Outside Electrics

[oxford_30]

Hi I am wondering the best way to put electric in my shed, it is about 20ft away from my house, I was considering just running a cable from an unused socket in my kitchen to an outside junction box, then armoured cable from there to the shed into an ordinary 2 plug socket. However I would also like to install garden and decking lights. any suggestions would be a great help.
Thanks
Colin

 

[numpty with a crowbar]

Ok - not even a knowledgable amature but here's my take: -

I was considering just running a cable from an unused socket in my kitchen to an outside junction box, then armoured cable from there to the shed into an ordinary 2 plug socket.

This is known as a "fudge to get round part P" and isn't safe (but may become more common as people wake up to the limitations that P places on you - in the days before P you could have done it properly, got a spark or someone with the knowledge to rig you up some SWA back to your ditribution board, put it on an RCD, and you'd be sorted. Nowadays, thanks to Hull finest MP (right hon John Leslie Prescott and the muppets at OOTDPM), you have to either bodge as you suggested (which frankly could be a shortcut to electrcution), or pay a spark to install and certify.

Frankly if you're doing shed / lights / outtside power it might be advisable to find a friendly spark, do the donkey work of laying SWA in trench / laying other cables to save cash. Then getting a spark to inspect cables, hook it all up and certify

Someone with the proper knowledge will doubtless advise more specifics - but wouldn't bother with the bodge - not worth the faff to be honest

 

[dazzle25]

hi just reading your question, im a qualified electrician of 9 years, i would personally(depending on what is going in shed) i would run a armoued cable from your fuse board under the ground to a fuse board in the shed, and then run out of that fuse board to sockets,lights etc.

 

[Spark123]

The socket in the shed should be RCD protected as it is almost certainly going to be used to supply equipment outdoors.
It depends on what you are wanting to be run and future requirements as to what size supply you need to install.
If you are just wanting a basic setup for a light and mower and it is never likely to need to be upgraded, it may be more viable to run a 16A/20A radial from the CU or a fused spur from the ring out to the shed in SWA, the SWA terminating in a double pole isolator switch, then to a RCD socket outlet and a 3A switched fused spur (or separate switch and fused spur) for lights.
Please can you confirm which type of supply you have and if you have any other services in the shed i.e. water? Also if you are likely to ever want a larger supply in or around the shed in the future?
I take it you are already aware of part p (sorry ) and will either employ a self certifying spark, notify labc before starting or do it last year.

 

[Andy Fenn]

While on the same subject, would you agree to a 32A MCB for SWA 4.0mm supply to a shed connecting to a metal 6A MCB for lights and 16A MCB for sockets.

The supply from the house c/unit will be on the RCD side.

The sockets will run mower and power tools etc but not on a heavy basis and all at the same time.

Many thanks.

 

[numpty with a crowbar]

While on the same subject, would you agree to a 32A MCB for SWA 4.0mm supply to a shed connecting to a metal 6A MCB for lights and 16A MCB for sockets.

The supply from the house c/unit will be on the RCD side.

The sockets will run mower and power tools etc but not on a heavy basis and all at the same time.

Many thanks.

I'd make it a 32A RCD at the shed end as well - that way if you get a fault from kit in the shed it'll trip the shed only, not the main RCD at the house end (thus cutting all power to all house kit on RCD). If you ain't gonna do that then you could just bin the 32A MCB as the 6A & 16 A MCBs will give you overload protection - but I'd fit an RCD as the cut-out time for the house one may be a mite too long to stop you frying in the event of a fault

 

[Spark123]

I'd make it a 32A RCD at the shed end as well - that way if you get a fault from kit in the shed it'll trip the shed only, not the main RCD at the house end (thus cutting all power to all house kit on RCD). If you ain't gonna do that then you could just bin the 32A MCB as the 6A & 16 A MCBs will give you overload protection - but I'd fit an RCD as the cut-out time for the house one may be a mite too long to stop you frying in the event of a fault

The 32A MCB at the house is still required as it provides overload and short circuit protection for the 4mm² cable.
If a 30mA RCD in the house is supplying the shed, a further 30mA RCD is not required in the shed. An RCD in the shed is very unlikely to provide discrimination if it is the same trip rating as the one in the house.

 

[ban-all-sheds]

The supply from the house c/unit will be on the RCD side.

I thought you were going to have it on the non-RCD side?

I'd make it a 32A RCD at the shed end as well - that way if you get a fault from kit in the shed it'll trip the shed only, not the main RCD at the house end (thus cutting all power to all house kit on RCD).

A 32A RCD, if such things exist, is an RCD rated to safely pass, and safely disconnect, 32A. It does not provide any overload protection, and will not trip if the current exceeds 32A.

If you ain't gonna do that then you could just bin the 32A MCB as the 6A & 16 A MCBs will give you overload protection

Yes, but they won't do anything for the cable if someone chops through it. And if he bins the 32A MCB at the house end, how is he going to connect the cable? Direct to the incomer, or the meter tails so that he'll have 4mm² cable protected by the service fuse?

but I'd fit an RCD as the cut-out time for the house one may be a mite too long to stop you frying in the event of a fault

Why should it be?

 

[numpty with a crowbar]

A 32A RCD, if such things exist, is an RCD rated to safely pass, and safely disconnect, 32A. It does not provide any overload protection, and will not trip if the current exceeds 32A.

I agree, which is why he'd need the MCB's for the overload protection, and the RDC for the disconnection

If you ain't gonna do that then you could just bin the 32A MCB as the 6A & 16 A MCBs will give you overload protection

Yes, but they won't do anything for the cable if someone chops through it. And if he bins the 32A MCB at the house end, how is he going to connect the cable? Direct to the incomer, or the meter tails so that he'll have 4mm² cable protected by the service fuse?

Ok - I mis-read that bit - though he was talking about having a 32A MCB at the shed end, then a 16 & 6A MCB's... Must have been drinking strong coffee yesterday So I was working under the impression that he's have a 32RCD / MCB at the house end, cable, then a 32MCB, followed by a 16 & 6 at the shed - hence suggestion to drop the 32 at the shed - which leads on to the MCB / RCD issue

but I'd fit an RCD as the cut-out time for the house one may be a mite too long to stop you frying in the event of a fault

Why should it be?

Would depend on the length of the cable from his RCD at the house end wouldn't it?? Now I'm no expert (far from it) but I understood that the longer the cable, the longer the disconnection time in the event of the fault? So if you're running power from the shed off a nce long extension cable, and it gets damaged, the fault's got to register down that cable, down the cable to the shed, through the house to the RCD, and then cut the power? Unless the spark who signed off the site electrics for a gig I did last year was talking out of his backside

So - as an aside from all this - if you were to fit an RCD at the shed end as well, (and Spark123 - this is your fault for confusing me ) - and you got a fault from something at the shed end (say I managed to cut through the power cable to a sircular saw for example) - would both RCD's go? Or just the one at the shed end?? Obviously if the both would then I'm wasting my time planning to fit and RCD at the shed end as well. Or would the RCD at the shed end go but not the house one?

*To confusing for a morning*

 

[oxford_30]

Right this is what I'm going to do:-

Spur of a socket into a fused switch, then from that a lead to an MK outside junction box. From here I am going to run 2.5mm SWA cable to a consumer unit in the shed with a RCD. I will then run a light circuit from a 6amp MCB. and a socket circuit from a 16amp MCB.

I belive that this will give all of the protection required......does this sound okay?

Cheers