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Discuss size of main tails in flats in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

P

paul m-c

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hi guys,
i am a domestic installer and i have won a contract to wire 6 flats in a new build and have no experiance of this sized job. my Q. is what cable and size do i use from the meters on ground floor to DB's in flats the max load per flat is less than 80A.

Paul
 
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bcm_spark

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You need to look at the length of the run and other correction factors that may be needed to calculate it. OSG will help.
 
K

kung

  • Thread Starter Thread Starter
  • #3
25mm meter tails used to be 16mm but when i worked for southern electric as a meter engineer we were told have to be 25mm but a good start is look at the incoming to meter.
Regards
Tony.
 
T

trebor

  • Thread Starter Thread Starter
  • #4
hi guys,
i am a domestic installer and i have won a contract to wire 6 flats in a new build and have no experiance of this sized job. my Q. is what cable and size do i use from the meters on ground floor to DB's in flats the max load per flat is less than 80A.

Paul
depends on what protection you are going to use for the risers and how long they are, what is the installation method

the usual method is to install a 16mm 3 core swa which is rated between 64 and 89 amps depending on the method, this will also carry your adequate cpc, if you are fusing at 80 amps at source you will have to go up to 25mm which is rates between 82 -118 amps again depending on the installation method
 
D

daver

  • Thread Starter Thread Starter
  • #5
I have just done a similar job with 8 flats.

You will have to do your calcs with length, diverstity etc. But to reduce cost, you can use 16mm T&E with an additional 6mm CPC. Table 54G

Hope it helps
 
E

electro

  • Thread Starter Thread Starter
  • #6
Hi
You will have to price of 6 KMF (if not already installed) and I would not use SWA as you will need to terminate this in a domestic property, not good.. Its best to use a concentric cable, you will not find the Max current loads for these in the regs you need the manufactures info. If I remember correctly 16mm concentric is rated @ approx 100amps, so you will also need manufacture VD's per metre and measure your proposed runs. Also if your running new submain's you might have to renew the cable containment??

Regards
 
C

coxy

  • Thread Starter Thread Starter
  • #7
Hi Just a thought - can you use a cable that is not listed in regs ???
 
M

maddfridge

  • Thread Starter Thread Starter
  • #8
Hi Just a thought - can you use a cable that is not listed in regs ???
hi there

yes but provided it matches the same level of protection to that stated in bs7671 if you can find it and of course has to bs or en standard just for the fun of it all.:p:p

cheers
 
J

John81

  • Thread Starter Thread Starter
  • #9
hi guys,
i am a domestic installer and i have won a contract to wire 6 flats in a new build and have no experiance of this sized job. my Q. is what cable and size do i use from the meters on ground floor to DB's in flats the max load per flat is less than 80A.

Paul
If im correct you cant use meter tails as the length of the run will be greater than 3 metres. 25mm concentric will be adequate for the job. nasty cable to make off though!!!!!!!!!!!!!!!!!!!
 
W

wattsup

  • Thread Starter Thread Starter
  • #10
concentric cable, I think not

If a riser, just use a 300a busbar top to bottom, tap off to apt. points. It is cheaper than you think

The supply is not down to you, if not a riser, use 25mm 2-core swa to the supply point, also wire a 16mm earth to each propery, no probs, let the supplier design the rest, or ask how they want the supply distributed.

Assuming each property need metering separate, a busbar chamber at incomer and 6 fused isolaters tapped off, then through each meter and onward to each property.

However they want to distribute supply makes no difference, just take a 25mm 2 core and a 16mm earth back to supply, some may even allow a 16mm t&e its worth asking it would save a significant amount of money if they allow, problem is you could only protect with a 63a fuse, which I think would be ample to cover (assuming no electric heating)
 
C

coxy

  • Thread Starter Thread Starter
  • #11
I came across a cable the other day in a block of flats that id never seen before.The line conductor was like normal tails but the neutral conductor was made up of a lot more cores and smaller in diamater,with bare cable as earth Is that the concentric type ???
 
