Shed Wiring

[Greenie9657]

Hey all.

First time poster, long time reader!!!

Ive practically done every DIY job in my house looking through this site so i thought it was time i joined as i need a little advise.

I need to put lights and sockets into my shed that ive just built. Ideally id like to wire it to a mini CB panel in the garage to my consumer unit in my house but theres is no way of getting to the Consumer unit without ripping the hall, kitchen and god knows what else to hide the cabling. What ive been advised (so i just thought id check it out on here to see what you all think) is to use the exsiting outside light to run into the shed for the lighting circuit (i planned on having 2 strip lights) and using the exsiting ring main in the house to power the sheds sockets obviously lighting and sockets going through seperate FCUs which i would mount in the shed. That way if anything went wrong in the shed the house wouldnt shut down.
Any thoughts on that or even a different way of getting around my problem of an in-accessable consumer unit? Id only ever be running a freezer constantly then various power tools when i need them,(Which isnt that often.) and maybe a lawn mower or i might just pay someone as i hate gardening.

Thanks for your time.

 

[ban-all-sheds]

How far is it to the shed?

You need to consider voltage drop and fault loop impedance.

• http://www.tlc-direct.co.uk/Book/4.3.11.htm
  
  
• http://web.archive.org/web/20080213151445/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
  
  
• And why: //www.diynot.com/wiki/electrics:mcb2[/list]
  
  Have you thought about how you will get the cables to the shed, and what type of cable to use?
  • http://www.tlc-direct.co.uk/Book/7.13.1.htm
    
    
  • //www.diynot.com/wiki/electrics:swa-gland
  
  By the sounds of it you won't have any extraneous-conductive-parts in the shed, but if you do, and if you have a TN-C-S (PME) supply then you'll need to decide what to do about exporting the earth, or not, to the shed.
  • http://electrical.theiet.org/wiring-matters/16/elect-inst-outdoors.cfm?type=pdf[/list]
    
    You'll need to test the work once it's done, before and after energising, so that you know it's safe.
    • http://www.tlc-direct.co.uk/Book/8.1.1.htm[/list]
      
      You say "That way if anything went wrong in the shed the house wouldnt shut down", but what about RCD trips?
      
      
      Given the decisions and skills involved, it might make more sense to use an electrician, who might have ideas about getting to the CU when he sees the job.
      
      On a non-electrical note, you need to be careful about putting freezers in outbuildings - most won't work properly if they are somewhere cold.

 

[Greenie9657]

How far is it to the shed?

You need to consider voltage drop and fault loop impedance.

• http://www.tlc-direct.co.uk/Book/4.3.11.htm
  
  
• http://web.archive.org/web/20080213151445/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
  
  
• And why: //www.diynot.com/wiki/electrics:mcb2[/list]
  
  Have you thought about how you will get the cables to the shed, and what type of cable to use?
  • http://www.tlc-direct.co.uk/Book/7.13.1.htm
    
    
  • //www.diynot.com/wiki/electrics:swa-gland
  
  By the sounds of it you won't have any extraneous-conductive-parts in the shed, but if you do, and if you have a TN-C-S (PME) supply then you'll need to decide what to do about exporting the earth, or not, to the shed.
  • http://electrical.theiet.org/wiring-matters/16/elect-inst-outdoors.cfm?type=pdf[/list]
    
    You'll need to test the work once it's done, before and after energising, so that you know it's safe.
    • http://www.tlc-direct.co.uk/Book/8.1.1.htm[/list]
      
      You say "That way if anything went wrong in the shed the house wouldnt shut down", but what about RCD trips?
      
      
      Given the decisions and skills involved, it might make more sense to use an electrician, who might have ideas about getting to the CU when he sees the job.
      
      On a non-electrical note, you need to be careful about putting freezers in outbuildings - most won't work properly if they are somewhere cold.

• • • 
      
      Thanks for your post, the gap for the sockets will be about 1 metre and for the lights even less.

 

[Greenie9657]

Sorry Shed, i didnt see the rest of your questions.

Ill be going into it the roof so i wont need armoured cabling. What i ment witht the RCDs is that ill fit those to each of the circuits in the shed that way if i trip anything in the shed then at least i wont get abuse from the wife for blowing the house CD.
The shed is concrete block built not the wooden variety.
The main consumer unit is under the stairs right at the front of the house and the shed is out the back so unless a sparky could invent wireless mains voltage (in which case he would be minted!!), i cant see anyway of connecting the CU to the garage. Im going to get a qualified sparky in to fit a new box and maybe re-position it as its old anyway.

Thanks again

 

[ban-all-sheds]

Thanks for your post, the gap for the sockets will be about 1 metre and for the lights even less.

So the shed is less than 1m from the house?

Ill be going into it the roof so i wont need armoured cabling.

So overhead?

You'll still need to use cables suitable for external exposure (not twin & earth), and supported, but over that sort of distance it's not major engineering.

What i ment witht the RCDs is that ill fit those to each of the circuits in the shed that way if i trip anything in the shed then at least i wont get abuse from the wife for blowing the house CD.

No guarantee of any of that - an RCD in the shed won't necessarily trip before the one in the house.

The main consumer unit is under the stairs right at the front of the house and the shed is out the back so unless a sparky could invent wireless mains voltage (in which case he would be minted!!), i cant see anyway of connecting the CU to the garage. Im going to get a qualified sparky in to fit a new box and maybe re-position it as its old anyway.

