How many cables can you have in each MCB in the consumer unit?

[HappyHippyDad]

Hello,

Question number 2.

I didn't get shot down in flames with the first question so I feel able to ask another.

How many cables can you have in each MCB in the consumer unit and more importantly why?

This is not in order to try anything myself but I do want to try and have some basic knowledge before I start the domestic installers course.

Thanks..

 

[DNS1]

By the way, I don't want people thinking I'm being argumentative or just being a dick!

I'm genuinely very interested in learning this stuff and hearing what you guys have to say!

 

[wellshocked]

i wouldnt put any emergency stuff like fire alarms onto any other breakers , if there is a fault in the circuit its shared with it will trip out and the fire alrms will lose power and go inot power saver mode, thats when you kind of over step the mark

 

[Des 56]

Not entirely sure to be honest!

I'm just thinking about cable selection and calculations etc.

If you have lighting running on a radial off an MCB, which is also supplying smoke alarms, with both cables in different installation conditions, how would you go about ensuring that the MCB was correct to deal with a fault on either radial? Just use the worst case scenario?

As always

 

[wellshocked]

if your looking for a quick buck and times are hard , i say double up

 

[Deleted member 26818]

That's the problem with thes solid core cables.
Used to be able to get ten in with the old stranded cable, if you gave each a hair cut.

 

[CrazyScozzese]

314.4 Where an installation comprises more than one final circuit, each final circuit shall be connected to a separate way in a distribution board. The wiring of each final circuit shall be electrically separate from that of every other final circuit, so as to prevent the indirect energizing of a final circuit intended to be isolated.

However , a circuit is an assembly of electrical equipment supplied from the same origin and protected against overcurrent by the same protective device(s).

So, clear as mud.

 

[Deleted member 26818]

314.4 Where an installation comprises more than one final circuit, each final circuit shall be connected to a separate way in a distribution board. The wiring of each final circuit shall be electrically separate from that of every other final circuit, so as to prevent the indirect energizing of a final circuit intended to be isolated.

However , a circuit is an assembly of electrical equipment supplied from the same origin and protected against overcurrent by the same protective device(s).

So, clear as mud.

This simply means that it is impossible to have more than one circuit on an MCB.
As soon as you connect another circuit to the MCB they both become the same circuit.

 

[CrazyScozzese]

This simply means that it is impossible to have more than one circuit on an MCB.
As soon as you connect another circuit to the MCB they both become the same circuit.

I just looked this up too, a final circuit is defined as:

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.

Now is does say DIRECTLY, but even with two or more conductors, are they not still directly connected? What do you think?

 

[Deleted member 26818]

Not quite sure what you are getting at?
The 'directly connected to' phrase refers to the other end of the circuit, not the MCB end.

 

[CrazyScozzese]

Am thinking that in conjunction with 'connected to a seperate way', 'a circuit connected directly to current-using equipment', becomes :

a circuit connected directly to current-using equipment ( should be ) connected to a seperate way.

So, does that imply one MCB(fuse), one circuit conductor? Or can an MCB be electrically other than at the origin of a circuit, as it is when other than one conductor is connected, RFC excepted?

I think we should put together a list of grey areas and get the IEE to adjudicate.

 

[CrazyScozzese]

Not quite sure what you are getting at?
The 'directly connected to' phrase refers to the other end of the circuit, not the MCB end.

That is what I was thinking, so however many are connected are still direct.

 

[richy3333]

I found 7 conductors in 1 MCB the last month whilst doing a PIR!

 

[Darkwood]

The correct answer is as many as can safely be fitted and clamped securely as long as the mcb rating dosn't overate any of the cables incl' calcs, so you can have 3 x 1mm cables from a 6 amp lighting breaker as long as the loading etc have all been taken into account, its not bad practice nor does it contravene any reg's...

 

[BillyTheSparks]

I have found 3036 board a 30a circuit with 1 stranded core and one solid core both 2.5mm/equivalent
and in the next 30a circuit the same, each stranded pair was a RFC and each solid was a RFC. So bassically two rings both supplied from 2x 30a rewirable fuses.

Needless to say that was put right straight away!

But back to the point, I think that you can have a spured circuit at the consumer unit just as you would spur from any other outlet of a circuit. As long as it is within the boundaries of the regs and safe

 

[Engineer54]

This situation normally, or more often than not will be on lighting circuits. Some of the older installations, that has been partly modified, or had additions on additions over the years with limited or no available protective device ways in the CU/DB can quite easily end up with a multiple ends being fed from a single device. But as Spin quite rightly stated, these are NOT multiple circuits, it is a SINGLE circuit...


Provided that all normal other circuit parameters are met, i can't really see a problem electrically, certainly not something i would do, certainly not best practice either...lol!!!!!