At the risk of making myself look a bit of a.......

[Sparky83]

....Pratt!

I was having a disscusion with a mate of mine and radials (like you do)

and we disagreed on on feeding a 2.5mm t&e from the 32a mcb of a ring ciruit.

I thought that you could only spur off the ring from a point on the ring itself like a socket, but he said you could take it straight from the mcb itself. To me this then becomes a radial circuit sharing a mcb with a ring main?

What would happen if the ring was removed and the radial circuit left, on a 32amp breaker, that would be right, so what makes it ok when a ring shares the mcb?

I've had a look about and even on this forum but some say its ok some dont. Im happy to admit im wrong, which is how it would seem it is but i would like a good explenation as to why its ok.

Cheers
Shawn

 

[Baal]

It's perfectly acceptable to spur from an accessory, a suitable junction box, or the protective device, remember that a twin socket is still only rated at 13A

 

[Hawk81]

its ok because the brb says its ok. i see your point and agree. as with alot of stuff in the brb i dont agree.

 

[mark80]

Well whether you spur straight from the MCB or from another socket, either way a 32a MCB is feeding a single 2.5mm cable.

 

[Addlight]

There's a big difference between adding a radial to the same MCB that is protecting a ring, and adding a spur to the ring. It sounds like you mate is saying you can add a radial to same MCB as a ring - at the MCB itself. Definitely not: one circuit per protective device. A radial from a 32A would need 4.0mm anyway. But spurs of accessories on a ring can be 2.5mm.

P 362 of Regs, btw...

 

[Amp David]

The part about 'if someone was to remove the ring and leave the radial in place', well suppose this is why only a compentent person should only complete works of this kind.
Anyone who had checked to see a radial was supplied from the fuse would surely fit a smaller fuse or breaker

 

[Amp David]

The big red one only says you can pur from a fuse not add a radial to it.

 

[martysparky]

I think the question to ask is who would take the ring out if it was being done. If a competent person then they would down rate to 20A but if Mr DieWhy would he.

I was taught not to double up but have read that you can spur from CCU. So personally I would avoid it.

but a spur should be 1 double or single outlet, or if more sockets required protected by a 13A F/C/U

Interested to hear other thoughts too. Edit, that was quick guys!

 

[Baal]

Guys, check the on-site-guide page 54, as I said, it's perfectly acceptable.

"such a spur is connected to a circuit at the terminals of a socket outlet, or at junction boxes, or at the origin of the circuit in the distribution board"

 

[martysparky]

or App 15 BRB

 

[Amp David]

No ones saying it isn't

 

[ezzzekiel]

i am.....

oh actually im not

 

[Baal]

That's not how I read Addlight's post?

 

[Amp David]

Addlights just saying that you can't add a 2.5 radial from a 32amp breaker protecting a ring.

A spur is one thing, a radial is something else

 

[Sparky83]

So what is the difference betwwen..........

A) 2.5mm on a 16a (or 20a) mcb radial circuit
and
B) 2.5 fed from a 32a mcb that also feeds the ring

(Both 2.5mm cables are feeding 1 double socket)

In (A) the cable is protected by the mcb as it is lower the the max for the cable, but in (B) it is not, it is over the max for the cable.

I understand that it is ok to do this i just dont really get why.

When i said about taking the ring out and leaving the radial behind i was being hypathetical just to get my point across that it seems that regardless of the fact a ring is sharing the mcb it is still a radial and should therefore be protected accordingly?

Im sure this is just me missing something, but i dont get it!