else in the house switching it back on for me) and switched back on. Peculiar thing is the upstairs sockets are still live. Oh dear.

I switched off the other two 30 amp MCBs and the sockets went dead. After a bit of trial and error decided that they were being fed from another 30 amp feed that was unlabelled. So with main switch OFF I opened the front of the box and note two 2.5 mm cables in upstairs sockets and one in the other 30 amp feed - yes one 2.5mm on a 30 amp feed!

Anyway to cut a long story short, it turns out that the upstairs ring is connected to two 30 amp MCBs (one each end) and the other cable is a radial to the socket for the washing machine.

Sorted the connections out properly, swapped the MCB on the radial for 15 amps and while I was at it noted the 1.5mm cable for the outside light should be on a 6 amp MCB, not 15 amp (so I only had to buy a 6 amp one).

I know the earlier situation was A Bad Thing, but just how bad could it have been?

And I suppose you'll now tell me that I should have notified the LABC before reducing the size of the MCBs.

And yes, I think I will get a PIR in the near future.

 

[swidders]

You shouldn't run a radial circuit as a spur from another radial circuit, which is your intention in the loft.

 

[Spark123]

Worst case scenario is that you could overload a circuit and cause a fire.
Technically you should have notified your LABC yes (I wont tell if you dont)

 

[ColJack]

emergency repairs to correct a dangerous situation.. you can notify them after the fact, but make sure you DO notify them..

the ring could have overloaded and melted then burt into flames..
seriously..
you could draw 60A before either breaker would blow.. with the exception of the one with the radial in it too, that would blow sooner if you had a load on the radial..

 

[kevindgas]

Anyway to cut a long story short, it turns out that the upstairs ring is connected to two 30 amp MCBs (one each end)

Are you sure about this? a ring or a radial should only be connected to 1 MCB!

And yes, I think I will get a PIR in the near future.

i think this is wise i light of above

 

[ColJack]

swidders, he's not..
he's turning an unfused spur from the ring into a fused spur and running the new sockets from that..

 

[ColJack]

kevin, that's what he found, not how he left it, he corrected it..

I do wish some people would read slower, they keep missing bits...

 

[swidders]

swidders, he's not..
he's turning an unfused spur from the ring into a fused spur and running the new sockets from that..

Didn't think this was permissable - in effect running more than one socket on a spur from neither radial nor ring. It's good to learn.

 

[MrHumbug]

you could draw 60A before either breaker would blow.. with the exception of the one with the radial in it too, that would blow sooner if you had a load on the radial..

That's what I thought. Luckily we've never plugged anything big or faulty in.

 

[ColJack]

providing you use 2.5mm cable, and depending on the installation method and derating factors, a single unfused spur is allowed from every connection point on a ring if you want to.. ( for those not in the know, that means the back of sockets and suchlike ) ..

this spur can consist of ONE single or double socket ( where the load is limited to 13A or 26A respectively.. ), or a fused connection unit connecting a single piece of fixed equipment.. ( thus limiting it again to 13A )

a fused spur allows for any number of sockets or EXTRA fused connection units ( as the first FCU limits the total load to 13A ).

 

[swidders]

a fused spur allows for any number of sockets or EXTRA fused connection units ( as the first FCU limits the total load to 13A ).

Well, I never knew! So the FCU is acting like a 13A plug into which you can add a load of extention cables. I'm starting to sound like a brunette now, so I think I'll eff off back to general and plumbing where I belong

 

[MrHumbug]

emergency repairs to correct a dangerous situation.. you can notify them after the fact, but make sure you DO notify them..

Wiyll they still charge me £100 or so to come and look at my shiny new MCB and tick it off on a form? 'Cos if they will I'm not telling anybody where I live.

 

[swidders]

Wiyll they still charge me £100 or so to come and look at my shiny new MCB and tick it off on a form? 'Cos if they will I'm not telling anybody where I live.

Rub a bit of dirt over it.
Right, I'm off

 

[MrHumbug]

Oh dear. I seem to have had an accident with the hoover bag in the vicinity of the fuse box ...

 

[ColJack]

I hope you're not all condoning breaking the law?