Two radials from one 20A mcb

[Matesrates]

I have been asked to add a double socket in or right next to the board cupboard.
There is no spare ways and the house sockets are wired as two radials.
There is however a circuit for an electric fire wired in 2.5 T+E from a 20a mcb, i was under the impression there is only to be one cable/circuit per mcb apart from ring circuits.
Can i wire this new socket from this mcb? The socket will only be used for a hoover and maybe a table lamp.

Thanks

 

[Plonker 3]

I don't see anything wrong with my first post in this thread, call it a spur or whatever you want, but if you have two radials with say a dousen sockets on each, they ate two circuits in my mind.

Read the definiton in the BYB forcircuit and you will find you are incorrect

 

[davesparks]

I don't see anything wrong with my first post in this thread, call it a spur or whatever you want, but if you have two radials with say a dousen sockets on each, they ate two circuits in my mind.

A circuit is defined in bs7671 as being an assembly of electrical equipment supplied from a single OCPD (or OCPDs in the case of tp fuses etc)
So a circuit as defined by the regulations incorporates all outgoing conductors connected to a single OCPD.

 

[davesparks]

I can't see anything wrong with your first post, maybe Dave being awkward (first for everything)

Cant see why shanksy has quoted me?

As per the regulations a circuit is defined by the OCPD, so all outgoing conductors from a single OCPD are a single circuit.

 

[malcolmsanford]

I have been asked to add a double socket in or right next to the board cupboard.
There is no spare ways and the house sockets are wired as two radials.
There is however a circuit for an electric fire wired in 2.5 T+E from a 20a mcb, i was under the impression there is only to be one cable/circuit per mcb apart from ring circuits.
Can i wire this new socket from this mcb? The socket will only be used for a hoover and maybe a table lamp.

Thanks

What you are proposing in reality here is using the MCB as a "Junction point/box" which is fine in reality if the circuit remains fundamentally a power circuit.

You should though never say spur of a light from a power circuit, even if you use the correct size cable, though there is nothing basically wrong with doing that if you wish to, it does come under in my opinion "bad practice", and could lead to problems in the future with other electricians basically trying to work out what you have done.

As for should you do what your proposing again in my opinion I wouldn't want to do it unless there really was no other way

• How many cables can we shove into an MCB. I say 2 maximum, sparks number 2 says no you can get 3 in easy, sparks number 3 say rubbish 4 1mm a piece of cake, and it could go on and on.

• That heater is it over 2kw ? I know chapter 15 is just informative, but I think as it is in the book it should always be considered. If it is then the spark before you designed perhaps say that the heater should be on it's own circuit for this reason, your going to change that and so are you making the installation less safe, that is for you to decide.

• A spark following you will see 2 x 2.5mm cables for a power circuit in one MCB, that will automatically put into his mind a ring final, and he will work or test accordingly. It just adds to confusion and confusion and electrics is not a good mix.

 

[uksparks]

I accept that it's officially one circuit but you know what the OP what getting at.

 

[malcolmsanford]

1 OCPD is 1 circuit totally agree and everything coming out of that OCPD is the circuit.

So lets say you 4 lights in 2.5mm, a couple of sockets in 2.5mm. a bell transformer in 2.5mm, all backed up with a 20amp MCB/RCBO does the circuit comply?

 

[baldsparkies]

Nice thread,
Starts as a mole hill, and now its Everest.
Could only be a group of housebashers with chinese whispers, and a regs book, thrown in for good measure lol xx