Distribution circuit question

[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)​