Multiple Cables in a single circuit breaker

[Darkwood]

Yep ....comes from my ex and a slip-up on my part ... she was a Clarkson so I had her on my phone as 'The Clark of work' as she did nothing but pick fault with anything I did....... hence the ex' context.

 

[Kris_88]

Hi Darkwood, I just went over my last post and I admit it does sound like a hissy fit on my part, though i didn't really intend it to be.

I'm happy to accept corrections when I'm incorrect, it's one of the reasons I joined the forum as I know there's a lot of people on here with a hell of a lot more knowledge than me. In this case though, Ill be honest, I didn't quite understand at the time why it was incorrect to class it as two circuits in one circuit breaker, but as that wasn't part of the original post I wasn't going to question anyone on it as it seemed like a trivial thing. As you said though, wording can make quite difference in some cases, and upon looking up the definition of 'Circuit' in the regs earlier today, I've learned my lesson.

Still new to this site so I need to get used to the forum etiquette I think.

 

[robd]

Hi all, advise needed please (Commercial)

Before I go into detail about why I ask, as this may be a silly question with an easy answer, is there any regulation or reason why two circuits cannot be fed from one circuit breaker providing all cables connected are adequately protected by the device and all loading has been considered?

For example a 10A circuit breaker feeding two circuits, both doing a small amount of lighting in a commercial premises, where it could have easily been wired as one circuit when looking at the load and coverage?

No problem. As a slight tangent, I did an eicr recently, 2 breakers with 4 cables in 1 and 5 in the other. Total of 47 lights on one and 53 on the other, not even accounting for the several chandelier type fittings. Needless to say you couldn't have all the lights (or even close) turned on at once without the breaker tripping and I wouldn't recommend you go as far as 5 cables in 1 mcb!

 

[Crunchie1981]

glad that's cleared up

 

[Knobhead]

No problem. As a slight tangent, I did an eicr recently, 2 breakers with 4 cables in 1 and 5 in the other. Total of 47 lights on one and 53 on the other, not even accounting for the several chandelier type fittings. Needless to say you couldn't have all the lights (or even close) turned on at once without the breaker tripping and I wouldn't recommend you go as far as 5 cables in 1 mcb!

What the hell are you going on about?
2 MCB’s=2 circuits. 1 MCB with 2 out going cables=1 circuit.

Spice Girls - 2 Become 1 - YouTube

 

[BLBelfast]

I never knew this was not allowed. I've always rectified it if there is two sets of conductors. By putting in new MCB or jb. I was taught we had to split it as it could be mistaken for a ring at a later date. This is just good practice then?

 

[Engineer54]

I never knew this was not allowed. I've always rectified it if there is two sets of conductors. By putting in new MCB or jb. I was taught we had to split it as it could be mistaken for a ring at a later date. This is just good practice then?

That's what the circuit description tab's/labels on CU's/DB's are for...

Though i wouldn't say it's best/good practice, it's been a common practice for donkey's years to use an existing domestic lighting circuit OCPD to supply a doorbell transformer and the like. Same with a ring circuit or come to that a radial circuit, the OCPD can be used as point for a local spurred/branched outlet/FCU....

 

[R G]

Thats the thing with solid conductors , you have to be careful that all are secure in the MCBs , I always make sure the ends are doubled over no matter what , Not good practice but thats what you find ...

Taking a look at some MCBs when theres been 3 cables terminated , the rear clamp has actually curved , and when re used for a single or 2 conductors afterwards the clamp is not effective , so you end up replacing the MCB..

 

[telectrix]

:dita:so refit the MCB in a denman's "curve" CU.

 

[driverman]

Hi all, advise needed please (Commercial)

Before I go into detail about why I ask, as this may be a silly question with an easy answer, is there any regulation or reason why two circuits cannot be fed from one circuit breaker providing all cables connected are adequately protected by the device and all loading has been considered?

For example a 10A circuit breaker feeding two circuits, both doing a small amount of lighting in a commercial premises, where it could have easily been wired as one circuit when looking at the load and coverage?

Another way to look at it by a design point of view, is to have both light circuits protected separately by a MCB. That way if 1 MCB operated some lights would remain on by the other circuit.

 

[David M]

Its common sense really, reduce the load on the mcb where possible and increase its life expectancy. Nothing worse than a mcb operating frequently due to being close to its rated limit. Also if you can reduce the number of cables terminated in an individual mcb then you also reduce the likely hood of a bad connection.... how many times have you been to a consumer board and found a loose connection causing arking and such?? In addition the the fewer items connected to an individual mcb the less inconvenient for the user and for an electrician fault finding. On occasion I have terminated multiple cables in one mcb, but only when it is the only option available.

 

[Risteard]

Needless to say you couldn't have all the lights (or even close) turned on at once without the breaker tripping

I'm not excusing how it was connected if you are suggesting that you couldn't get good purchase on the cores in the MCB, but assuming that you are talking about a domestic premises what makes you think that you should be able to switch every light on at the same time? Diversity suggests that this is not something which should happen and therefore may not have been designed for.

In a commercial/industrial premises however there is much more chance of all the lighting being on at the same time.

 

[robd]

I'm not excusing how it was connected if you are suggesting that you couldn't get good purchase on the cores in the MCB, but assuming that you are talking about a domestic premises what makes you think that you should be able to switch every light on at the same time? Diversity suggests that this is not something which should happen and therefore may not have been designed for.

In a commercial/industrial premises however there is much more chance of all the lighting being on at the same time.

I take your point but 40 plus lights on an mcb is a no-no for me, plenty of chandelier type fittings too. Anyway who dragged this up my post was months ago?!

 

[mrloy99]

Try not to get your back up here, you were corrected on a minor point but at the end of the day using the correct terminology and phrasing is the sign of good education and understanding, you would be surprised how a minor error in terminology can be costly if written in a job spec', although not really in your case but consider how many members we have on here that question about garages etc then ask if they can export the PME/TNCS instead of using the term 'extending the equipotential zone' - totally different things.
When you work along side Electrical Clark of Works and/or Electrical designers etc then using incorrect terminology can make you look incompetent and in some cases may lose you work if you're quoting for a contract as such.

All I'm saying is, try not to throw your toys out of the pram because you were corrected, this is one of the benefits of the forum and helps refine your knowledge although I will agree there are 2 ways to correct someone and we do have members that circle like vultures and come in like its their first meal in months.

sorry mate,I couldn't resist correcting your spelling mistakes.

 

[baldsparkies]

With respect,
I think the definition of an electrical circuit needs to be clarified before anyone can justify calling two separate circuits a single circuit.
If I am reading comments correctly,
2 independently wired circuits are being supplied from a single mcb.
That doesn't make them 1 circuit.
Surely if there are 2 feeds and 2 returns connected across, and supplying different loads.
They are inherently 2 circuits ??
That would be how I see it anyway, but am open to being convinced otherwise. :icon12:

Sorry should explain my reference is with regards to the OP's first post.
I feel his 2 circuit description on 1 mcb is an accurate description.