Discuss faults, cables spur from mcb. in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

K

KNIPEX

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i did a perodic test today and have opened a right can of worms.

have to say cant switch main switch of in db so

1st circuit, switch of the mcb disconnect the line from the breaker, disconnect the neutral, and its sparks, ok wrong neutral, however while that cable is still out of the n bar and the same phase is out of the mcb the phase cable becomes live, even though its out of the breaker ???? 170v on it.

put the neutral back in, pull out another neutral and the phase cable becomes live again, only way to stop this is switch off another 3 mcb. a right mess.

2nd prob they have spured off the 32a mcb in the db 2.5 to feed sockets down the other end of the building.
a big no think im right in saying that you can only spur once from a socket outlet not from the mcb.

also in another location they have spured of a double s/o to a single s/o in 2.5, that fine. but then spured of the single to feed another single, bushed together so even though its really a double s/o as such as its so close its still been spured off, again NO not allowed

your views on this would be intresting, thanks.

im back there tommorow to continue my investigation, i dread to think what i might find :(
 
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E

eskimo39

  • Thread Starter Thread Starter
  • #2
I think you are allowed to run a spur direct from the MCB to one socket only as long as it is on the same breaker as the ring. If it then went to a second socket you are effectivly spuring off a spur which is not allowed.

I also remember reading that you can only spur the same number of sockes as on the actual circuit and these must be from the back of an existing socket or using a JB.
 
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B

beaver74

  • Thread Starter Thread Starter
  • #3
i think you might find that 2 1g sockets will be ok as total load will only be 26A
but appendix 15 does'nt show this set up
 
H

hughesy

  • Thread Starter Thread Starter
  • #4
i did a perodic test today and have opened a right can of worms.

have to say cant switch main switch of in db so

1st circuit, switch of the mcb disconnect the line from the breaker, disconnect the neutral, and its sparks, ok wrong neutral, however while that cable is still out of the n bar and the same phase is out of the mcb the phase cable becomes live, even though its out of the breaker ???? 170v on it.

put the neutral back in, pull out another neutral and the phase cable becomes live again, only way to stop this is switch off another 3 mcb. a right mess.

2nd prob they have spured off the 32a mcb in the db 2.5 to feed sockets down the other end of the building.
a big no think im right in saying that you can only spur once from a socket outlet not from the mcb.

also in another location they have spured of a double s/o to a single s/o in 2.5, that fine. but then spured of the single to feed another single, bushed together so even though its really a double s/o as such as its so close its still been spured off, again NO not allowed

your views on this would be intresting, thanks.

im back there tommorow to continue my investigation, i dread to think what i might find :(
Hi mate sounds like a right pain this one just wanted to say you can have a spur from the mcb as long as you only have one single or one double its just one more example of where diversity is allowed
 
E

eskimo39

  • Thread Starter Thread Starter
  • #5
In the onsite guide, appendix 8.2.4 it states that in a A1 ring and A2 radial circuit a non-fused spur should feed only 1 single or 1 twin/multiple socket outlet. Such spur should be connected to the circuit at the terminals or a socket-outlet or junction box or at the origin of the circuit in the distribution board.

Hope this helps
 
W

WarrenG

  • Thread Starter Thread Starter
  • #6
I would suggest telling the customer that you are going to have to drop the power untill you can rectify the system. For both yours and their safety.

Unless of course they would like to work on a live board?.........:D
 
K

KNIPEX

  • Thread Starter Thread Starter
  • #7
thanks for the replies guys, very helpful:)

really intrested on your views on the first prob aswell, had anything like this before??etc
 
R

randyrat

  • Thread Starter Thread Starter
  • #8
Sounds like a bad case of shared neutrals to me......
 
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montybaber

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  • #9
We were taught at college (a while ago maybe:)) that spurring from an mcb is perfectly acceptable (only for single outlet though).

why not?
 
1

12345aob

  • Thread Starter Thread Starter
  • #10
We were taught at college (a while ago maybe:)) that spurring from an mcb is perfectly acceptable (only for single outlet though).

why not?
whats the feeling on spuring off the ring 32amp mcb with 2.5 t&e -I've seen this alot and when I see this I think to myself I would not do it.
 
