Maximum number of conductors in MCB for radial circuit?

[cornburn]

I can't find anything in the regs. On a ring it's fine to run a spur from the MCB (so 3x2.5mm). On a radial technically it doesn't matter where connections are made to the circuit as long as the cable at any given position can withstand the load. So how many connections from the MCB would be acceptable? Would you go by manufacturer's recommendation as to how many the terminal can hold?

I have to add 2 sockets into a radial run (currently a mix of 2.5mm & 4mm single cores and T&E on a 20A type C MCB). I could break into the main leg of the radial from a steel conduit inspection bend and leave a wago box hanging out of the bend (a bit messy IMO, even though hidden above a ceiling), but it's only about 6 feet further to the board so I'm thinking of just coming off the MCB instead. There are currently 2 connections in the MCB and it got me wondering how many you could technically fit.

And before anyone asks, this radial is the only RCBO on the board so I want to come off this circuit to save spending £100 on a Merlin Gerin RCBO just to put 2 sockets in.

Let the arguments commence..............................

 

[DurhamSparky]

hmm tricky one this, i have installed 3 radials from a MCB before for different lights, i assume as long as you have a decent connection and you do not stress the MCB retaining screw then as many as you deem practical. (obviously IAW Manufactures installation instructions) and don't over load the MCB!

 

[GT1]

yes im waiting with baited breath for the replies on this. Tried to find a similar answer some time ago and never reallly came up with an answer i was happy with..!

 

[Mr.Black]

Phone up your Part P scheme provider and let them earn their money.Then that way if it gets pulled for assessment..hey presto it was them that advised you .

Let us know what they said though.....

 

[Sintra]

have a read at reg 523.8 conductors in parallel. in my opinion 1 cable at mcb.

 

[acat]

I agree with above apart from anything else how much power would the client lose in the event of a trip of the MCB.


Chris

 

[ezzzekiel]

I would teat as a spur so never more than two at mcb although nothing wrong with radiating out from source like spokes of wheel except for space constraints

 

[bugsy]

I'd spend the extra £ 30.00 and install new RCBO = proper job

 

[Davey101]

Have been picked up on this by one of my fellow testers. Sintra is correct I believe, only one connection at an MCB except on a ring/spur arrangement (which seems backward to say the least).
On a practical level, I would have no problem with seeing two cables in an MCB , as long as ccc's are considered, and they are serving similar circuits i.e. two socket radials, two lighting circuits etc.

Would be intersted to know if you'd get pulled for it by your inspector?

 

[Des 56]

Other than saying, it should be only one wire at the mcb
I would be interested to hear the safety reasons why people think it cannot be more

If I was wiring a lighting radial and the lighting was in two opposite directions from the mains board,I would have no hesitation whatsoever taking 2 or more cables from the same mcb

In the above situation,I would say it is not only permissable,but a safer install because of the lower Zs that the branches would give, compared to a run which is doubling back on itself, just to please some obscure reason abot core numbers in an mcb