garden shed supply

[clematis432]

I ran a supply to my garden shed several years ago, but now after browsing this forum for a couple of years, realise how little I know of installation methods.
Due to my CU being the opposite side of the house from my garden shed, I took my supply to shed from the downstairs ring main. I used a 3 core 4mm SWA cable using third core as earth and bonding this also to the cable armouring. I connected the SWA cable to ring main circuit under floorboards using a metal JB and the cable then goes underground (approx 500mm depth) for 15 mts to shed. The ring main is protected in the house CU by a 32A mcb and a RCD The shed has a double pole isolator feeding a 6A mcb for lights and a 20A mcb for one double socket.
I know a separate supply from CU with dedicated protection would have been better practice, but would like to ask, if the installation is within Regs and suitably protected.
I am an ex maintenance electrician with a decent knowledge of electrical theory but little experience of installation methods.

 

[Ducksy]

I don't think that's right as your distribution circuit to the shed should be on its own way in the distribution board and a circuit cable csa must stay same size throughout 2.5mm to 4mm is not ok.

 

[Ducksy]

Have you got a spare way in you DB if so terminate the swa to a metal junction box and run 4mm t&e back to board on its own fuse.....all this work would require a EIC electrical installation certificate tho

EDIT this circuit must be RCD protected

 

[clematis432]

Have you got a spare way in you DB if so terminate the swa to a metal junction box and run t&e back to board on its own fuse.....all this work would require a EIC electrical installation certificate tho

I have got a spare way in the house DB Ducksy, it,s just such a job to get from the back of my house to the DB at the front, that,s why I would only do it if the original install is unsafe or flouting the Regs.

 

[Engineer54]

I don't think that's right as your distribution circuit to the shed should be on its own way in the distribution board and a circuit cable csa must stay same size throughout 2.5mm to 4mm is not ok.

Where did you get those little gems from then?? lol!!

 

[Engineer54]

I have got a spare way in the house DB Ducksy, it,s just such a job to get from the back of my house to the DB at the front, that,s why I would only do it if the original install is unsafe or flouting the Regs.

Your basically OK clematis... Not an ideal installation, but nothing wrong or against the Reg's, coming off the ring main.

 

[Ducksy]

I don't think that's right as your distribution circuit to the shed should be on its own way in the distribution board and a circuit cable csa must stay same size throughout 2.5mm to 4mm is not ok.

Where did you get those little gems from then?? lol!!

What little jems are you saying you can feed a garage db via a ring main and you can have different size cable on one circuit ? Sorry if my advise was poor

 

[decolad69]

Your basically OK clematis... Not an ideal installation, but nothing wrong or against the Reg's, coming off the ring main.[

Agreed.

 

[Engineer54]

What little jems are you saying you can feed a garage db via a ring main and you can have different size cable on one circuit ? Sorry if my advise was poor

Yes you can!! There is NO requirement to run a shed supply only from the CU on a separate circuit. Granted this would be the ideal arrangement.

We are talking about a spur from a ring here, with a cable that complies with the protective device provided!! Different if the OP had used 2.5mm, then he would need to have fed the shed from a FCU on the ring....

 

[Ducksy]

I guess any cable size can be used as long as the CCC is above the load

If that's the case could he have used 2.5 swa instead of 4mm

Thanks for setting me straight eng

 

[clematis432]

I guess any cable size can be used as long as the CCC is above the load

If that's the case could he have used 2.5 swa instead of 4mm

Thanks for setting me straight eng

I originally, if I remember, was going to use 2.5mm as I had some, but calculated it was just too small.

 

[Ducksy]

I guess any cable size can be used as long as the CCC is above the load

If that's the case could he have used 2.5 swa instead of 4mm

Thanks for setting me straight eng

I originally, if I remember, was going to use 2.5mm as I had some, but calculated it was just too small.

Of corse because its a ring the shed feed is a radial i think ccc for 4mm clipped direct is 37amps so well with in size.

 

[Engineer54]

I originally, if I remember, was going to use 2.5mm as I had some, but calculated it was just too small.

Just as well then...lol!! Not sure why you used a 20A MCB for the socket outlet though, a 16A would have better suited. Even a 10A if your just using it for occasional power for tools etc!!

Or is this your naughty room where you get sent by the Mrs, and you need heating, TV, Beer fridge, etc, etc!! lol!!!

 

[clematis432]

Just as well then...lol!! Not sure why you used a 20A MCB for the socket outlet though, a 16A would have better suited. Even a 10A if your just using it for occasional power for tools etc!!

Or is this your naughty room where you get sent by the Mrs, and you need heating, TV, Beer fridge, etc, etc!! lol!!!

Just checked my shed local protection again and not trusted my memory, and it,s a C2A for light and C10A for socket(must have been what I blagged from work) The socket is for a tumble drier and yes a summer beer fridge if the Scottish summer actually gets warm enough !

 

[Engineer54]

Just checked my shed local protection again and not trusted my memory, and it,s a C2A for light and C10A for socket(must have been what I blagged from work) The socket is for a tumble drier and yes a summer beer fridge if the Scottish summer actually gets warm enough !

If these MCB's are both Type C, then i would check your Zs complies to be on the safe side!!