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Topic Title: armoured cable
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Created On: 30 May 2007 10:49 AM
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 30 May 2007 10:49 AM
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krishanc

Posts: 142
Joined: 24 September 2003

Hello

Its only the apprentice here!!

I am wiring my garage and shed to conform with regs. I am going to run a 4mm armoured cable to garage and then via a garage CU to shed.
At the moment, after meter, there is a tail box used to connect 2 different CU's (there was an extention done and a 2-way CU was added). I will not be doing this bit myself as I am not going to remove fuse, but want to understand if my thinking is right.
Would it be more sensible to have a junction box that connect the armoured cable and new tails which in turn connect to the present tail box? Then is would also be easy to run the earth cable to the earth bar from the junction box.

2nd question

At the garage CU, there will be the armoured cable coming from the main tail box via junction box and then also I need to wire armoured cable from the MCB (via RCD) for cable going underground to shed, is it easy to connect a armoured cable to a MCB, I have not done anything with armoured cables before so not sure how easy there to cut and bend and fix!!

regards

krishan
 30 May 2007 11:20 AM
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tj38marlow

Posts: 397
Joined: 20 December 2006

All of your posts indicate you are doing alot of electrical jobs on your house!!!

Must be very big....

Alot of your work woudl be deemed notifiable - but you probably know all about that!!
 30 May 2007 11:39 AM
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AJJewsbury

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Would it be more sensible to have a junction box that connect the armoured cable and new tails which in turn connect to the present tail box?

Your 4mm2 armoured 'sub main' will need protection - the supplier's fuse will be too big to do the job and your main will be too long (>3m) to be exempt.

is it easy to connect a armoured cable to a MCB

The internal cores of SWA aren't all that different from that of T&E (XLPE insulation is a bit tougher to cut and the conductor is usually stranded, even for smaller sizes) so the connection to the MCB itself shouldn't be a problem. The difficulty with SWA usually comes from the armour - you'll need to terminate that into a suitable brass gland and get an earth connection to that.

- Andy.

- Andy.
 30 May 2007 03:09 PM
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krishanc

Posts: 142
Joined: 24 September 2003

Andy, thansk for your response, some comments

Originally posted by: AJJewsbury

[
Your 4mm2 armoured 'sub main' will need protection - the supplier's fuse will be too big to do the job and your main will be too long (>3m) to be exempt.

I do not understand this, are you saying that the 4mm armoured cable needs electrical protection!!!, why? down the line there is a garage CU, are u considering someone cutting through the armoured cable which will be the only time the supplier fuse will become the only (useless) protection to protect anyone, how likely is that!! given that the cable will be layed against the wall exposed, overhead across kitchen units and throught he wall overhead into the garage. I do accept this is however unlikey still a possiblity that some idiot could drill through a visable armoured cable, how would you suggest I protect it?

OR have I misunderstood you?

is it easy to connect a armoured cable to a MCB


The internal cores of SWA aren't all that different from that of T&E (XLPE insulation is a bit tougher to cut and the conductor is usually stranded, even for smaller sizes) so the connection to the MCB itself shouldn't be a problem. The difficulty with SWA usually comes from the armour - you'll need to terminate that into a suitable brass gland and get an earth connection to that.

I intend to use 3-core armoured cable, why would I meet to earth the armoured screen around the cable as well, as long as it is not exposed at all, there surely should not be any need for it. In many applications the glands are used and the screen is used as the earth, since is will have a lower resistance than the 3-core earth wire, but in this case, it can create the possibility of parallel earth paths. I stongely believe in all earthing bonded to one central point. Using the earth core wire within the armoured cable to earth garage and shed back to the main board should be the safest mothod given also that the distance is no more than 30m.

regards

krishan

- Andy.



- Andy.


 30 May 2007 03:16 PM
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krishanc

Posts: 142
Joined: 24 September 2003

Originally posted by: tj38marlow

All of your posts indicate you are doing alot of electrical jobs on your house!!!



Must be very big....



Alot of your work woudl be deemed notifiable - but you probably know all about that!!


Actually, I have not done anything yet, but before starting I am thinking through what needs to occur. I had a local electrical company come in, it was they that suggested instead of having another CU, or replacing the 2-way CU with a 8-way CU, to run armoured cable from the tail box to a garage CU. It is easier to run one cable than 3x twin and earth cables to the garage, but as andy says it does raise another issue (however unlikey) and I do not know if the regs say I need to protect the armoured cable from the tail box to the garage CU.

krishan
 30 May 2007 03:19 PM
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davebarman

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Originally posted by: krishanc

Hello



Its only the apprentice here!!



