Advice on running electrics to shed

[Hypnotic Chimera]

Hello all

Looking for anyone knowledgeable enough to tell me whether I need a qualified electrician to do a job for me or whether I can legally perform the job myself.

I have electrics in my garage. Dedicated spur and fed from house CU. There's clearly a SWA connection and it runs underground, certified from when the house was built 17 years ago - I would assume this wire is sunk at the appropriate depth, etc.

The CU in the garage has 2 circuit breakers - one for lighting and one for sockets.

The garage is about 12 metres from the shed project (another thread).

Is it possible to DIY a connection from the garage CU or from the garage electrics themselves? Wires ideally located on a wooden feather-board boundary fence or the retaining wall that the fence situated above.

All I'm after in the shed is a light or two and a socket or twin for "small" duties. No power tools - just maybe a battery charger/phone charger or radio/Alexa+speaker?

For temporary lighting setup I've been using a 300W halogen bulb wander lamp, connected via a socket extension, but extension only unreeled and plugged in when I've been working inside the shed.

Thanks in advance.

 

[Spectric]

I would think the electric's in your garage are probably the bare bones for a light and socket as fitted during the build of the property. You are looking to extend this supply to another outbuilding for a light and a socket but you have not mentioned the means of earthing in the actual property or given enough details. You cannot just run any cable along a fence unless it is mechanically protected and it would require a protective device such as an RCBO in the garage. I doubt you have the test equipment required to ensure loop impedances are suitable for cable lengths or disconnection times for protective devices comply with the regs so for your own safety it would be better to just get an electrician to undertake the job if you want a permeant supply otherwise you will need to use temporary extensions when required.

 

[Hypnotic Chimera]

I would think the electric's in your garage are probably the bare bones for a light and socket as fitted during the build of the property. You are looking to extend this supply to another outbuilding for a light and a socket but you have not mentioned the means of earthing in the actual property or given enough details. You cannot just run any cable along a fence unless it is mechanically protected and it would require a protective device such as an RCBO in the garage. I doubt you have the test equipment required to ensure loop impedances are suitable for cable lengths or disconnection times for protective devices comply with the regs so for your own safety it would be better to just get an electrician to undertake the job if you want a permeant supply otherwise you will need to use temporary extensions when required.

Thanks Spectric - appreciate the swift reply.

Garage has B16 socket and B6 lighting protection. Lighting is 2 x 4ft strips and a 300W security light on a PIR. Sockets are 2 x twins, but I only use 1 socket at the back for a fridge freezer and the twin at the front are mainly for my DIY tools or power washer on an extension reel to the driveway.

I understood about protecting the wire and RCBO from reading up on what is notifiable or not, but as you say I don't have professional test equipment. I wondered whether using SWA would imply a requirement for a separate CU in the shed, or whether just a simple T&E inside a conduit was acceptable. Can't find much on that - maybe because it is a touchy area.

Sems like a visit from a spark is the way to go.

 

[ChaiLatte]

Make your temporary extension lead a little more permanent in location but without making it part of the fixed installation.

Buy a 15m extension lead with a four gang outlet and remove the plug (https://www.industrialextensionlead...y-13amp-25mm-cable-extension-lead-11189-p.asp). Poke the cable through some 20mm plastic conduit clipped to the fence. Install new plug on end of lead and plug into existing socket in garage.

Providing you do as you say and do not exceed the capacity of the extension lead, it is the same as your existing arrangement only you do not coil it back up after use.

As it is not part of a fixed installation you do not need any special qualification for the work. The moment in time and point in space when and where you involve yourself in the fixed wiring is where the regulations kick in.

The only competence you need to route the extension lead is in removing and fitting a standard plug. Because it is plugged into an existing socket, it will inherit all the protection of the circuit on which that socket is fitted.

 

[Hypnotic Chimera]

Make your temporary extension lead a little more permanent in location but without making it part of the fixed installation.

Buy a 15m extension lead with a four gang outlet and remove the plug (https://www.industrialextensionlead...y-13amp-25mm-cable-extension-lead-11189-p.asp). Poke the cable through some 20mm plastic conduit clipped to the fence. Install new plug on end of lead and plug into existing socket in garage.

