Distribution circuit question

[LlandrilloSpark]

I'm running a 30 metre length of three core 16mm armour to feed a garage conversion which could have a high loading.
The cable will be run from the external meter box where I will split the meter tails via a Henley
The problem is There is naff all room in the box and I can't fit a switched fuse in there to protect the armour as the main cut out is 100A
Can I put the switched fuse of another suitable protection device at the other end to protect against overload?
Cheers

 

[malcolmsanford]

No you can't you will need to protect that sub main

 

[telectrix]

can yo not fit a switch fuse in a suitable IP65 adaptable box on the wall close to the meter box ?

 

[LlandrilloSpark]

Cheers guys IP 65 it is then

 

[Chr!s]

I'm running a 30 metre length of three core 16mm armour to feed a garage conversion which could have a high loading.
The cable will be run from the external meter box where I will split the meter tails via a Henley
The problem is There is naff all room in the box and I can't fit a switched fuse in there to protect the armour as the main cut out is 100A
Can I put the switched fuse of another suitable protection device at the other end to protect against overload?
Cheers

It is possible to do it that way. There are requirements though.

Regards Chris

 

[Guest123]

I dont think the DNO would be too happy with that arrangement, if they found out of course.:biggrin5:

There wouldn't be anything wrong with what you suggest, further in to an installation but, not at the origin IMO.

 

[Chr!s]

I dont think the DNO would be too happy with that arrangement, if they found out of course.:biggrin5:

There wouldn't be anything wrong with what you suggest, further in to an installation but, not at the origin IMO.

I see no reason for the DNO to have issues. The installation if designed correctly would meet the requirements of BS7671.

Regards Chris

 

[Rockingit]

At least you didn't ask THAT dreaded question........!!

And yes, you need to protect the cable so will have to find some form of additional box to house it in.

 

[Chr!s]

At least you didn't ask THAT dreaded question........!!

And yes, you need to protect the cable so will have to find some form of additional box to house it in.

Are you sure about that ?


Regards Chris

 

[Guest123]

The way I see it, the first 30M of distribution cable would be relying on their service fuse for protection against short circuit, albeit with the added overload protection at the load end.


I'm not saying it's wrong or non compliant but, knowing the DNO as we do they are bound to come across it, see a cable directly connect to their service fuse with no additional protection visible, put 2 & 2 together, make 49 and throw the toys out of the pram.

 

[ackbarthestar]

At least you didn't ask THAT dreaded question........!!

And yes, you need to protect the cable so will have to find some form of additional box to house it in.

Use a 4-core swa and then THAT question is or isn't answered :smiley2:

 

[spark 68]

Just a Thought,

He can put the switch fuse/Isolator within 3M of the origin, suitably labelled of course, I don't know if that will help the Op any, as I cannot see the installation

 

[Chr!s]

The way I see it, the first 30M of distribution cable would be relying on their service fuse for protection against short circuit, albeit with the added overload protection at the load end.

True Lenny, though everyone seems to be happy using the Dnos fuse for short circuit when using standard circuits, after all its the fuse which Annex Za uses to limit Let through and allows the consumer units to be rated higher, also the standard circuits where the Dno's fuse is providing back up protection, the i2t is used for determining CSA.

Do you have discrimination(short circuit) between a 32 amp type B MCB and a 100 amp 1361, what about larger MCB's, on a short the Dno's fuse is now providing short circuit protection to your circuits.


I'm not saying it's wrong or non compliant but, knowing the DNO as we do they are bound to come across it, see a cable directly connect to their service fuse with no additional protection visible, put 2 & 2 together, make 49 and throw the toys out of the pram.

Regards Chris

 

[Guest123]

Just a Thought,

He can put the switch fuse/Isolator within 3M of the origin, I don't know if that will help the Op any, as I cannot see the installation

Absolutely but, the issue was the service head being in an external meter cabinet with no additional room for a switchfuse.