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W

wattsup

  • Thread Starter Thread Starter
  • #12
Consentric is no longer used, concentric is inner single core line, outer core neutral and earth, usually mi and occaisionally swa single core. As a supply cable it can be used but very rare. I have not seen this system used now for 30 years, some older buildings still are connected concentric, some are even connected consumer side consentric, an rcd will not work if so, hence the elf and safety do not like

Debenhams (Sheffield) was wired concentric until about 10/15 years ago. Lighting design showroom insisted lights were protected with rcd, in them days elcb (yes even then)...of course the elcb/rcd would trip. I did tell them it was impossible, 6-months later they rewired the whole store. They didn't even send me a post card -;)

I can tell you, single core pyro's makes your headache...things don't make sense, especially 2-way lights, I had to scratch my head several times when looking at faults in them days, mini earth clamps I thought, err nope mini neutral clamps! ..kin dangerous
 
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C

coxy

  • Thread Starter Thread Starter
  • #13
Hi Wattsup I aggree with you never use this cable !!! I went to one flat that the neutral had burnt out on because not all the strands had been connected in main terminal - some had slipped behind the terminal and were not connected,this cable in my view is very dangerous and would never use it !!!
 
K

kung

  • Thread Starter Thread Starter
  • #14
1st find out what the customer requires as some flats have a meter room also flats norm have a red tip cutout (a link not fuse) and in meter room has cutout panel with all flats black fuses inside. ask electricity supplier what they require as all dbs tails were ungraded to 25mm when i was at southern electric upto 5mths ago as we were told had to be done. from cutout to meter incoming and meter outgoing to db. Although meter outgoing is customers resp we told customer from cutout to meter is ours and 25mm were installed and customers meter outgoing meter to db needed upgrading to 25mm asap.
 
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S

Spudnik

  • Thread Starter Thread Starter
  • #15
Against all advice here, i would say that split concentric cable is fine to use, as long as its suitably terminated and protected throughout its run (RCD if needed).

It also provides the correct size CPC so there is no need to run separate.

Of course, SWA will remove the need for additional protection, however, its an absolute pain to terminate, especially in an insulated CU.

As for DNO, they will dictate what they want from you.

I recently completed 5 flats and i had to run 2 inch ducting to each from the lobby, as they said they will only install meters in individual flats and not in a communal area.
 
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W

wattsup

  • Thread Starter Thread Starter
  • #16
How does consentric cable comply with the latest regs, assumming consumer side, how can an rcd opperate? I don't get it, sorry if I'm a bit slow with new stuff.

A truely consentric cable cannot comply on the consumer side, if it can please explain

They have no choice, you tell them where to install meters, so long as complying with regs, they cannot refuse. They supply the feed, thats all, you can put the meter in the cupboard under shed if you want...they are bull****ting you
 
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S

Spudnik

  • Thread Starter Thread Starter
  • #17
There are 2 different types of concentric cable:

One is for DNO use which is central core and copper 'armour'.

Split concentric is the same, however, around half of the 'armour' is insulated blue with the rest bare for the cpc.

Split con: Split concentric cable to BS7870

Straight concentric is exactly the same with no neutral sheathing.

As for where the meter is put, the SSE will not install meters in bedrooms or kitchens etc, apparently due to access and fire risks etc. Their regs have nothing to do with 7671. They have their own rules.

Not sure what other DNO's do.
 
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W

wattsup

  • Thread Starter Thread Starter
  • #18
That is a bit over the top, but I hope you get my drift, most times it is obvious where to install, sometimes it is not. When descrepincies arrise I always get my way, they put them where I/customer wants them...always, no argument, sometimes it costs more to put in position a) rather than position b) But they cannot dictate.

If they refused to install meters in communal area on one of my jobs I would simply take them to court, they would lose

I ain't going to read forum rules...there is concentric cable and none concentric cable, so you need to make your mind up which, there is no such thing as split concentric although I can appreciate that's what it is called generically.