Providing you do as you say and do not exceed the capacity of the extension lead, it is the same as your existing arrangement only you do not coil it back up after use.

As it is not part of a fixed installation you do not need any special qualification for the work. The moment in time and point in space when and where you involve yourself in the fixed wiring is where the regulations kick in.

The only competence you need to route the extension lead is in removing and fitting a standard plug. Because it is plugged into an existing socket, it will inherit all the protection of the circuit on which that socket is fitted.

This sounds like an eminently sensible way forward, at least in the short term. Lighting would be modern low power (outside IP66) LED anyway and could be on a plug with an inline switch - I would imagine acceptable due to low power draw and temporary plug/socket setup.

 

[Fitzroy]

Ran my shed from an extension cable for nearly 4 years. Had proper electrics installed earlier this year, so much nicer to have a light switch and some sockets in sensible places. Use an extension to get by for now but plan to get the electrics done sooner rather than later.

 

[Sideways]

Because it is plugged into an existing socket, it will inherit all the protection of the circuit on which that socket is fitted.

This is the key.
As I see it, you could make that extension cable a length of steel wire armor, terminate it indoors at each end in metal clad boxes from Screwfix / Toolstation and feed it from a short length of 1.5mm flex fitted with a 13A plug.

This isn't fundamentally any different from @ChaiLatte 's suggestion just well protected from the elements and accidental damage.
Something downstream of a 13A plug isn't part of the fixed wiring as I see it. If I'm seeing it wrongly, I'd be interested to understand why.

 

[ChaiLatte]

..you could make that extension cable a length of steel wire armor...

If there was a place on the fence at each end to make a neat couple of extra loops of the SWA cable, it could allow that same cable to be used in the future if the arrangement was ever made permanent by an electrician. Would save buying a whole new cable.

If you look on the railways they do this a a lot with their cables: reach the nominal end point of the run and then make a big coil of it clipped onto trays. I guess it gives them future options without re-running the whole length.

 

[Dabop]

In Australia- any wiring that is 'permanently fixed' is classified as 'permanent' (regardless of its wiring type originally) so an extension cord that is run in conduit- or even just nailed to the wall with clips is indeed classified as 'permanent' here and as our regs are heavily based on BS standards, I would look into if the UK's standards are similar... (regardless of what you 'feel' it should be, it is what is written into the regs that count...)


Also, using SWA is something that I have seen done incorrectly far too many times in the past to be comfortable with just anyone doing it themselves... (ungrounded armor, inner cords nicked while cutting the armor, top feeds on exterior boxes, rubber boots cut oversized allowing water entry- seen all these- multiple times myself...) and as Spectric mentioned- is adding the extra length going to take you out of the safe loop impedance range (once your lengths get long enough the current carrying limit becomes almost completely ignorable- voltage drop (operational AND in short circuit conditions) becomes a major factor- with light cables AND long lengths, you can hit the situation where even a direct short circuit at the far end will never actually trip the breaker/blow the fuse!!! (the added resistance in the cable because of the length means it is dissipated as heat in the cable and the current never rises above the limit of the breaker!!!- worse it can render many earth leakage breakers either insensitive, or some types even totally inoperative at the far end!!)

Another factor is that while 'you' may know its a limited supply- will anyone and everyone else know it also??? (especially if it is fitted with a standard GPO/outlet at the far end)- 'you' (heaven forbid) pass away suddenly, and the next person comes along and plugs in a heavy duty tool that would tax even a 'proper' installation- and the only protection is the original fuse/MCB, but the added length (and remembering that normal' extension cords usually have a much smaller wiring size internally than 'proper' fixed wiring) you could end up with excessive voltage drop and overheating issues in those lengths of cables... (especially as they age)

To show what I mean, these are a 'extra heavy duty' 15A caravan/heavy power tool extension cord, and the fixed TPE used for a standard 10A outlet from one of our local hardware stores...

