New SWA 3core cable 2.5mm2

[oldbiker]

Hello, free Electrical Advice please.
Before I call a sparkie to upgrade my consumer unit I thought I would bring my outside power up to date. I have a twin+earth 6.0m2 under my floor, running outside to my shed and into a 2 way consumer unit, lights and power.
As far as I can remember this was put under my patio in a length of steel tube and I don't think it was sealed either end.
Because of costs, is it alright to cut the 6.0m off inside my garage and then run SWA 3 core 2.5mm2 under my slabs and into my new workshop?
If so, could I use a metalclad box and blanking plate for the join?
Should the timber workshop consumer box be on a fireproof backing plate?
Would I need another earth inside the workshop?
Thanks for any help.

 

[BruceBanner]

Evening, best to get someone to have a look, to many variables whoever you get in will want to have a look at what's already there & what you are looking at installing on the load side anyway. Sounds like a new build workshop?? Where in southwest are you??

 

[DPG]

You would need to make sure it is OK to drop from 6mm to 2.5mm first But as above, let the sparky have a look and see what is needed.

 

[Deleted member 26818]

Why change it?
Has it stopped working?

 

[ipf]

Is it going to a different position than the shed?
I don't like the thought of a T&E underground in an unsealed steel pipe but who knows in any particular instance. It needs looking at, for various reasons.

 

[TJ Anderson]

Standard shed Q's lol......


What is the electrical load in shed?

How long is the run in metres?

What earthing arrangement do you have?

Is there extraneous conductive parts in shed?

 

[AlmondSauce]

...twin+earth 6.0m2...

I think that's out by a couple of orders of magnitude. Or that's the largest SWA I've ever seen

As above you'd need to get it all checked out and signed off by a spark, but AFAIK there's nothing (strictly speaking) wrong with dropping to 2.5mm2 so long as the correct protection is in place to treat the whole lot as a 2.5mm2 run.

That being said, personally I don't like it as an "enthusiastic" DIY-er down the road could mistakenly assume that he can up-rate the breaker down the line (since from a trivial glance it looks like it's feeding a 6mm2 radial.) It sounds like you're having a significant amount of work done, and unless the distance is huge, I'd say trying to drop down to 2.5mm2 half way is a bit of a bodge / false economy.

If the workshop has no extraneous conductive parts then you can just use the earth supplied from the SWA. If there are extraneous conductive parts, then it gets more complex - but you'd usually have to either TT it, or ensure you've got a 10mm2 earth bonding in that entire run.

 

[oldbiker]

Thanks for all the info guys. I intend to get sparks to do all the connections, just thought I could save him time by running the cables myself. The existing to the shed is still working but needs to be brought upto date.
The load would be 3 or 4, 13 amp sockets and a strip light.
The existing was put in by a spark and the earth from the main consumer box is 6mm.
Distance from mains to workshop is about 20 metres. Just thought I could save some money by using existing inside the house and renew the outside stuff. Its expensive cable.
The new consumer unit will be an MK dual RCD with 10 MCBs.

 

[diditrain]

Where are you putting the new 10 way consumer unit, in the house or shed?

 

[Spoon]

How would changing 6mm T+E installed in metal tubing to 2mm SWA be making the circuit "brought upto date."?
Get the electrician to check out the existing circuit, if you have concerns.
What will you be plugging into these 3 or 4 sockets? The electrician will want to know what you will be using in the shed.

 

[-Matt]

Is it really worth it for saving £20??
2.5 3 core is about £1 per M and 6mm is about £2 per M

 

[oldbiker]

10 way in house.
I just found this "Outside Cables, T&E is however often used for the first part of a submain that makes the journey from the house CU to the point of exit from the building".
They then go on to say about exposure to sunlight......so I have decided to use 6mm SWA from the main CU to the new workshop (shed).
My existing shed has a CU with 2 RCDs, one for the strip light and the other is a 2 double socket ring. Used for DIY tools now and again and a water feature pump.
I will swap this over to the new build but add a couple more sockets. These will run things like power saw, band saw dust extrac unit......
Cost for cable...about £90 so I guess I am looking at about £4-500.
I could possibly do the job myself but I need to get it signed off and I would rather give the money to a spark than the robbing council.
Anyway thanks again for your input, I am seeing a spark tonight, last time I used him he never had the P thing (what ever that is so fingers crossed).

 

[Spoon]

They then go on to say about exposure to sunlight......so I have decided to use 6mm SWA from the main CU to the new workshop (shed).

Ok, so the existing 6mm T+E is not fully in the metal tubing.
Can you not just put capping over the exposed cables bits?

 

[oldbiker]

more trouble than what its worth. Its underground and I can see the entry point under the shed but out of reach. I could take up the floor but to be honest, I think I would rather go the SWA way and then cross over to shed 1 at high level, only 9 inches apart at the roof height. Shed 2 has paving bricks between garage and door of shed so easy to take up and relay. Shed one has 2 foot by 2 foot bedded pavers so not easy to take up.

 

[Spoon]

more trouble than what its worth. Its underground and I can see the entry point under the shed but out of reach. I could take up the floor but to be honest,....

But what about "They then go on to say about exposure to sunlight". Not much sunlight in the above description.
Also, it doesn't need to be armoured.