Electrics in a shed...

[Mtree]

I have an old wooden shed that I wired up with lights and sockets around about 7 years ago. Although I've had no problems I know what I did wasn't right.

Basically, I ran a length of flex from my shed to the kitchen. Where the flex entered the kitchen through the wall I screwed a junction box over it and continued on with a piece of cable with a plug on the end. This allowed me to disconnect the power to the shed whenever I wished.

After the flex entered the shed I brought this into a junction box and split off with one piece of flex creating my plug socket ring and the other my lights.
Each circuit also had its own switch to isolate the circuits.

So right off the bat I know that the cable in the kitchen wasn't thick enough. I also know that the plugs and lights shouldn't have run off the same household plug circuit but I figured it would be ok and it has.

Now I'm building a new brick shed and outbuilding. I need power and lights again but want to be safe. What should I do different.?

 

[Greenie9657]

Hi mate

How far is the shed away from the house? (Consumer unit)

 

[sparkwright]

The best way is to run an armoured cable from the house consumer unit to the shed. Here either a small consumer unit is fitted. Alternatively the lights are fed by a fused spur unit.

But we need to take into account cable run length between house and shed, assumed maximum current demand, earthing arrangement, cable sizes, RCD protection.

More info required. Good electrical experience is needed to carry out this work properly, so getting a pro to do most of the work is the best option.

 

[doingitmeself]

Now I'm building a new brick shed and outbuilding. I need power and lights again but want to be safe. What should I do different.?

Call a professional electrician and have them quote you for doing the job properly.

 

[JohnW2]

The best way is to run an armoured cable from the house consumer unit to the shed. Here either a small consumer unit is fitted. Alternatively the lights are fed by a fused spur unit. ... But we need to take into account cable run length between house and shed, assumed maximum current demand, earthing arrangement, cable sizes, RCD protection. ... More info required. Good electrical experience is needed to carry out this work properly, so getting a pro to do most of the work is the best option.

Not only that but, if it is done as you suggest, it would be notifiable work ('new circuit'), and therefore quite possily cheaper to get a pro to do it.

Kind Regards, John

 

[Mtree]

Hi mate

How far is the shed away from the house? (Consumer unit)

about 6 meters

 

[ban-all-sheds]

Call a professional electrician and have them quote you for doing the job properly.

 

[Greenie9657]

If i was doing it id use 6mm2 SWA from the CU in the house to a mini CU in the garage. Some people say there isnt any point RCD protection in the house and in the garage but its up to you. I will be.(you can buy dedicated garage CUs from most diy shops). Depending what you use the garage sockets for, if its heavy power tools then some will argue that 10mm2 SWA would be needed.
Ive got a mate who has done it all with 2.5mm SWA and although i wouldnt go that small he hasnt had any problems with it and he did that well over 5 years ago. Just make sure you earth it all properly.

 

[Mtree]

If i was doing it id use 6mm2 SWA from the CU in the house to a mini CU in the garage. Some people say there isnt any point RCD protection in the house and in the garage but its up to you. I will be.(you can buy dedicated garage CUs from most diy shops). Depending what you use the garage sockets for, if its heavy power tools then some will argue that 10mm2 SWA would be needed.
Ive got a mate who has done it all with 2.5mm SWA and although i wouldnt go that small he hasnt had any problems with it and he did that well over 5 years ago. Just make sure you earth it all properly.

What's SWA?

I agree with what you are saying though. I was thinking of running a power and lighting cable from the CU through the loft and across the garden above head height to the shed.

I've been reading online that you can lay the cables on top of the insulation. This seems a little dangerous to me, would it be ok to run them inside some kind of protective sleeve together until they reach the shed?

 

[RF Lighting]

Call a professional electrician and have them quote you for doing the job properly.

 

[riveralt]

What's SWA?

Which perhaps suggests that you aren't really up to the job and should, as others have said, get an electrician in to assist.

I agree with what you are saying though. I was thinking of running a power and lighting cable from the CU through the loft and across the garden above head height to the shed.

SWA - when you learn what is it - is heavy and you will need some strong support, since without it the strain on your termination points may be dangerous.

I've been reading online that you can lay the cables on top of the insulation. This seems a little dangerous to me,

Why would you consider it dangerous?

would it be ok to run them inside some kind of protective sleeve together until they reach the shed?

Sure as long as you take into account any de-rating factors.

 

[Mtree]

What's SWA?