Note the size difference in the conductors- 1.5mm^2 for the 15A 'extra heavy duty' and 2.5mm^2 for the fixed wiring (nearly twice the size!!!) and the UK uses ring circuits so you have effectively got a paralleled pair of 2.5's feeding a non spurred outlet... a single one for a fused spur off the ring...

And I have personally seen a 'light duty' extension cord being used in a 'shed feed'- they only have 1mm^2 cables!!!- originally installed 'just to run a light and radio in the shed'- and ended up having power tools, a fridge and a heater all running at the same time off it!!!! (the end had been cut off and a standard powerpoint fitted to it 'for convenience' a bit later on, then a power board plugged into that later on again, then the fridge added 'to keep my beers cold in summer', then the heater because 'winters are cold down south and I'm feeling the cold at my age'- and then 'everything stopped working- could you have a look at it mate???'

He had literally forgotten about that extension cord (installed back in the 70's!!!) that was feeding everything...

It had performed mightily over the decades- but that heater was the final straw and the wires inside had literally melted off the crimped connections in the factory plug!!!! (and the cables weren't much better, with heavily overheated insulation evident everywhere I cut into it...)
😱

 

[Hypnotic Chimera]

This is the key.
As I see it, you could make that extension cable a length of steel wire armor, terminate it indoors at each end in metal clad boxes from Screwfix / Toolstation and feed it from a short length of 1.5mm flex fitted with a 13A plug.

This isn't fundamentally any different from @ChaiLatte 's suggestion just well protected from the elements and accidental damage.
Something downstream of a 13A plug isn't part of the fixed wiring as I see it. If I'm seeing it wrongly, I'd be interested to understand why.

Funny you mention SWA - I have some in my Amazon basket already. The junction boxes sound like another appropriate addition.

 

[Hypnotic Chimera]

It had performed mightily over the decades- but that heater was the final straw and the wires inside had literally melted off the crimped connections in the factory plug!!!! (and the cables weren't much better, with heavily overheated insulation evident everywhere I cut into it...)

A lot of great stuff there, thanks mate.

 

[Dabop]

Funny you mention SWA - I have some in my Amazon basket already. The junction boxes sound like another appropriate addition.

Did you check to see if it would be usable for a 'proper' installation later???
(because it is a 'spur off a spur' and relatively long distance at that, you might have to go up a size from 'normal' to keep loop impedance within safe limits at the far end (ie you 'may' depending on the already existing feed to the tap point, have to go up to a say 4mm^2 instead of a 2.5mm^2 depending on the TOTAL length of the run (thats the original feed your are using AND the length of the new run added together)

Otherwise an electrician later may have to rip it all out and start again from scratch!!!!

(it isn't the current carrying capability that is important on these long runs, but the loop impedance (conductor size) that counts...)

Many think that just having the conductor size rated for the current limit means it is 'OK'- nope... Another run I did had to use 35mm^2 cable (current limit over 135A!!!!) just to supply a tiny15A feed to a remote shed on a farm!!!! it was a 300m run- and that 35mm^2 was just barely at the the MINIMUM required for a 15A feed !!!
😱

 

[Hypnotic Chimera]

Did you check to see if it would be usable for a 'proper' installation later???
(because it is a 'spur off a spur' and relatively long distance at that, you might have to go up a size from 'normal' to keep loop impedance within safe limits at the far end (ie you 'may' depending on the already existing feed to the tap point, have to go up to a say 4mm^2 instead of a 2.5mm^2 depending on the TOTAL length of the run (thats the original feed your are using AND the length of the new run added together)

Otherwise an electrician later may have to rip it all out and start again from scratch!!!!

(it isn't the current carrying capability that is important on these long runs, but the loop impedance (conductor size) that counts...)

Many think that just having the conductor size rated for the current limit means it is 'OK'- nope... Another run I did had to use 35mm^2 cable (current limit over 135A!!!!) just to supply a tiny15A feed to a remote shed on a farm!!!! it was a 300m run- and that 35mm^2 was just barely at the the MINIMUM required for a 15A feed !!!
😱

Yep - understood, thanks (I did some electrical engineering academics during my aeronautical engineering degree).