Mounting an additional enclosure adjacent to the meter cabinet has been suggested.

 

[spark 68]

Mounting an additional enclosure adjacent to the meter cabinet has been suggested.

Agreed Lenny, but I was thinking more on the other side of the wall to the DNO's cabinet, ie through the wall

 

[Chr!s]

Well id suggest he utilizes 433.2.2 part (i).

Regards Chris

 

[Guest123]

Agreed Lenny, but I was thinking more on the other side of the wall to the DNO's cabinet, ie through the wall

I took it that he couldn't/didn't want to go internally with it at all....

 

[Guest123]

Well id suggest he utilizes 433.2.2 part (i).

Regards Chris

He could & I'm not disputing that, I mentioned it earlier. The only point I raised was regarding the DNO and their inability to se the wood for the trees. They want (or at least mine do) to see the additional protection within 3M of their service head, end of. They wont be told any different and I just wanted to make the OP aware of it.

BS 7671 isn't the be all & end all.

 

[Chr!s]

He could & I'm not disputing that, I mentioned it earlier. The only point I raised was regarding the DNO and their inability to se the wood for the trees. They want (or at least mine do) to see the additional protection within 3M of their service head, end of. They wont be told any different and I just wanted to make the OP aware of it.

BS 7671 isn't the be all & end all.

Well just remind them of this;

1 Definition Network ESQCR

Consumer’s installations in buildings are not intended to be included in the definition. Such installations should comply with the requirements of BS7671 Requirements for Electrical Installations or those of other relevant standards. Electrical distribution systems on offshore installations are also excluded from the definition, e.g. oil rigs.

So tell them to concentrate on there network and you will concentrate on your installation to the relevant standards.

As for there equipment in a premise then there is also this;

ESQCR

Equipment belonging to distributors and meter operators which is installed on consumers’ premises must be suitable for itspurpose and safe. Examples of such equipment include: cables, meters, distribution boards, isolators and switches.Such equipment must also be electrically protected by fuses, cut-outs or circuit breakers. For safety and technical reasons the protective device should be situated as close as reasonably practicable to the supply terminals. Where flats are supplied by rising mains, duty holders should ensure that all equipment upstream of the supply terminals at each flat benefit from adequate electrical and mechanical protection.
In order to demonstrate compliance with the requirements of regulation 24(1) duty holders should adopt the standards of construction and installation necessary to comply with BS7671 Requirements for Electrical Installations.

Regards Chris

 

[Gazzdid]

Wouldn't that mean the only protection the 16mm would have is the 100A service fuse? I wouldn't even consider that as an option! I would also be doing everything I could to rcd protect the armoured.

 

[spark 68]

I would also be doing everything I could to rcd protect the armoured.

I agree about protecting the submain, but you don't want an RCD at source (Why?) as it would/could trip the whole of the remote installation on an earth fault which is a good 30 M away !, no, RCD's local if required is far better IMO, besides if the RCD was at source would this not contravene the regs wrt circuit segregation ? (314.1).

Unless of course the Installation was TT, and then a time delayed 100mA may be required

 

[telectrix]

why on earth would you want to RCD the SWA?

 

[LlandrilloSpark]

Can of worms lads?

Gazz I'm not wet behind the ears you know I know about the 100A and the 16mm , and why would I RCD a distribution circuit in Armour????

 

[SPARTYKUS]

Wouldn't that mean the only protection the 16mm would have is the 100A service fuse? I wouldn't even consider that as an option! I would also be doing everything I could to rcd protect the armoured.

Gazzdid, please explain your RCD suggestion on the armoured cable....?

 

[DPG]

I would have thought the 100A service fuse protecting the 30M run was a big no-no. If someone puts a spade through the SWA, the supply for the whole house is lost until the DNO comes out? Daz.
PS I'm no expert, so feel free to pull this comment to bits :smiley2:

 

[telectrix]

I would have thought the 100A service fuse protecting the 30M run was a big no-no. If someone puts a spade through the SWA, the supply for the whole house is lost until the DNO comes out? Daz.
PS I'm no expert, so feel free to pull this comment to bits :smiley2:

nothing wrong with your comment. a 60A sw fuse is the answer.

