16mm to new board

[leekemp85]

I have wired a 16mm to supply a new board for a extension I have been told I cant use a 30ma rcd to protect this cable due to discrimination with the rcds on the new board. I think I will have to chop the cable in to 50mm of the wall, would this be the only way to get around the problem.

 

[sparks1234]

Why not put it onto a time delay?

or 100ma RCD

 

[leekemp85]

I thought 100ma would be ok but elesca told me not

 

[Smugley]

Or surface mount it? Or use SWA instead?

 

[saveloy]

Be careful when sinking a cable 50mm into a wall as you can seriously undermine the structural integrity of the wall!

Vertical chase depth can be no more than 1/3 of wall thickness (or thickness of leaf in cavity wall) ie wall or leaf must be min 150mm thick. ( unlikely in a cavity wall)

Horizontal chases can be no more than 1/6 thickness of wall. Ie wall or leaf must be min 300mm thick. (No chance on a cavity wall.)

 

[sparks1234]

Explain a little as to how this supply is going in. is it armour or T & E or ??, is it chased in etc etc

 

[leekemp85]

chased in the wall 16mm twin, its a old cottage the walls are around 700 think so I might chase it in to 50mm, only around two meters up a wall then I managed to get it through to the extention for the new board.

should you use a switch fuse for or sub boards or a 63 amp mcb (RCD depending how its wired)

 

[Smugley]

Is chasing it in below 50mm easier than adding earthed metallic conduit for that run?

 

[leekemp85]

its would have to be a large chase for a conduit to take a 16mm twin
I think i will get the grinder out

 

[The Truth]

is the 16mm t/e currently buried or chased in at any point? or is it just running through the floor and appearing at both ends on the surface? if its not chased in anywhere currently then you dont need the 30mA RCD to protect the submain. just use normal MCB at supply end or time delayed RCD if its a earth rod system.

 

[beaver74]

Why not put it onto a time delay?

or 100ma RCD

cant put it on a time delay as it is flushed in it will have to be on a 30mA unless in earthed conduit or the like

 

[mrloy99]

I have wired a 16mm to supply a new board for a extension I have been told I cant use a 30ma rcd to protect this cable due to discrimination with the rcds on the new board. I think I will have to chop the cable in to 50mm of the wall, would this be the only way to get around the problem.

LOL>>
(I think however I would have used split concentric cable,as its got full sized 16mm earth and I think it would probably not need 30ma protection)You don't mention if the origional installation is TT orTNcs

 

[mazdaman]

Why not put it onto a time delay?

or 100ma RCD

This would not comply. Cables buried in walls not mechanical protected need to be 30mA <40ms as for personnel protection not 100mA or with time lag as for equipment protection.

see regs
415.1.1
522.6.6
522.6.7

LOL>>
(I think however I would have used split concentric cable,as its got full sized 16mm earth and I think it would probably not need 30ma protection)You don't mention if the origional installation is TT orTNcs

Split concentric will need 30mA ,40mS RCD if sunk into wall as the neutral conductor will remain unprotected.

SWA, earthed conduit or surface install is the answer.

 

[The Truth]

LOL>>
(I think however I would have used split concentric cable,as its got full sized 16mm earth and I think it would probably not need 30ma protection)You don't mention if the origional installation is TT orTNcs

excuse me for saying.....but split concentric?? has anyone ever actually bought and used that for a job?! i dont think i could even buy it if i wanted too! was thinking it was exclusively used by supply authority

This would not comply. Cables buried in walls not mechanical protected need to be 30mA <40ms as for personnel protection not 100mA or with time lag as for equipment protection.

see regs
415.1.1
522.6.6
522.6.7



Split concentric will need 30mA ,40mS RCD if sunk into wall as the neutral conductor will remain unprotected.

SWA, earthed conduit or surface install is the answer.

split concentric comes in 2 and 3 core..the latter has the separate neutral protected.

i had some professional in the wholesaler last week ( who was fresh off the 17th edition course ) preaching to me that if you used a twin / earth for a submain..it had to have a 30mA RCD at both ends!! WTF

he said...'if you look in the book i think you will find.....'

i was waiting for the ' ive been doing this for x number of years.......'

make up your own rules part P soldiers everyone else is

 

[mrloy99]

excuse me for saying.....but split concentric?? has anyone ever actually bought and used that for a job?! i dont think i could even buy it if i wanted too! was thinking it was exclusively used by supply authority.
We've been using it for submains for the last 15years.The stuff the supply authorities use is a bit different..usually aluminium.The stuff we use is copper.I use it for showers too though the 10mm stuff is harder to get.Also comes in 4mm..and is often used for street lighting.Far easier to use than t&e and very little cost difference.Your local cef probably do it,mine does.....but as far as the 30ma bit goes I think it could be argued that it has an earthed metallic screen does it not? Though it would probably best to consult the powers that be to confirm.What about surface clipped?

 

[The Truth]

fair enough i will look out for that cable cheers.

ref the earthed metallic screen..... actually i have just seen a pic of the cable and the cpc dosent tottally surround the other cores like the armor in an SWA cable so in effect the cable wouldn't fall into that category which is a shame.

 

[trix]

With only the information given;
If you're adament with the choice of cabe, routing and chasing, why not intoduce a 30ma rcd at source, and a none rcd distribution board on load side.
That way there's no requirment to incorage you to risk demolishing an otherwise perfect construction, you cover the 16mm and the sub-circuits....

 

[mrloy99]

With only the information given;
If you're adament with the choice of cabe, routing and chasing, why not intoduce a 30ma rcd at source, and a none rcd distribution board on load side.
That way there's no requirment to incorage you to risk demolishing an otherwise perfect construction, you cover the 16mm and the sub-circuits....

Sounds sensable.