Fusebox being fed by a ring main

[Crazyk]

Hi guys

turned up to a residential property today to add a few double socket outlets only to find the fuse box in the area was being fed by a ring main on the main switch. Is this allowed ?

 

[micknew]

diyer.................

 

[Marvo]

So there's a main CU supplying a socket ring main which in turn supplies another fuse box....is that correct? What is the fuse box supplying?

 

[Crazyk]

3 rcbos ( 16amp with 2 double sockets 1x20amp feeding 3 double sockets, 1x6amp feeding 6 6watt led spots

 

[micknew]

Perhaps he intends doing the fuse box addition tomorrow, just checking if its acceptable lol.

 

[Crazyk]

No this is existing, I am checking if its acceptable

 

[Marvo]

I'm confused, when he said 'fusebox' I imagined fuses. I really don't understand the layout....

 

[ExArmy]

are you an electrician?

 

[Crazyk]

Main fuse box then off of this goes to another fuse box using a ring main as a sub mains

 

[Crazyk]

Surveyor

 

[ExArmy]

well whats the ring thats feeds it fused at? it probably doesn't break any regs, but is liable to be overloaded and trip the MCB feeding the ring and DB.
is it an actual ring main , with sockets, or is it just a sub main wired up with 2 x 2.5mm conductors?

 

[Crazyk]

It feeds 4 other double sockets as well and fused at main DB at 32Amps

 

[Crazyk]

Apparently been like this for 4years

 

[ExArmy]

well these proposed new sockets could be the straw(s) that breaks the camels back!

 

[Richard Burns]

This is likely to work but not to be suitable for installation. The possibilities for overloading a cable are very real. However in normal use a socket circuit does not draw much power.
A ring final can only have a spur limited to 13A or a single double socket attached to it.
Effectively this is creating a very high current draw potential at a single point, which is not the intention for a ring final.

 

[Crazyk]

Thanks

 

[Guitarist]

There was a thread about something similar a few months back. It's quite common to find garage boards fed by a 2.5mm RFC (I've come across a few myself), on installs carried out during the 70's, as this was seen as a cheaper alternative to 6mm on a 30 amp fuse.
Obviously, in this case, the RFC is straight off the main switch which is very naughty.

 

[telectrix]

but this scenario appears that someone has tapped into a RFC to feed a sub-main. not good, IMO.

 

[stranded]

I'm confused, when he said 'fusebox' I imagined fuses. I really don't understand the layout....

Havent a clue... I imagined fcu's....

 

[Guitarist]

but this scenario appears that someone has tapped into a RFC to feed a sub-main. not good, IMO.

I read it as an RFC straight off the main switch of the original board to feed the sub-board. Happy to stand corrected though.

 

[telectrix]

he's not made it clear.

 

[Guest55]

is it a good design - course not.
is it normal practice - nope
is it dangerous - not really

no matter what you add to the ring and however its wired its still limited to 32A.
if you replaced the remote CU with 3 spurs to feed those sockets and lights no-one would bat an eyelid.
the only downsides are uneven loading of the ring legs and no dicrimination between the mcbs.

must dash now , tels pulling a fast one in our chess game lol..........

 

[Octopus]

is it a good design - course not.
is it normal practice - nope
is it dangerous - not really

no matter what you add to the ring and however its wired its still limited to 32A.
if you replaced the remote CU with 3 spurs to feed those sockets and lights no-one would bat an eyelid.
the only downsides are uneven loading of the ring legs and no dicrimination between the mcbs.

must dash now , tels pulling a fast one in our chess game lol..........

Sorry Biff but I HAVE to disagree. You could easily overload the RFC with such a configuration and it needs to be reviewed/improved. Anyone adding further sockets/breakers to the DB needs their bumps felt.

 

[Guest55]

Sorry Biff but I HAVE to disagree. You could easily overload the RFC with such a configuration and it needs to be reviewed/improved. Anyone adding further sockets/breakers to the DB needs their bumps felt.

what happens when you overload a circuit protected by a mcb thats correctly rated for the job ?
it trips.......

 

[Guitarist]

If, as I read it, the RFC feeding the sub-board is taken directly from the CU main switch, then it IS dangerous, as there is no protection for that pair of T&E other than the main fuse. If, on the other hand, it's as I sometimes see it (An RFC from a 30 amp fuse feeding a sub-board), then as Biff says, it's protected and safe (however rubbish it might seem).

 

[cobrauk]

I have seen this happen before, when kitchen fitters have been around they do it so that the sockets etc within the area they are working comply with the regs as far as being protection via Rcbos.

Like others have already said it protected via 32amp so no overload to worry about

 

[Engineer54]

I read it as an RFC straight off the main switch of the original board to feed the sub-board. Happy to stand corrected though.

He did say this!!

It feeds 4 other double sockets as well and fused at main DB at 32Amps​

 

[Engineer54]

I would say that this spur off a RFC has now got out of control. You can't just keep adding to this spurred off CU, which may have been all well and good originally, just to supply a couple of sockets and a bit of lighting. Up to you, but i'd personally decline supplying any more sockets to this spurred CU, ...enough is enough!! lol!!

 

[Flanders]

You could end up running the RFC at 32 amps constantly, a RFC is design with diversity in mine i.e. it will not run 32 amp all the time I have seen a RFC
installed to supply 3 heaters, T&E had over heated and gone brittle when I check current draw it was between 30 and 34 amps

 

[mechelec]

I would have thought the major problem with this design is the size of the spur cable. If 2.5 T & E then this would almost certainly be overloaded. If the board was spurred off the RFC via an FCU with 13A fuse fitted then it is still a poor design but not dangerous. If the the spur is 4mm then not quite as bad but poor design due to loading in one section of RFC.

 

[Guest55]

You could end up running the RFC at 32 amps constantly, a RFC is design with diversity in mine i.e. it will not run 32 amp all the time I have seen a RFC
installed to supply 3 heaters, T&E had over heated and gone brittle when I check current draw it was between 30 and 34 amps

cant believe this post hasnt been pulled........

2 x 2.5mm T&E legs combined is good for around 50A clipped direct so i dont see how
32A is going to trouble it in any way ?
and i guarantee if you were to test the cable to destruction it will probably carry double that before the insulation is toast.
absolutely no design issues arise when running a properly installed circuit to its max mcb rating , hence the cornerstone principle of In > or = to Ib.
diversity doesnt even come into it IMO.