Two radial circuits into one MCB

[New Venture!]

This type of thing may well have been posted before so apologies if it causes some members to groan!

Over a brew today a younger sparky asked what we thought of putting two radial circuits into one MCB. He asked as he'd been replacing a rodent damaged ring but due to the house being occupied and moving furniture/lifting carpets to complete the ring being a PITA he installed two 2.5mm radials and connected them back to the board into one 20 amp MCB. His foreman wasn't pleased. 

I couldn't see any issue with this. He used max test reading values on his certificate, the area covered was fairly small and the cable installation method meant 2.5 T&E was able to handle 20 amp. 

Have I missed something? 

 

[steptoe]

seems perfectly acceptable to me,

albeit not ideal, you dont have the benefits of them being radials,

but, not, AFAIAA, contravening any safety issues, just the inconvenience reg.

 

[Andy™]

ideally it would be on 2 breakers to split the wiring up a bit more, but there is nothing wrong with 2 'circuits' on 1 MCB

 

[Lurch]

I have said this a lot of times on this forum, 1 CPD = 1 circuit.

You cannot put 2 circuits in 1 MCB, 1 MCB cannot supply 2 circuits.

 

[New Venture!]

Pretty much how our tea break chat went!

 

[ProDave]

As Lurch says, it is all ONE radial circuit, it just happens to branch two ways from the mcb.  You could probably go to a 25A mcb at a push.

I presume lack of space in the CU prevented him making it two circuits?
 

 

[New Venture!]

Yup, only one spare way on the CU. 

 

[Evans Electric]

Or looking at it the other way ...its one circuit going in two directions ......Or it comes from one breaker so its one circuit . 

I can't see a problem , in fact I've done it a few times myself .  Circuit is protected by a 20A  breaker , what,s not to like .

 

[ProDave]

Yup, only one spare way on the CU.

so it used to be a ring on one mcb with one spare way.  Use that spare way to make it two radials?
 

 

[New Venture!]

Sorry Prodave, confused things. Only one available slot, made available by removal of the 32 amp that was feeding the knawed ring. 

 

[Jono Pashley]

Made the best of a bad situation by the sounds of it.

 

[SLIPSHOD & SLAPDASH]

Nothing wrong with method.

 

[Doc Hudson]

How is this any different from having a branch at any point in a radial circuit?  A radial circuit is permitted to have branches,  have a look at the pictures in appendix 15.  If you had 6 sockets  A,B,C,D,E & F all connected back to one MCB, but (E & F) were a 'branch' of the radial.  (E & F) could quite happily be branched at A, B or C or even at the MCB without causing any danger to people, property or livestock. Which is one of the underlying fundamental principals of our regulations.

Doc H. 

 

[Andy™]

same as you could connect a spur to a socket in 2.5mm directly to a 32a mcb... seen many times when people complain when its taken from the MCB terminals but nothing said when its done for another socket...

 

[Tony S]

OK let’s take the RFC/Spur argument to the point of lunacy.

 

[Sidewinder]

You can't quite go that far and be compliant Tony.

You are only allowed one unfused spur from a single point, and the circuit OCPD is a single point, so only one spur from the MCB.

View attachment BS7671-Amd3-App15-Fig15A.pdf

 

[Sharpend]

Concur with the snake on this one. 

 

[Sidewinder]

Mind ridiculous as it seems, apart from the one spur on the extreme end, it is otherwise compliant.

 

[Tony S]

You can't quite go that far and be compliant Tony.

You are only allowed one unfused spur from a single point, and the circuit OCPD is a single point, so only one spur from the MCB.

View attachment 7597

Concur with the snake on this one. 

Mind ridiculous as it seems, apart from the one spur on the extreme end, it is otherwise compliant.

It was just a p*** take but you can see just how daft the setup could become

 

[binky]

I have said this a lot of times on this forum, 1 CPD = 1 circuit.

You cannot put 2 circuits in 1 MCB, 1 MCB cannot supply 2 circuits.

totally disagree, I have frequently repaired broken rings by down-grading to a 20A MCB where access to cables is difficult. As long as the board is correctly labelled, there is nothing wrong with this albeit it may not be ideal. Likewise it is allowed to take a single socket spurred off a 32A MCB, again, not my preferred way of doing things, but that is more to do with not always being able to clamp 3 conductors effectively in a single breaker.