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Topic Title: how many conductors/circuits in a mcb
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Created On: 05 March 2013 12:30 PM
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 05 March 2013 12:30 PM
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newelectrician

Posts: 13
Joined: 05 July 2011

i stumbled across an old post, but couldnt find a recent post regarding this issue. i wouldnt do it, but

im still learning so, aside from its not the best way to do it, what reg states that you couldnt for example put 2 radial into one MCB.

eg lighting going from the CU in 2 different directions.

im thinking if i came across this on a EICR
 05 March 2013 12:42 PM
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alancapon

Posts: 5699
Joined: 27 December 2005

You need to read the definition of a "Circuit" in Part 2 of the regs, then tell us whether you have one or two circuits fed out of your mcb.

Regards,

Alan.
 05 March 2013 12:42 PM
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Ricicle

Posts: 829
Joined: 23 October 2006

Originally posted by: newelectrician

i stumbled across an old post, but couldnt find a recent post regarding this issue. i wouldnt do it, but



im still learning so, aside from its not the best way to do it, what reg states that you couldnt for example put 2 radial into one MCB.



eg lighting going from the CU in 2 different directions.



im thinking if i came across this on a EICR


One protective device = One circuit !

-------------------------
Empty barrels make the most noise.
 05 March 2013 12:54 PM
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AJJewsbury

Posts: 10964
Joined: 13 August 2003

aside from its not the best way to do it, what reg states that you couldnt for example put 2 radial into one MCB.

eg lighting going from the CU in 2 different directions.

If your DB happened to be in the centre of the area covered by one lighting circuit, then "centre-feeding" that circuit would reduce Zs and v.d. - so might be seen as a good solution!

- Andy.
 05 March 2013 01:03 PM
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Avatar for OMS.
OMS

Posts: 18919
Joined: 23 March 2004

It is a single circuit as described in BS 7671 and is allowable as a simple installation practice.

Personally, I disallow it in the specification along the lines of "The contractor shall............................... single conductor from a protective device at the distribution board linking to each load or loads served by the circuit without theuse of spurs or Tee's as shown on the distribution schematic and services layout drawings. For Ring Final circuits, they shall be arranged as a ring, taking due acount of section length and section loading.................................. No spurs or tees from the ring shall be permitted without the express written permission of the responsible engineer, which may be witheld with good reason."

You get the drift - it's allowable - but I don't like it

Regards

OMS

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Failure is always an option
 05 March 2013 01:14 PM
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Avatar for Parsley.
Parsley

Posts: 884
Joined: 04 November 2004

I have also seen this wiring configuration wrongly coded on numerous EICR's.

Regards
 05 March 2013 01:30 PM
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Avatar for dickllewellyn.
dickllewellyn

Posts: 1131
Joined: 19 March 2010

I'm all for it where necessary, particularly if it saves a junction box somewhere. If the alternative is rakes of cable back and forth to find the next available point to join, I see no problem.

Having said that, for the sake of another way in the consumer unit, if available, why not split the circuit into 2? I guess it depends on the situation, loadings, topology of the circuit etc.

One size fits all? Never!

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Richard (Dick)

"Insert words of wisdom and/or witty pun here"
 05 March 2013 01:40 PM
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daveparry1

Posts: 5886
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I don't like to see more than three conductors in an mcb,

Dave.
 05 March 2013 02:13 PM
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newelectrician

Posts: 13
Joined: 05 July 2011

thanks for all the quick reponses.... as per suggestion above, i looked up definition of 'circuit' in regs and states 'An assembly of electrical equipment supplied from the same origin and protected against overcurrent by the same protective device(s)' therefore in my original example it would have 2 cables from the same origin and protected by same device. As mentioned in my previous post, im all brand new and curious as to which reg would allow/not allow thanks
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