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..

 

[wallyanker]

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...

I was taught at College that a MCB can be used as an outlet for a spur, so going on that a RFC can have one unfused spur per outlet, the answer has got to be three...

 

[IQ Electrical]

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

Not 'fire alarm systems' but mains smoke detectors are better connected to a regularly used lighting circuit, reason being that the occupants will notice any loss of lighting far sooner.

On the original MCB issue, as long as the connections are mechanically and electrically sound, there is and never has been a 'limit' on cores terminated at a device.

 

[Darkwood]

I was taught at College that a MCB can be used as an outlet for a spur, so going on that a RFC can have one unfused spur per outlet, the answer has got to be three...

My example is lighting circuit and as such is numerous radials from mcb, your relating to a ring main only in a 32amp mcb where its permissible to also fit a third wire in for a spur as well as the ring, as i mentioned before as long as the design load of all the cables in total dosnt exceed the mcb rating and the circuits are individually sounds and installed and calculated correctly then the only thing limiting you is having good sound termination of all conductors associated, and exception to this rule as i believe you've confused the issue is a ring main - where the mcb exceeds the rating of a cable (2.5) that maybe spured but this set-up is in most cases safe as the spur is usually load limited by a plug fuse or spur etc

 

[Marvo]

I like this thread, a very simple question with potentially complex answers.

In the UK does an MCB fulfill the legal requirement of circuit isolation even though it's a single pole device?
If it does, do the UK regs require that all circuits can be individually isolated by means of the MCB?

 

[HappyHippyDad]

Thanks all. Again I didn't expect such a good response.. I'm beginning to like this site!

I thought the answer would be a lot more complicated than just a certain amount of cables, so thanks for all the explanantions. I may actually pass!!

 

[mechelec]

As an example Hager MCB terminal capacity is 35mm^2 flexible wire, so I thinks there is no reason why more than one cable cannot be teminated safely and reliably.

 

[sparky198]

I was on a job just after qualifying back in 2005 and came across a 6A mcb with 4x1.5mm cables in. I phoned my part p scheme provider for advice to see if this situation was acceptable. I was told it is acceptable if loading etc was taken into account but is not best practice. I personnally wouldn't do it but can see the reasons for. As its my name on the certificate its me that's got to answer for my work!

 

[jamie-spark]

Not 'fire alarm systems' but mains smoke detectors are better connected to a regularly used lighting circuit, reason being that the occupants will notice any loss of lighting far sooner.

On the original MCB issue, as long as the connections are mechanically and electrically sound, there is and never has been a 'limit' on cores terminated at a device.

Totaly agree with iq . it states something like this in the OSG.

 

[Jabbajaws]

But .... you can have a spur (radial) from the consumer unit in with a ring final circuit (RFC). So ... two for the ring plus one for the spur makes three in that mcb. Same goes for lighting radials.

I don't suppose you have thr reg number handy for that by any chance do you, ACVC?

 

[Simlec]

I don't suppose you have thr reg number handy for that by any chance do you, ACVC?

is there not a big picture in the back of the reg book!