How can you have a 'split concentric' that in it self is a contradiction

A meter can be fitted wherever you want, so long as it complies with the regs

Assuming the fixing point for meter complies and still they will not fix, sue them take em to court. It will not go that far, I can assure you they will fix
 
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C

coxy

  • Thread Starter Thread Starter
  • #19
If running sub mains I would always use swa,maybe pvc t&e with separate cpc.There are loads of ways to terminate cables.Like I said before I think I would always use cables that I can see the ratings for in the regs.
 
S

Spudnik

  • Thread Starter Thread Starter
  • #20
That is a bit over the top, but I hope you get my drift, most times it is obvious where to install, sometimes it is not. When descrepincies arrise I always get my way, they put them where I/customer wants them...always, no argument, sometimes it costs more to put in position a) rather than position b) But they cannot dictate.

If they refused to install meters in communal area on one of my jobs I would simply take them to court, they would lose

I ain't going to read forum rules...there is concentric cable and none concentric cable, so you need to make your mind up which, there is no such thing as split concentric although I can appreciate that's what it is called generically.

How can you have a 'split concentric' that in it self is a contradiction

A meter can be fitted wherever you want, so long as it complies with the regs

Assuming the fixing point for meter complies and still they will not fix, sue them take em to court. It will not go that far, I can assure you they will fix
Im not entirely sure i understand what you are getting at.

There are 2 different types of concentric cable

One is a straight concentric which has a central core, wrapped in copper 'armour' that is only available for DNO use.

The other is a split concentric, ie the concentric part of the cable is split to form neutral conductors and cpc.

Split con is easier to install and complies fully with BS7671 and i have also confirmed this with tech support, but if you feel happier to run SWA then thats cool.

I know which id rather use.

The DNO have their own regs so they will do what they want and as i said, SSE will only install a meter in suitable locations. Nothing I/we can do about it down here.

As long as i know where its going, ill install accordingly. makes no difference to me.
 
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C

coxy

  • Thread Starter Thread Starter
  • #21
Hi I think because of the termination of this type of cable in consumer units can be dangerous and with so many cowboys about would never reccommend this type of cable !
 
S

Spudnik

  • Thread Starter Thread Starter
  • #22
Hi I think because of the termination of this type of cable in consumer units can be dangerous and with so many cowboys about would never reccommend this type of cable !
Very true indeed, but 25mm SWA i think is just as bad as it is very difficult to work into a CU.

Still, each to his own i suppose.
:)
 
W

wattsup

  • Thread Starter Thread Starter
  • #23
In 30 years I have never ever installed concentic cable, all I have ever done is take them out. That includes domestic, commercial and industrial. In all circumstances I would not use concentric cable. The definitation is blured somewhat, a concentric cable is by defination having a common centre. Which for intense and purpose is not allowed within usual scope of the regs. You cannot distinguish neutral earth within all given circuits, they are all as one.

From a supply it is allowed, but no sub circuits should be allowed, it is a very dangererous road to go down.

At all cost, no matter what bad information you get here should concentric wiring be used on the consumer side

lol, 25mm are shoe laces try terminating 350mm, into a poxy chinese isolator...half the price 10 times the trouble

Chinese say no splitter box needed, bull**** it is complete impossible without splitter, assuming 350mm
 
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S

Spudnik

  • Thread Starter Thread Starter
  • #24
You cannot distinguish neutral earth within all given circuits, they are all as one.

I think the difference between neutral and cpc is fairly obvious:


Split concentric cable to BS7870


But hey, fair enough.

I have and am still using the above with all the right protection and havent had any problems at all.

As for the 350mm, we are talking about a domestic consumer unit, not an industrial or commercial installation.
 
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E

electro

  • Thread Starter Thread Starter
  • #25
Hi


just read your reply, this would only work in a new build and only if the DNO would take reasonability for the riser which they no longer do. The guy said the meters are on the ground floor which the DNO rarely move, they limit there cable above ground to a minimum. You can not install a rising main and just tap off, as the whole block would be tapping off. You are talking about 6 flats to get consumer side power in domestic supply, concentric is fine, you could use double insulated if the containment is very good. Riser and twin earth not practical. Paul are the flats private or public sector?
Regards
 
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