K

KNIPEX

  • Thread Starter Thread Starter
  • #11
here is another one for you, ringmain wired in 4mm2 singles, off 32a mcb, then spured of the socket is 5 double s/o on 4mm2 i know 4mm2 is ok for 32amp however your still spuring of a spur.

have to agree with the above yes neutrals mixed up, however that should cause the line cable to become live when its out of the mcb??
 
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montybaber

  • Thread Starter Thread Starter
  • #12
whats the feeling on spuring off the ring 32amp mcb with 2.5 t&e -I've seen this alot and when I see this I think to myself I would not do it.
just out of interest why not?
 
T

Tapouchoke

  • Thread Starter Thread Starter
  • #13
whats the feeling on spuring off the ring 32amp mcb with 2.5 t&e -I've seen this alot and when I see this I think to myself I would not do it.
od job men and have a go joes who have the therory if the kettle boiles it works :eek:
 
M

montybaber

  • Thread Starter Thread Starter
  • #14
but its fine if the spur is taken from a s/o on the ring?

od job men and have a go joes who have the therory if the kettle boiles it works :eek:
i suppose that is me then
 
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R

randyrat

  • Thread Starter Thread Starter
  • #15
Yup....Unfused spur straight from the ring cct MCB in the dist board.....17th says its fine....
 
O

optician

  • Thread Starter Thread Starter
  • #16
Just so I've got it straight in my head, in this 32amp breaker you have both ends of a ring (2 cables 2.5mm) and then some one has also added a spur, another 2.5mm phase, 3 cables into one breaker?
If this is the case, the ring is protected by the breaker. the spur is not, 27amps max for 2.5mm.
Obviously if you have one socket you can only draw 13amps, two sockets and your close to fire with no chance of the mcb tripping? Am I thinking along the correct lines?
 
H

hughesy

  • Thread Starter Thread Starter
  • #17
It is absolutely fine to spur from the cu see pg 362 in your 17th edition regs if you dont have it maybe its time you updated.read the part about an unfused fuse spur.

Just so I've got it straight in my head, in this 32amp breaker you have both ends of a ring (2 cables 2.5mm) and then some one has also added a spur, another 2.5mm phase, 3 cables into one breaker?
If this is the case, the ring is protected by the breaker. the spur is not, 27amps max for 2.5mm.
Obviously if you have one socket you can only draw 13amps, two sockets and your close to fire with no chance of the mcb tripping? Am I thinking along the correct lines?
this is what they call diversity theres not a great chance it will draw 26a unless you used say 2 heaters and then the regs advise if you were to use electric heating you should wire a radial just for that and not put it on the ring as a ring in thefirst place is designed to share the load, its also the same with ceiling pendants technically th0.5 flex supplying the light is protected by a 5/6 or even a 10 amp fuse and we all know the smallest we can use is a 1.0mm but we also know a light bulb wont use that much current so diversity is applied.
 
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optician

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  • #18
Thanks hughesy, have modified my thinking and read the page.
 
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hughesy

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  • #19
Thanks hughesy, have modified my thinking and read the page.
No problem mate , im new to this site can you tell me how to raise a question , i know how to reply just cant figure out how to post a question. thanks.
 
1

12345aob

  • Thread Starter Thread Starter
  • #20
:)
No problem mate , im new to this site can you tell me how to raise a question , i know how to reply just cant figure out how to post a question. thanks.
when you enter a section- scroll to the botton and click new thread. Hello btw.
 
U

uksel

  • Thread Starter Thread Starter
  • #21
you can have as many sockets in a radial circuit as you want

but any more than one s/o on the radial circuit you create then you need to protect the circuit by using fused spurs.

as for the disconnected phase being 'live' at 170v, this is very unusual. i'd unplug everything from the circuit (incase for some reason paranormal reason there is any abnormal capacitance, voltage sources like batteries there) i'd also disconnect and do some extensive IR tests to see if you've got any sort of leakage. i can say i've not come across anything like this before, except in emergency power/lighting supplies

let us know how you get on with this, i am intrigued
 
K

KNIPEX

  • Thread Starter Thread Starter
  • #22
hi thanks for the comments, it is on a lighting circuit, but the batt in em lighting should have nothing to do with it. this has never proved a prob before or on any other similar circuits in the building.

im looking into it and will let you all know :)
 
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