I am wiring my garage and shed to conform with regs. I am going to run a 4mm armoured cable to garage and then via a garage CU to shed.

At the moment, after meter, there is a tail box used to connect 2 different CU's (there was an extention done and a 2-way CU was added). I will not be doing this bit myself as I am not going to remove fuse, but want to understand if my thinking is right.


Do I understand that there is no single main switch or means of isolation for the
entire installation??

I would stop right their and remain the apprentice until such time as you feel competent enough to carry out such notifible work.

Rergards

Dave

-------------------------
Never knock on Death's door. Ring the doorbell and run like hell, he hates that!
 30 May 2007 03:24 PM
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krishanc

Posts: 142
Joined: 24 September 2003

Originally posted by: davebarman

[
I would stop right their and remain the apprentice until such time as you feel competent enough to carry out such notifible work.



Rergards



Dave


I fully understand your point, I do not intend to connect the new install to the tail box, I am not going to also remove the fuse, yes there is no main swithc, only the main switches in each CU. I intend to do the wiring, testing of everything but the final connection to the supply via the tail box, after local electrical company removes fuse and connect it themselves.

krishan
 30 May 2007 03:26 PM
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krishanc

Posts: 142
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PS.

I have also informed my local council as external wiring comes under building control, they will also inspect prior to switch on.

krishan
 30 May 2007 03:46 PM
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deleted_luggsey99

Posts: 249
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I don't think they will say "switch on" more like do it again!
You don't have the skills for this job so don't do it.
 30 May 2007 04:41 PM
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peterbutt

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Krishan,

Your posts continue to show that you do not have the understanding of the regs to comply with them, ie:

No single means of isolation for installation- if you have a connection block with sets of tails going off to numerous DB's, with no main switch which cuts power to the entire installation, there is the risk that someone will switch off one of the DB's, assume its dead because the circuit they are working on is fed from that DB.
Problem arises when someone has interconnected from one of your other DB's which is still live- Rings get interconnected, spurs get taken off one DB cct and attached to another cct because someone thinks it should be a ring and they only see one cable etc. These things should not happen but DIy'ers thinking they know what they are doing and even cr*p electricians/bathroom fitters etc can introduce problems that you do not know about.
If you know what you are doing and are equipped for Inspection and Test, then you will have an approved Voltage Indicator, a Proving Unit and know how to prove dead, so these risks can be assessed before working, if not, then you may die.


SWA outer sheath has to be earthed via a suitable clamp, that's the regs, you cannot just say I don't think it's necessary! If someone digs down and cuts into your SWA cable, cuts through the SWA protection and gets through to a live conductor, but does not short it to CPC, the protective device will not operate in time and they will fry- the SWA is connected to earth by the banjo clamps to provide a fault path for current if this situation occurs.

The SWA at 4mm csa will need fuse protection to protect the cable from the DB1 to DB2/DB3 whichever it is, if the main switch on the downline DB is rated too high for the cable- ie you may have a 63a RCD main switch, which by type requires 63A+ before it will trip- you have to protect the cable from overheating/overcurrent issues.
Typical main fuse values at suppliers cutout range from 60/80 to 100A. Your 4mm csa will take what maximum current? I'm not looking it up for you! You are operating as designer, installer Inspector and tester- each of these roles requires you to be competent as defined by BS7671, and by Law in the EAW regs 1989. You do not appear- and I do not mean to be disrespectful, just honest- to meet this requirement and so repeat recommendation as made by numerous of us on the forum that you engage the services of a competent professional to do your works.

Peter

edited for typo

-------------------------
Regards,
Peter

Edited: 30 May 2007 at 04:43 PM by peterbutt
 30 May 2007 06:23 PM
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krishanc

Posts: 142
Joined: 24 September 2003

Originally posted by: peterbutt




Your posts continue to show that you do not have the understanding of the regs to comply with them, ie:



No single means of isolation for installation- if you have a connection block with sets of tails going off to numerous DB's, with no main switch which cuts power to the entire installation, there is the risk that someone will switch off one of the DB's, assume its dead because the circuit they are working on is fed from that DB.

Problem arises when someone has interconnected from one of your other DB's which is still live- Rings get interconnected, spurs get taken off one DB cct and attached to another cct because someone thinks it should be a ring and they only see one cable etc. These things should not happen but DIy'ers thinking they know what they are doing and even cr*p electricians/bathroom fitters etc can introduce problems that you do not know about.

I understand the reason, just as many other instances, I seem to lack the understanding of the underlying reasons with the regs. Yes, while I understand totally some parts of the regs, normal cct's, I do lack the knowledge with the more complex issues like protection of an armoured cable when I just thought why do I need to protect an armoured cable that is visable!

