Two cables connected to mcb

Jay89 · Jul 11, 2017

Evening All

Im sure this will have been discussed at some point (if so please point me to a relevant thread)

I have been to look at some remedial work where a previous inspector has flagged up on multiple circuits 'DBx Cx has two cables in mcb, need separating - C2'

These circuits are either lighting or radial power circuits supplying a small amount of sockets. All suitably rated and with decent R1+R2 readings.

I have never seen this to be worthy of a mention let alone a C2 code, i have spoken to my CPS technical and they said they cant see an issue. Just looking for anyone else's opinion

Thanks in advance!

GMES · Jul 12, 2017

[ElectriciansForums.net] Two cables connected to mcb

...........

ChrisElectrical88 · Jul 12, 2017

I note it on the certificate as for example in conductor sizes 3x1.5 3x1.0 and note that in some cases more than one conductor is terminated into one protective device and this is how it can be noticed.

I know a lot of people who C3 this

ChrisElectrical88 · Jul 12, 2017

Never a C2, someone was after a dist board change.

However if I am changing a CU for other reasons I will ensure there is enough ways to seperate these out.

Also as Westward says, this is normally cause someone has lashed a extra circuit in and can't be arsed

andyb · Jul 12, 2017

westward10 said:
Don't recall suggesting it complied with BS7671 nor is it a personal view. I read Reg 314.4 that each final circuit should be given individual circuit protection that is it which I C3.

So 2 rooms with say 3 sockets in each room,

Each room fed from it's own mcb ok (1 conductor in mcb)
Both rooms wired on the same ring ok (2 conductors in mcb)
Room 1 wired as a radial with room 2 spurred from any socket in room 1 ok (1 conductor in mcb)
Both rooms on same circuit but wired independently back to the same mcb not ok (2 conductors in mcb)

davesparks · Jul 12, 2017

westward10 said:
Final circuit, and yes I will still C3 it lawyers or no lawyers.

You can't just state 'final circuit' without giving a definition for it.
How do you define what constitutes a final circuit and, crucially to this debate,what does not constitute a single final circuit.

At the moment it appears that your definition includes a requirement that a final circuit must only have one conductor at the ocpd.

If there is a 1' piece of cable connected from the ocpd to a JB and then two cables leave that JB to each serve two sockets, is that one circuit or two?

davesparks · Jul 12, 2017

westward10 said:
Don't recall suggesting it complied with BS7671 nor is it a personal view. I read Reg 314.4 that each final circuit should be given individual circuit protection that is it which I C3.

I read the reg exactly the same, it is not that reg which is at debate, it is the definition of a circuit.

If the two cables were not both serving sockets, lets say one feeds sockets and the other a pillar drill, then I would be inclined to agree with you. But when both cables are serving sockets, and if there is no overload as a result of the number of sockets, then I see nothing to comment on.

westward10 · Jul 12, 2017

davesparks said:
You can't just state 'final circuit' without giving a definition for it.
How do you define what constitutes a final circuit and, crucially to this debate,what does not constitute a single final circuit.

At the moment it appears that your definition includes a requirement that a final circuit must only have one conductor at the ocpd.

If there is a 1' piece of cable connected from the ocpd to a JB and then two cables leave that JB to each serve two sockets, is that one circuit or two?

See "definitions".

westward10 · Jul 12, 2017

davesparks said:
I read the reg exactly the same, it is not that reg which is at debate, it is the definition of a circuit.

If the two cables were not both serving sockets, lets say one feeds sockets and the other a pillar drill, then I would be inclined to agree with you. But when both cables are serving sockets, and if there is no overload as a result of the number of sockets, then I see nothing to comment on.

Your latter statement is somewhat contradictory and why you keep harping on about definition of circuit whilst it is the Reg to which I debate I have no idea.

Bobster · Jul 12, 2017

westward10 said:
See "definitions".

"Final Circuit - A circuit connected directly to current using equipment, or to a socket-outlet or socket outlets or other outlet points for the connection of such equipment."

Deleted member 9648 · Jul 12, 2017

As far as I'm concerned if you take two separate lighting circuits on two separate mcb's, and connect them together into one mcb then they become a single circuit. As long as the schedule and board are correctly labelled and identified there is no issue. It may be claimed that this could result in confusion, anyone confused by a correctly identified circuit consisting of two radials linked at the OCPD shouldn't be touching it in the first place.

DPG · Jul 12, 2017

How would you code an RFC which also has a spur fed from the same MCB, ie. at the consumer unit? Refer to on-site guide and and Appendix 15 regs before answering.
The answer is: nothing wrong with it - it's one circuit.

Tuttle · Jul 12, 2017

The On Site Guide (page 71) says you can connect a non-fused spur from a ring final circuit "at the origin of the circuit in the distribution board", which I think would mean three conductors in the MCB and would look like a ring and a radial connected to the same protective device.

If spurring off a ring final inside a consumer unit is allowed then surely having a radial go off in two or more different directions from a consumer unit is ok as well.

What if you add a light or a socket in an under stairs cupboard near the consumer unit, surely you can connect that to an existing lighting or socket circuit in the consumer unit.

Tuttle · Jul 12, 2017

DPG said:
How would you code an RFC which also has a spur fed from the same MCB, ie. at the consumer unit? Refer to on-site guide and and Appendix 15 regs before answering.
The answer is: nothing wrong with it - it's one circuit.

You beat me to it

davesparks · Jul 12, 2017

westward10 said:
Your latter statement is somewhat contradictory and why you keep harping on about definition of circuit whilst it is the Reg to which I debate I have no idea.

What are you debating about the reg? The reg requires that each circuit be fed from a separate way. It does not make any mention of the number of cables which can be connected to an ocpd, merely the number of circuits.
In order to comply with this reg you must have a definition of what a circuit is, otherwise the reg is meaningless.

In definitions a circuit is defined as:
"An assembly of electrical equipment supplied from the same origin and protected against overcurrent by the same protective device(s)"
A final circuit is defined as:
"A circuit connected directly to current-using equipment, or to a socket-outlet or socket-outlets or other outlet points for the connection of such equipment."

Neither of these makes any mention of the number of cables which make up a circuit.

westward10 · Jul 12, 2017

Sounds like there is a lot of lashing on going on.

Two cables connected to mcb

Jay89

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GMES

ChrisElectrical88

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ChrisElectrical88

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andyb

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davesparks

davesparks

westward10

westward10

Bobster

Deleted member 9648

DPG

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Tuttle

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Tuttle

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davesparks

westward10

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