Terminating more than one cable to MCB

[Leah]

Hi All, I've just picked up a small commercial job, it's a large storage warehouse with low energy usage. The main board feeds industrial mated sockets throughout the building (it's a marquee company so these are the fittings they have for their portable appliances and cabling) then a sub board feeds a couple more industrial and the lights and power to a small office and break out room. They are now fitting a small sewing room where one or two people will be working on machines and the subsequent lighting.

The problem I have is that there are no spare ways on the sub board or main, the breakout room has it's own circuit for the sockets and has lights on the same circuit as the office. I'm reluctant to extend any of these existing circuits as there's quite a distance between the breakout and sewing room so volt drop is a concern.
As the sub board is central to these locations when (if ever) is it ok to double up at the MCB? I've always managed to avoid doing this but have come across it frequently in existing installations, in which case I've treated it as one circuit and carried on.

You thoughts would be appreciated.

 

[bigdavs83]

Is there no way a small splitter board can be fitted just a 2 or 3 way one? How is the mains coming into the existing boards? Can Henley blocks be fitted to these to get a feed for a seperate splitter?

 

[Leah]

I'm waiting for the client to confirm but it's possible I'm going to have re-routes the main supply to the sub board to allow a fire exit to be created, so yes Henley blocks and another board would probably be the way to go.

I guess I'd been thinking about this all wrong.

 

[shanky887614]

I'm waiting for the client to confirm but it's possible I'm going to have re-routes the main supply to the sub board to allow a fire exit to be created, so yes Henley blocks and another board would probably be the way to go.

I guess I'd been thinking about this all wrong.

are you allowed according to regs to have a panel made with a buzbar for each line conductor etc and have the connections lugged and bolted to have multiple boards running off it?

bassically a big version of henly block

 

[davesparks]

Do you mean a bussbar chamber?

 

[GMES]

As Dave said is that what you mean if it is then Busbar chambers are still used by many people although personally I prefer to use power/panel boards.

 

[davesparks]

Horses for courses Mr GMES.
panel boards have their place but sometimes you want circuits on BS88s which can push you down the bussbar route.

 

[GMES]

To the Op doubling up an mcb is best avoided if possible but it does happen and I would dare say a lot of members on here have done it, though some may deny it. It usually comes down to common sense,design and often restricted budgets, in theory if both cables are capable of carrying the current with a suitably rated mcb then it should be ok.
The negative side to this is to work on either circuit then the other looses power or during a fault if the mcb trips then you lose both circuits.
Personally if it were me and I had no other option then i would do it as long as long as ccc and mcb rating were correct.
Tin hat firmly attached.

 

[GMES]

Horses for courses Mr GMES.
panel boards have their place but sometimes you want circuits on BS88s which can push you down the bussbar route.

Dave I have no issue with busbar chambers and yes they have their place. My only problem is when i follow either a lazy or cowboy spark who as installed several sub mains without local isolation, you then get a very unhappy customer when you have to inform in that the entire factory as to be shut down if you need to replace/ upgrade a submain db etc.
I am 90% Industrial and see it all the time, at least with an mccb you can isolate individual subs without affecting the rest of the site.

 

[Zebra Stripe]

To the Op doubling up an mcb is best avoided if possible but it does happen and I would dare say a lot of members on here have done it, though some may deny it. It usually comes down to common sense,design and often restricted budgets, in theory if both cables are capable of carrying the current with a suitably rated mcb then it should be ok.
The negative side to this is to work on either circuit then the other looses power or during a fault if the mcb trips then you lose both circuits.
Personally if it were me and I had no other option then i would do it as long as long as ccc and mcb rating were correct.
Tin hat firmly attached.

Why???
Absolutetly no different from junctioning from anywhere else on a circuit, or looping from a light fitting, or spuring from a socket on a radial, infact its a better option as you get easy access to the junction within the DB........by the way its a branch not another circuit when its piggy backed:biggrin5:

"in theory if both cables are capable of carrying the current with a suitably rated mcb then it should be ok". Come on, its not just in theory, its actually fact and it will definately be ok, with a lower volt drop and a lower Zs in relation to looping from the last fitting:winkiss:

 

[GMES]

I was merely saying it is not something i would do from the design stage , my point being if the op doubles up an mcb it may cause an issue if one of the Twigs, sorry branches trips out and the 2nd twig,branch tree shuts down all the pc's etc. this is obviously all guess work.
All I am saying is you need to make sure you that the 2nd branch doesn't cause a major problem if shut down due to a fault on the other branch of the tree, bloody hell I feel like alan tischmarsh or whatever his name is.

 

[Zebra Stripe]

I was merely saying it is not something i would do from the design stage , my point being if the op doubles up an mcb it may cause an issue if one of the Twigs, sorry branches trips out and the 2nd twig,branch tree shuts down all the pc's etc. this is obviously all guess work.
All I am saying is you need to make sure you that the 2nd branch doesn't cause a major problem if shut down due to a fault on the other branch of the tree, bloody hell I feel like alan tischmarsh or whatever his name is.

Why Alan.....titmarch?? I prefere breastmay.....sun comes out and theres honeys everywhere:1eye:

 

[Risteard]

The negative side to this is to work on either circuit then the other looses power or during a fault if the mcb trips then you lose both circuits.

By definition it is only one circuit. In many cases it is the best design because, as said, it reduced voltage drop and circuit impedances.

 

[GMES]

So lets say spark a installs a 20amp circuit for office computers, a year later spark b comes along and doubles the circuit up to supply something on the shop floor, this then trips out knocking all the office pc's off = not an happy customer.
I suppose what I mean is I don't have an issue with doubling it up as long as it is thought about 1st, And I did also say in my post I would be willing to do it.

 

[Zebra Stripe]

I love doubling up or even trebling up, it makes me feel sort of wanton, wild and carefree, a bit like having a threesome, but without the morning after bit, a bit like free falling on a guitar, running wild with the Regs, the worlds my oyster, I can do almost anything.....oh the horror of it all.

Hey but spark B may make the same mistake by spurring from a socket.....there's nothing wrong with doubling or trebling etc in the right scenario

 

[davesparks]

Dave I have no issue with busbar chambers and yes they have their place. My only problem is when i follow either a lazy or cowboy spark who as installed several sub mains without local isolation, you then get a very unhappy customer when you have to inform in that the entire factory as to be shut down if you need to replace/ upgrade a submain db etc.
I am 90% Industrial and see it all the time, at least with an mccb you can isolate individual subs without affecting the rest of the site.

Do you mean sub mains connected straight onto a bussbar? If so I can definately see your point!
You can rest assured I always fit a switchfuse

 

[GMES]

Do you mean sub mains connected straight onto a bussbar? If so I can definately see your point!
You can rest assured I always fit a switchfuse

yes Dave I mean straight onto the busbar it can cause some real problems

 

[ipf]

Do you mean sub mains connected straight onto a bussbar? If so I can definately see your point!
You can rest assured I always fit a switchfuse

I should think so, too.:yesnod:
Got to say, I've never installed, nor come across many busbar systems, without, usually with db's scattered all over the place.

 

[edexlab]

Is it too simple to suggest adding another board next to the existing sub board taking out one circuit then use that way to supply the new board where you'll connect the original removed circuit and your new circuits
I'm assuming you've already assessed the sub main and can get Mcb's to suit the original sub Db

 

[davesparks]

yes Dave I mean straight onto the busbar it can cause some real problems

I can imagine the problems.

Yeeehaaa!