If you know what you are doing and are equipped for Inspection and Test, then you will have an approved Voltage Indicator, a Proving Unit and know how to prove dead, so these risks can be assessed before working, if not, then you may die.





SWA outer sheath has to be earthed via a suitable clamp, that's the regs, you cannot just say I don't think it's necessary! If someone digs down and cuts into your SWA cable, cuts through the SWA protection and gets through to a live conductor, but does not short it to CPC, the protective device will not operate in time and they will fry- the SWA is connected to earth by the banjo clamps to provide a fault path for current if this situation occurs.

Again, I now understand why, its really thinking of the most stupidthing people might do and protecting against it, I think I need to take this on board and in future work from that, rather than my view and how I would operate. Eample, I off every thing before I go near changing a light blub even. I don't care if there is 1 or 2 or 3 DB, just off all.

The SWA at 4mm csa will need fuse protection to protect the cable from the DB1 to DB2/DB3 whichever it is, if the main switch on the downline DB is rated too high for the cable- ie you may have a 63a RCD main switch, which by type requires 63A+ before it will trip- you have to protect the cable from overheating/overcurrent issues.

I think you misunderstand, from the meter there is the L & N cables to a tail box which have 2 tails connected in parallel to 2 different CU's. Yes, I do not know what is the main fuse rating, assuming 100A, then my 60A main switch feeding a 30A RCD feeding ring main in garage and raidal to shed, plus 10A lighting in garage via MCB, so yes, I would need to consider fusing the armoured cable just after tail box with a 60A fuse, will need to read about physical boxes that will enable fusing an armoured cable, my orginal idea of running ring and radial in conduct to garage sounds better than the local electrical company's idea!!!

Typical main fuse values at suppliers cutout range from 60/80 to 100A. Your 4mm csa will take what maximum current? I'm not looking it up for you! You are operating as designer, installer Inspector and tester- each of these roles requires you to be competent as defined by BS7671, and by Law in the EAW regs 1989. You do not appear- and I do not mean to be disrespectful, just honest- to meet this requirement and so repeat recommendation as made by numerous of us on the forum that you engage the services of a competent professional to do your works.



Peter

I am applying for my temp. NICEIC registration, I need to undertake some jobs for them to inspect, ideally, I would work on a couple of jobs before doing this anyway, I intend to ring around and see if any local company will engage my services for free but not everyday since I have a job, even though I work from home. I think technically there is no subject I do not understand, yes my regs, understanding is still limited having not worked in the trade, but you have to start somewhere, and for someone who has not done any work in this field I think there is enough understanding with a little help from guys you you to get the job done correctly.

krishan

edited for typo


 30 May 2007 06:37 PM
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alancapon

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Originally posted by: krishanc
. . . . I would need to consider fusing the armoured cable just after tail box with a 60A fuse . . . .


Really? As Peter said, what is the rating of 4mm SWA cable? I'll give you a clue - it is a lot less than 60A.


Regards,

Alan.
 30 May 2007 07:02 PM
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krishanc

Posts: 142
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Originally posted by: alancapon

Originally posted by: krishanc

. . . . I would need to consider fusing the armoured cable just after tail box with a 60A fuse . . . .




Really? As Peter said, what is the rating of 4mm SWA cable? I'll give you a clue - it is a lot less than 60A.



Alan
according to table 4D4A it is 38A

tlc-direct rate their's at 42A

Now, given that the local company that suggested I run armoured cable and put CU in garage and not as I wanted have another tail and replace existing 2-way with 8-way and run ring and lighting with a spur to shed. I am begining to think my method is better, safer than the local electrical company!!!, also, if I run a 4mm armoured cable to garage then technically, I just have a 10/12 meter tail!!!, now is that a sh-- way of doing it !!, having to then put in fuse protection which they did not mention but have been pointed out in this thread!!

krishan

Regards,



Alan.


 30 May 2007 08:13 PM
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alancapon

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Originally posted by: krishanc
according to table 4D4A it is 38A


Ok. You will therefore need ovecurrent protection before the SWA begins. 32A could be appropriate, but you would need to check the Zs to prove that the fuse would operate. You might have to settle for 20A.

if I run a 4mm armoured cable to garage then technically, I just have a 10/12 meter tail


Yes, but with a fuse at the "supply end" in line with the cable rating.


Regards,

Alan.
 30 May 2007 08:33 PM
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kj scott

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krishanc, if you really are the apprentice, keep doing good deals, then work for Alan Sugar, but not as an electrician, he pays more for his apprentice.