 

[Rockingit]

Hence why you protect the cable using an over-current device.

 

[DPG]

Yep fair enough. Just saw a couple of posts on page 1 that seemed to be saying you don't need the fuse - seemed strange. Daz

 

[Guest123]

Yep fair enough. Just saw a couple of posts on page 1 that seemed to be saying you don't need the fuse - seemed strange. Daz

The question wasn't should we or should we not install it as obviously we should. We were debating on where it should go in relation to the service head.

Overcurrent protection doesn't necessarily have to be at the origin of a circuit, (433.2 refers) but when it comes to the DNO, they are a law unto themselves so in this instance it would be best IMO to place it at the origin.

 

[DPG]

Just trying to get this straight in my head so apologies!

If the overcurrent protection is at the end of the 30M run, the scenario of a spade through the SWA will not result in the fuse blowing, but will blow the service fuse.

I thought if the 60A switch-fuse was protecting the cable it should go at the origin?

Daz

 

[SPARTYKUS]

DPG

I think thats the usual way to do it. As close as poss ( as mentioned within a few metres to keep em quiet)

 

[Guest123]

We're talking two different types of protection here I.e overcurrent & short circuit.

Before we were mainly talking overcurrent protection which ad I said previously can be placed anywhere along the circuit, (433.2.2)

Reliance on the suppliers fuse for short circuit is debateable and IMO in this instance wouldn't be accepted by the DNO should they find out.

Sent from my BlackBerry 9800 using Tapatalk

 

[LlandrilloSpark]

Problem Solved

Got a 100mm x 190mm metal clad enclosure with 80A main switch and 63A MCB, its proteus(CEF) so not the best but it will do the job at origin, im going to have to move the mainswitch slightly in the meter cupboard to fit it in but at its the best i can do

cheers for the input, ive enjoyed reading it all!

 

[Mike Watters]

how will you know if the armour cpc is big enough?

 

[Guest123]

how will you know if the armour cpc is big enough?

He's used a 3c SWA, the armouring is not being used as the CPC due to the 3rd core.

 

[malcolmsanford]

how will you know if the armour cpc is big enough?

View attachment SWA-pvc-xple cpc comparision.pdf

And if he was he may have used the attachment as a guide

 

[Engineer54]

View attachment 10506

And if he was he may have used the attachment as a guide

I never use that table, the one originally posted by Spin in the same ''STICKY THREAD'', is the one to use, and have done for a number of years now. In your link a 16mm SWA cable fails to meet compliance for a XLPE 3 core cable, whereas in the alternative table it DOES comply.... It would also comply in 2 core 16mm form as well!!


Table for 90[SUP]0[/SUP]C Thermosetting SWA cables operating at 70[SUP]0[/SUP]C.

Conductor CSA​	Minimum CSA of SWA to meet 54G​	CSA of armour 2 core​	CSA of armour 3 core​	CSA of armour 4 core​
1.5​	3.4​	16​	17​	18​
2.5​	5.7​	17​	19​	20​
4​	9.0​	19​	21​	23​
6​	13.6​	22​	23​	36​
10​	22.6​	26​	39​	43​
16​	36.1​	41​	44​	49​
25​	36.1​	42​	62​	70​
35​	36.1​	62​	70​	80​
50​	56.4​	68​	78​	90​
70​	79.0​	80​	90​	131​
95​	107.2​	113​	128​	147​
120​	135.3​	(125) ​	141​	206​
150​	169.2​	(138​	201​	230​
185​	208.6​	(191) ​	220​	255​
240​	270.6​	(215) ​	(250)​	289​
300​	338.3​	(235) ​	(269)​	(319)​
400​	451.0​	(265) ​	(304)​	(452)​