Which perhaps suggests that you aren't really up to the job and should, as others have said, get an electrician in to assist.

I agree with what you are saying though. I was thinking of running a power and lighting cable from the CU through the loft and across the garden above head height to the shed.

SWA - when you learn what is it - is heavy and you will need some strong support, since without it the strain on your termination points may be dangerous.

I've been reading online that you can lay the cables on top of the insulation. This seems a little dangerous to me,

Why would you consider it dangerous?

would it be ok to run them inside some kind of protective sleeve together until they reach the shed?

Sure as long as you take into account any de-rating factors.

I came here because i want to save some money. If I wanted an electrician I would call one. I want to do this myself. I do all my own stuff. I'm willing to learn.

Laying cables on top of the insulation seems dangerous to me because when people go up there (and they do - my virgin media cables are up there, I use the loft for storage etc..) it would be easy for someone to pull the cable with their foot. Its a small loft that requires crawling to get past the water tanks...

A plumber already pulled out my intercom cable without noticing.

Please explain de-rating factors.

 

[EFLImpudence]

Someone will later post links to useful publications which because of your admirable desire to learn you will appreciate.

 

[riveralt]

Okay, fair enough, if you want to do the work you have outlined (new circuit from the CU to your new outbuilding) yourself then the first thing you will need to do is to apply to your Local Authority Building Control and pay their fee £201.60. This must be done before work has commenced.

All electrical work you do will have to comply with the current building regulations and in particular Part P of the Approved Documents - you may also have to make reference to other Approved documents dependent on where your cable run goes.

You will need to have access to properly calibrated test gear able to determine Continuity, Insulation Resistance @ 500v dc, External Loop Impedance, Prospective Fault Current and have the ability to test RCD's.

You should also be able to complete an Electrical Installation Certificate etc and be able to use the test gear to determine that the results you get for the above tests are within the limits laid down by BS7671.

You will have to design your new circuit - taking into account your current earthing arrangement - is it TT TNS TNCS? You need to ensure that your current earth arrangements, in particular the cable size is within the guidance outline in BS7671.

You will need to determine that the External Loop Impedance Ze is within guidelines since that will have an impact on the Earth Loop Impedance which is determined by Ze +R1+R2.

The size and type of cable you use is determined by a number of factors including the load, the type of circuit you intend to create the circuit length (don't forget Voltage drop calculations - since this will affect the size of the cable). Dependant on the above you may have to introduce an RCD into the circuit - does your CU current have RCD or RCBO protection?

If not, don't worry, because you can probably split the meter tails by putting them into a Henley Block and running new tails to your old CU and a new small CU containing an RCBO or similar protection. Just make sure you have an isolator fitted before this work is carried out otherwise you will have to call out your DNO to pull the main fuse why you carry out this work.

Your new cables should be run in safe zones and comply with H&S in terms of trips and hazards etc - if the plumber didn't know that he had pulled the intercom cable out then perhaps there is an issue re trips and hazards.

etc etc etc.
So I think the starter for ten is to inform your LABC and listen to their advice - what do you think?

 

[ban-all-sheds]

I want to do this myself. I do all my own stuff. I'm willing to learn.

• 
  
  
  
• //www.diynot.com/wiki/electrics:books
  
  
• //www.diynot.com/wiki/electrics:mcbtocable
  
  
• http://www.tlc-direct.co.uk/Book/4.3.1.htm (all subsections)
  
  
• http://www.tlc-direct.co.uk/Book/4.3.11.htm
  
  
• http://web.archive.org/web/20070327014113/http://www.kevinboone.com/cableselection_web.pdf
  
  
• http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html
  
  
• http://www.tlc-direct.co.uk/Book/5.3.1.htm
  
  
• //www.diynot.com/wiki/electrics:mcb2
  
  
• http://www.tlc-direct.co.uk/Book/7.13.3.htm
  
  
• http://www.tlc-direct.co.uk/Book/8.1.1.htm
  
  
• //www.diynot.com/wiki/electrics:swa-gland
  
  
• http://electrical.theiet.org/wiring-matters/16/elect-inst-outdoors.cfm?type=pdf
  
  
• //www.diynot.com/wiki/electrics:part-p
  

Please explain de-rating factors.

You'll find that as you go through the 3rd link in the list above.

Sadly that on-line electricians guide refers to the previous edition of the Wiring Regulations, but it will still stand you in good stead - the latest publications are referenced in the first link.