-------------------------
http://www.niceic.biz
 30 May 2007 08:55 PM
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krishanc

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Originally posted by: alancapon

[

Ok. You will therefore need ovecurrent protection before the SWA begins. 32A could be appropriate, but you would need to check the Zs to prove that the fuse would operate. You might have to settle for 20A.



if I run a 4mm armoured cable to garage then technically, I just have a 10/12 meter tail




Yes, but with a fuse at the "supply end" in line with the cable rating.



Regards,



Alan.




alan

You have not commented on my view that my orginal plan is better than the local electrical companies, though it would be easier to run one cable.

Ok, given that we need overcurrent protection, ie, that means a CU, yes? why don't I just change the 2 -way (2nd CU next to main one) to a 4-way and run the SWA cable to a another 6-way CU in garage with main breaker, RCD and MCB's. I think this is a messy solution and my orgional idea run the ring and lighting to garage and SWA spur to shed a much better, safer method, what do you say?


regards

krishan
 30 May 2007 08:57 PM
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krishanc

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Originally posted by: kj scott

krishanc, if you really are the apprentice, keep doing good deals, then work for Alan Sugar, but not as an electrician, he pays more for his apprentice.


come on I am only an apprentice in the pratical sense, not in the theory or technical side, only deal I have did was now much is that whore!!!

krishan
 30 May 2007 09:27 PM
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alancapon

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Originally posted by: krishanc
You have not commented on my view that my orginal plan is better than the local electrical companies, though it would be easier to run one cable.


In my opinion, it is neither better or worse. It is an alternative way of achieving your aim. As long as the Zs of the circuits are within the limits of the overcurrent devices for the solutions, then they should be acceptable.


Regards,

Alan.
 30 May 2007 09:46 PM
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peterbutt

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I think you misunderstand, from the meter there is the L & N cables to a tail box which have 2 tails connected in parallel to 2 different CU's. Yes, I do not know what is the main fuse rating, assuming 100A, then my 60A main switch feeding a 30A RCD feeding ring main in garage and raidal to shed, plus 10A lighting in garage via MCB, so yes, I would need to consider fusing the armoured cable just after tail box with a 60A fuse, will need to read about physical boxes that will enable fusing an armoured cable, my orginal idea of running ring and radial in conduct to garage sounds better than the local electrical company's idea!!!


Krishan, I do not think I misunderstood (although it's easy to see how you could be misunderstood as you are really confusing me with your terminology and mess of issues!).

You have tails from your meter going into a henley block (100A connection block).

From this block, tails going to 2 DBs. Problem 1, lack of single means of isolation.
Solution, put inline in the tails, before henley block a double pole 100A isolator.

Problem 2, you want to put in a DB3 on 4mm csa swa, but with no spare capacity.
Solution, since you now have means of isolating installation as you have had the isolator installed by electricity company (as you are not allowed to pull the suppliers fuse, or work live...) you can isolate and replace one of the DBs (1 or 2) with a unit which gives you a spare way, from which you can run your 4mm csa swa to the garage, into DB3.
Better yet, replace DBs 1 and 2 with a unit which has all your ways covered, including the run to the garage. Make sure that you calculate max demand so that you do not overload- you need to know your max fuse rating on supplier cut out, if you overload and blow it, you'll be in trouble. Of course, as you are playing designer, you will be able to calculate max demand, with diversity so that's not a problem.

I intend to ring around and see if any local company will engage my services for free but not everyday since I have a job, even though I work from home. I think technically there is no subject I do not understand, yes my regs, understanding is still limited having not worked in the trade,



What do you do from home? My guess is programmer/web developer but interested to know. UNderstanding technically has not come through in your posts, as you have missed the understanding of why things are as they are.
Have you done any formal training relating to the regs or any electrical work?

All on here happy to contribute, but everyone gets nervous around people who claim to know how to drive, but get in the wrong side of the car.......

-------------------------
Regards,
Peter
 30 May 2007 10:04 PM
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potential

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krishanc
Apart from not knowing the regulations you have demonstrated that you do not understand basic good wiring practice. e.g. 1st arguing about protecting the SWA at all then chosing the wrong level of protection (60A).
It demonstrates to me a fundamental lack of understanding of what you are doing.
There is much more to wiring than being able to read a wiring diagram and guessing what else you need to know by asking questions on here.

You need to be aware that there are many aspects of the work you are thinking of doing that will not be obviously dangerous but could kill someone if you carry out the installation incorrectly.

Get someone who knows what they are doing to do the work.
IET » Wiring and the regulations » armoured cable

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