I think since this is such a "controlled" topic there is precious little that I can find on the internet - which I entirely understand for the reasons that are evident in this thread.

 

[Dabop]

As you might have gathered, I do have a little experience in the field ;-)
And because it is something outside many peoples experience, they apply 'what normally works' not thinking that there are factors that make that experience useless- or even dangerous...

That last 300m shed run for example- I have had some (who aren't even trained in the field) say 'you should always size the breaker/fuse to the current carrying capability of the cable- which is incorrect in these longer runs (well any run really, but it is obviously magnified on a really long run) That shed run had a 15A breaker at the 'house' end, and a 10A breaker on the shed end- to feed a single powerpoint and a single light!!!- all hanging off a cable rated at 135A!!!

It needed to be that size simply to be able to trigger the 15A breaker at the house end if a short happened in the cable at the shed end (thats that 'loop impedance' Spectric and I were talking about earlier- a smaller cable simply has too much resistance in the copper to actually exceed the current limit of the breaker, even into a direct short circuit!!!- you effectively make a 300m long 'electric heater' that never rises above the current limit on the breaker at the feed end!!!

Yours isn't quite that extreme obviously, but any time you are adding extra length (especially to a 'spur off a spur'- which was already likely right at the lower limits of acceptable to begin with (because its cheaper to just barely meet the specs than massively oversize them) that new spurs limits have to be very carefully calculated...
What happens later if someone plugs a long extension cord into that new extension spur outlet for example- now you have a REALLY long length to account for in your safety factors....

It's why so many places have either discouraged DIY electrics, or made them totally illegal at all....
Some of the things I have seen myself-urghhhh......

 

[Hypnotic Chimera]

I get it, entirely, and will probably avail myself of an electrician in the next week or 2.

I'm reading your stuff about "barely acceptable" new build electrics and wondering to myself now whether what I currently (pun intended) do with it is "safe"?

I run a reeled 2-socket 25 metre extension from a garage socket.
Into that reeled extension - partially unreeled - I plug a 1000W(?) dust vacuum (Evolution R15-VAC) with an 1500W mitre saw in the dust vacuum pass-through power socket.

This use case, I would have assumed, "should" have been catered for in the design and realisation of the garage electrics...

 

[Spectric]

any wiring that is 'permanently fixed' is classified as 'permanent' (regardless of its wiring type originally) so an extension cord that is run in conduit- or even just nailed to the wall with clips is indeed classified as 'permanent' here and as our regs are heavily based on BS standards, I would look into if the UK's standards are similar.

That is one of those grey areas open to debate, in general if you fix an extension lead to then power say some fridges in your cafe and it is clipped round say a door frame it is technically classed as fixed not because it is clipped but because the fridges are not a temporary load. Extension leads are used to supply things where there is no power that is required short term such as a lawnmower, a power tool to sand something in a garden etc etc. There are similar issues with PAT testing that applies to portable equipment, define portable ? A hand dryer in a toilet fixed to the wall but with a flexable lead from a fused outlet is classed as portable and the same for a large welding set that might need a crane to move it is also portable even if you cannot move it without other machinery. Here the supply cable is the giveaway, anything even if fixed down but powered by a flexable supply cable is "Portable" because one of the objectives of PAT testing is to ensure that the protective conductor is capable of handling a current and not just continous. Here a flexable cable is more liable to damage such as almost but not quite broken CPC .

If running an extension to your other shed how ever done then ensure you have an RCD plugged into the outlet socket.

 

[Sideways]

I disagree somewhat with the above.
There has been some rumour and confusion over it since about the 15th ed of the UK wiring regs but it is perfectly clear that flexible cable can, even should, be used in appropriate situations as part of the fixed wiring.
Flex doesn't mean something is not part of the fixed installation.

Discussed here at the IET.
https://electrical.theiet.org/wirin...les-are-not-permitted-in-fixed-installations/

However, the moment you unplug something - an appliance, an extension lead - it's not part of the fixed wiring. I can't think of any paragraph in the wiring regs that says something which can simply be unplugged was ever part of the fixed installation. If anyone does have a reference in BS7671 do please share it.