Outside electrics

[phil_ballard]

Sorry if this has been covered before ....

I'm renovating a largish shed (actuallya single stabling unit) of about 14 x 11 feet and want to put electricity in there from the house.

My kitchen has a 4-way CU (Wylex) with wired fuses, one of which (I think) isn't connected to anything. My plan so far is this:

Replace that wire fuse with a Wylex plug-in type MCB (20A? 32A?)
Take that cct via T+E cable to a RCD/switch box on the inside of the kitchen's outside wall

Armoured cable from there (through the wall) to the shed (only a few feet, and not in a place where anyone will dig, but hard to bury the cable 750mm due to drains - can I get away with less?)

terminate the armoured cable in the shed at a garage-type CU (2xMCB plus 1 RCD) and run 2 double sockets from the 16A MCB (T+E in plastic trunking) and neon lights from 6A MCB (T+E surface-clipped to beams).

1 - Have I made any serious errors?
2. Should I change the kitchen CU to a more modern all-MCB/RCD unit? If so, do I need the other switch box in the kitchen? What type?
3. How do I get the armoured cable through the wall and down (it only bends around quite a large radius, obviously)
4. Do I need a sw/fuse or some such in the shed, as well as the garage CU?

Any help much appreciated, sorry I'm a bit of a novice at all this

 

[ban-all-sheds]

Sorry if this has been covered before ....

Countless times - do a search for terms like shed, garage, outside, outbuilding out-building etc...

Replace that wire fuse with a Wylex plug-in type MCB (20A? 32A?)

Not really necessary just because you're taking a supply to the shed. Fuse as good for this as it is for any of the other circuits you have.

Take that cct via T+E cable to a RCD/switch box on the inside of the kitchen's outside wall

Little value in having an RCD at the house end as well, and the potential for nuisance.

Armoured cable from there (through the wall) to the shed (only a few feet, and not in a place where anyone will dig, but hard to bury the cable 750mm due to drains - can I get away with less?)

Yes - the requirement is that it should be deep enough to avoid being damaged by any disturbance of the ground likely to occur. Provided it's reasonably deep (> spade/fork depth) and there's marker tape just below the surface that'll be fine.

Use at least 4mm, pref 6mm SWA - you don't need it now, but who knows about the future, and you don't want to have to install it twice.

terminate the armoured cable in the shed at a garage-type CU (2xMCB plus 1 RCD) and run 2 double sockets from the 16A MCB (T+E in plastic trunking) and neon lights from 6A MCB (T+E surface-clipped to beams).

Remember to use an external gland (CW) in the shed.
Metalclad CU, sockets and switches.
2.5mm for the sockets, 1 or 1.5mm for the lights

1 - Have I made any serious errors?

No. Do you know what type of earthing arrangements your supply has?

2. Should I change the kitchen CU to a more modern all-MCB/RCD unit?

Ideally, but ideally you should do that anyway, not just because of this job,

If so, do I need the other switch box in the kitchen? What type?

Not unless you'll frequently want a way to isolate the shed.

3. How do I get the armoured cable through the wall and down (it only bends around quite a large radius, obviously)

Drill from inside to out with the drill angled downwards. This will avoid the need for a sharp bend and stop water running along the cable into the house.

4. Do I need a sw/fuse or some such in the shed, as well as the garage CU?

No.

Any help much appreciated, sorry I'm a bit of a novice at all this

No need to apologise for that.

 

[securespark]

Ban

Aren't mcb's more sensitive? In some cases, 3036 (rewireable fuses) do not make the grade, as they are a bit slow..

Some schools of thought say it is good practice to have an rcd at the house end protecting the cable (100mA) and another at the outbuilding (30mA) to protect the end user.


As for burying is it 450mm? But you should use a duct (waste pipe?) and warning marker tape - should be deeper than just below surface I'm sure - what if it gets disturbed? I don't mean what will happen if it watches a late-night horror movie, I mean if the tape gets dug up Etc.......

 

[phil_ballard]

Many thanks guys. May I ask why you recommend metal clad sockets? This 'shed' is a decorated and carpeted 'garden room' rather than a workshop, I was hoping to use regular 'interior' style fittings.

 

[ban-all-sheds]

Ban

Aren't mcb's more sensitive? In some cases, 3036 (rewireable fuses) do not make the grade, as they are a bit slow..

Indeed - sorry - I was thinking that often in that position there'd be a switchfuse, but of course they don't use rewireables, do they...

Some schools of thought say it is good practice to have an rcd at the house end protecting the cable (100mA) and another at the outbuilding (30mA) to protect the end user.

Yup, but it's real icing-on-the-cake belt'n'braces stuff, and unless you use a type-S at the house, I still don't think you're guaranteed to have discrimination. I'd agree it's a Good Idea if you're using T/E, but not sure it's necessary with SWA.

As for burying is it 450mm?

That depth rings a bell, and it is more than 1 spade/fork depth.

But you should use a duct (waste pipe?)

Even with SWA?

and warning marker tape - should be deeper than just below surface I'm sure - what if it gets disturbed? I don't mean what will happen if it watches a late-night horror movie, I mean if the tape gets dug up Etc.......

Yo - it's a balancing act - you want it far enough above the cable so that you encounter it before your fork spears the cable, not at the same time, but not so close to the surface that the cat scratches it up.

Many thanks guys. May I ask why you recommend metal clad sockets? This 'shed' is a decorated and carpeted 'garden room' rather than a workshop, I was hoping to use regular 'interior' style fittings.

Sorry - you just said "shed", so I thought you meant workshop/garden store/spider refuge. In your case ordinary accessories will be fine.