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..

 

[trev]

my record is 6 2.5's in 1 MCB. :ban:

Bloody lightweight

 

[Richard Burns]

Damn you beat me, I just saw a CU today with five 1mm in a lighting circuit, four 1 mm in another lighting, couple of normal rings, two 2.5 and one 4mm in another and a 6mm SWA and a 2.5 in another. All unlabelled!

Murdoch's post also reminded me of two rings joined into one ring but different ends from different cables joined together and two CPCs joined then linked to MET with the other two CPCs in another slot, rats nest wiring nightmare to identify and test.

 

[DNS1]

Are we talking about what is permitted or what has been done by people with hats, spurs and revolvers?

 

[wellshocked]

in theory if you add the 2.5 and 2.5 mm cable together you can get 5mm cable which means you can also add a light onto the circuit with the spare 1mm

 

[wellshocked]

:single ****:

 

[GLENNSPARK]

Nope I dont buy that chestnut sorry

no..nor do i Des.....i mean what if you have a situation where ,say the CUs in a cellar head....and you need a lamp at the top of the cellar stairs...what then?....run about 5 meters from the nearest point on the downstairs lighting circuit?....or take a feed from the MCB to that 1 point in the cellar head...about2 meters from the board....as its still coming from the same MCB....you will still acheave everything you need...disconnection times,..safe iso etc.....cant see a problem with it.....

 

[wellshocked]

no..nor do i Des.....i mean what if you have a situation where ,say the CUs in a cellar head....and you need a lamp at the top of the cellar stairs...what then?....run about 5 meters from the nearest point on the downstairs lighting circuit?....or take a feed from the MCB to that 1 point in the cellar head...about2 meters from the board....as its still coming from the same MCB....you will still acheave everything you need...disconnection times,..safe iso etc.....cant see a problem with it.....

what would happen if you had no spares left in the board , you coulnt try and give the person a quote for a new board install just to put in one extra light they would tell you where to go, and what if the last point werent accsesible

 

[trev]

couldnt you then just upgrade to a 10 amp breaker

Why? if the extra load on that circuit is going to be 3 tenths of bugger all?

 

[wellshocked]

Why? if the extra load on that circuit is going to be 3 tenths of bugger all?

depends on what other lights they got on that breaker, if it was just normal ceiling roses i would just leave it , if they had downlights in every room i would change it

 

[DNS1]

If you upgraded the breaker couldn't it end up being incompatible with the original part of the circuit?

 

[Des 56]

Please explain mate, I'm only new! :book:

An example
Upstairs lighting fed from 6 amp mcb,smoke alarms to be installed
I prefer them to be fed from a local lighting circuit,do I try and find a convenient light to try and get to for that connection, or slap it on the up lighting mcb
Now dont say find a lighting point,because I also prefer them to be fed direct from source so that some numpty changing a fitting wont ditch my smoke alarm connection

Lights that I want on one circuit have lights to the left hand side of the house and lights to the right
To avoid having more than one cable in the mcb,I need to feed the circuit for perhaps 2 or 3 times the length

That is reason enough for me,now your turn for only one

 

[GLENNSPARK]

what would happen if you had no spares left in the board , you coulnt try and give the person a quote for a new board install just to put in one extra light they would tell you where to go, and what if the last point werent accsesible

hence my post at #21.

 

[GLENNSPARK]

If you upgraded the breaker couldn't it end up being incompatible with the original part of the circuit?

so would you just "upgrade the breaker" without performing essential tests.....such as a Zs?.....how would you know that you would still need disconnection times?

 

[wellshocked]

If you upgraded the breaker couldn't it end up being incompatible with the original part of the circuit?

you can use either a 6 amp or 10 amp for lighting, it just different loadings on each breaker, if you went higher it could become incompatible, I.E wouldnt trip out and would fry the cable

 

[DNS1]

That is reason enough for me,now your turn for only one

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?