CU 10m from incoming box - new dwelling

[Samamer]

A plastic conduit is laid under the floor ready for a cable. I want to use 25mm tails rather than armoured. Previously I’ve fitted 100amp SP&N fused switch with 25mm armoured but they are tight to make off in the mains electrical meter box and some providers don’t want you in there box! If you had the main switch as an RCD could you run tails rather than armoured?

 

[DPG]

Is this a feed to a consumer unit? You don't want an upfront 30mA RCD.

 

[pc1966]

Without a 30mA RCD you need to meet the protection of > 50mm, etc. Having a 30mA RCD up-front is a whole world of pain you want to avoid on nuisance trips.

You could use 25mm SWA glanded to steel trunking in the fused-switch area to bring the conductors in as if they were tails, with earth to the trunking outside of the switch if that helps.

Or cover the plastic trunking run with earthed steel plate as a barrier?

 

[Samamer]

Thank you for your advice. If the meter tails went straight out the back of the meter box, down the cavity, under a block and beam floor and then up the wall to the consumer unit in metal trunking, that would suffice correct? >50mm as in the cavity and under block and beam and then mechanical protection coming up the wall to the consumer unit?

 

[Leesparkykent]

Thats a big load for a dwelling to require 25mm?

 

[Rockingit]

Thank you for your advice. If the meter tails went straight out the back of the meter box, down the cavity, under a block and beam floor and then up the wall to the consumer unit in metal trunking, that would suffice correct? >50mm as in the cavity and under block and beam and then mechanical protection coming up the wall to the consumer unit?

Generally frowned upon to drop cables down cavities

 

[Samamer]

Thats a big load for a dwelling to require 25mm?

It’s a 12m run in plastic conduit under the floor, allowing for 5% VD. DNO 100a, I will fit 80a SP&N switched fuse. I thought it would be min. 25mm? Would I get away with 16mm? It’s much better to work with in a domestic setting. It is only a 2 bed house with low load

I presume this is the best way unless there’s a better way?

 

[suffolkspark]

16mm 3core armoured. Do it properly.

 

[Rockingit]

You could run 16mm T&E out of a KMF

 

[Samamer]

My initial thoughts were 16mm armoured but the calcs bring it in at 25mm armoured buried in coduit, does in not? 100a DNO, Protected by an 80a switched fuse before heading to the consumer unit.

25mm armoured is just a pain in a domestic setting with tight bends, so was looking for an alternative. I’m just a little confused how 16mm meets the cable calculations for VD

 

[Wilko]

Just my 20p - a 10m path travelling hidden through various domestic building fabrics should not be done in tails. Reason - we don’t want the upfront RCD and by the time we’ve provided equivalent protection to SWA we probably should simply have used SWA.

 

[suffolkspark]

My initial thoughts were 16mm armoured but the calcs bring it in at 25mm armoured buried in coduit, does in not? 100a DNO, Protected by an 80a switched fuse before heading to the consumer unit.

25mm armoured is just a pain in a domestic setting with tight bends, so was looking for an alternative. I’m just a little confused how 16mm meets the cable calculations for VD

Why would you put armoured in conduit?

 

[Samamer]

Thank you for the advice all. I will use armoured.

I meant ducting and for future proofing. If you ever wanted to pull something through in the future as it’s under a block and beam floor.

I’m still not sure how people are working out 16mm SWA the calcs come out at 25mm surely? Unless anyone can explain otherwise?

 

[HappyHippyDad]

Thank you for the advice all. I will use armoured.

I meant ducting and for future proofing. If you ever wanted to pull something through in the future as it’s under a block and beam floor.

I’m still not sure how people are working out 16mm SWA the calcs come out at 25mm surely? Unless anyone can explain otherwise?

Could you show your VD calls?
16mm has a CCC of 87A ref method c.
VD = 2.8 x 80A x 12m / 1000 = 2.69V (to the consumer unit).