Two Conductors in one MCB

[JamieK]

Hi Guys

I recently passed my 2391 exams after a 4 week training course and then went on a 3 day Solar PV Course, so I got a lot of theory but zero practical experience which I rate higher than any manual or exam book.

Coming across this forum I hope there are some kind souls out there as I have MANY questions!

Anyway, I entered a property last week and there were two 1.5mm line conductors inserted into a 6A breaker in the CU marked up "downstairs lighting", this struck me as strange as I thought the only time you would see two conductors in one MCB is on a ring final circuit?

It seems there were two radial lighting circuits in the same MCB, I've asked around and dared to enter the mystery that is BS7671 but I cant find out if this is compliant or not - assuming that the Zs on each circuit is compliant with the the max Zs for the breaker I assume this is okay if you need to add a new circuit and there isn't a spare way?

Any input much appreciated.

 

[telectrix]

it's ok to do this, probably there have been extra lights added at some time and there wasn't a spare way. it's obviously better to use 2 ways as the MCB could soon become overloaded and give rise to tripping.

 

[Adam W]

It's a spur. It's fine. Not ideal but technically fine.

 

[Richard]

Nothing wrong with it atall.All the conductos are fused at 6 Amps.

 

[JamieK]

Thank you very much for the response, really appreciate it.

Just a last question though, if I were to conduct a schedule of tests would I do the R1 and R2 on both circuits connected to the same breaker and then record the highest reading?

 

[Adam W]

I would.

 

[JamieK]

Thanks Novus - its confusing because throughout my training I was taught to ensure I record every circuit on the schedule of tests (including any spurs) so its applying all the theory side to what happens in the real world.

I knew I wouldn't have any idea what to do until I actually got out there and started experiencing true scenarios, thanks for the support and feedback.

 

[Adam W]

Anything out of the ordinary is worth noting in the comments on the schedule of tests, eg 'light in hallway spurred from downstairs lighting circuit'

 

[IQ Electrical]

Anything out of the ordinary is worth noting in the comments on the schedule of tests, eg 'light in hallway spurred from downstairs lighting circuit'

If it's a periodic inspection i'd stick to just noting non compliances, there's nothing worse than reading a periodic with personal opinion and 'good practice' issues listed, it tends to detract from the important things.

On the 2 cores in an MCB issue, the 'electrically and mechanically sound' proviso would be the only limiting factor.

You might have 3 x 2.5mm cores at an MCB if a spur is taken from the origin, still compliant.