Talk to him about it.

Would you mind a cable clipped to the outside of the house?

Do you have an external meter box with a bit of space in it?

 

[Greenie9657]

no external box shed, everything is in the house and all in the same place, under the stairs at the front. The shed has been built to kind of seal the back garden in via a gate so thats why its pretty close to the house. To be honest im not too worryied out the lighting side i need advise really for the sockets.

Thanks again for your help

 

[ericmark]

It worries me to offer advice on shed wiring as it is so easy to miss something which in turn could change the whole system. However you say your getting an electrician so I am going to give the idea of what can be done knowing if there is something missed he will pick up on it.

1) Supply from house it would seem a FCU with 13A fuse is ample. What you need is a method of physical connection often using a surface metal box will allow the use of SWA or good stuffing glands. Using a surface metal box outside with a lid and no connections in the box is another way of physically attaching the cable.

2) With the exception of caravan and boat supplies the putting of two RCD's in tandem with same tripping values is pointless. Although 10ma RCD's are made they are hard to locate and expensive plus although the tripping current is reduced the tripping time is not so any real fault is still likely to take out both RCD's. In some cases due to distance or external metal parts to the outbuilding TT supplies are used in this case the a second RCD would be required but from what you say unlikely in this case.

So the likely method would be two FCU's one supplying shed from house and a switched version in shed to control lights with a 3A fuse fitted.

If there is no RCD protection in the house then a RCD FCU for supply to shed would be way to go. There are two types of RCD FCU passive and active and the selection is dependent on the loop impedance where the device is fitted. With a good loop impedance a passive type can be used which means after a power cut the shed will still have power. Where the loop impedance is too high an active type is used. This means under fault conditions should the voltage drop below the operating voltage for the RCD it will trip anyway i.e. fail safe.

Your electrician will tell you which you can use. If not sure then select an active type.

I would get the electrician first before buying any parts. I have arrived to do work where the home owner has bought all the parts only to find because the supply is TT rather than TN-C-S or reverse the items are not suitable.

The main point for simple shed wiring I see no point in either twin supplies (sockets and lighting) or consumer units in the shed. Using a switched FCU for the light switch makes it all so much easier.

 

[JohnW2]

There are two types of RCD FCU passive and active and the selection is dependent on the loop impedance where the device is fitted. With a good loop impedance a passive type can be used which means after a power cut the shed will still have power. Where the loop impedance is too high an active type is used.

Eric, could you possibly explain to me the thinking behind that statement? It sounds almost as if you are saying that it's OK if the EFLI is too high for an RCD to operate (i.e. extremely high), but if that's the case one uses an active RCD just for its 'no-volts-disconnect' functionality. Thanks.

Kind Regards, John

 

[RF Lighting]

I was taught to use active RCDs where unexpected starting could pose a hazard such as heaters or power tools, and passive for everything else such as lighting, freezers etc.

AFAIK, there is no other factor to influence selection, and EFLI must be low enough to cause the device to operate regardless of which type it is.

 

[JohnW2]

I was taught to use active RCDs where unexpected starting could pose a hazard such as heaters or power tools, and passive for everything else such as lighting, freezers etc. AFAIK, there is no other factor to influence selection, and EFLI must be low enough to cause the device to operate regardless of which type it is.

Thanks. That's exactly my understanding, too - which is why I was more than a little surprised/confused by what Eric wrote.

Kind Regards, John

 

[Greenie9657]

Thanks again for all your help. I've just been shown a neighbours garage who did what I'm trying to do and this is the set up.

Ring main cable spured from upstairs into the garage
Connected to a FCU of 10A in the garage. 1 cable going into FCU.
Coming out of the FCU is 2 Cables
One goes around the garage to have 3 double sockets on it.
The other goes into another FCU which has a 3A fuse in it.
That then supplies the lighting.

Thinking about this it would work but is it legal and can it be done with all the part P and regs involved? It would make a lot let mess as I'd only have the one spur going in, instead of the ring and the lighting.

Once again with these 1930s house, the consumer unit is totally inaccessible to the garage. Otherwise it would make it a lot easier, but like I said that is not an option at the minute.

 

[Greenie9657]

Well just to keep you updated I've wired it all up like the last post I did and it all works spiffingly. My only problem is where the hell to connect it in the house.
I wanted to spur it into the upstairs ring as that has less loads on it than the down stairs main but I can't get it in the house upstairs for anything.
No where through the roof inside or out. It's proper sealed. Would there be any problem in wiring it to the downstairs main? That would be so much easier too.
I was just worried about the loads being used at the same time. Just to test the electrics in the shed I wired the supply up with a plug to make sure everything worked.
Any help would be great?

 

[ban-all-sheds]

Ring main cable spured from upstairs into the garage
Connected to a FCU of 10A in the garage.

That FCU should be at the origin of the spur, not at the end of it. And it might as well be 13A.

Thinking about this it would work but is it legal

Arguably not - the cable to the garage is almost certainly too long to be on a 32A breaker.

Well just to keep you updated I've wired it all up like the last post I did

Oh dear.

What type and size cable did you use?

And if it comes from the ground floor, what route will the cable take to get into the shed?

Just to test the electrics in the shed I wired the supply up with a plug to make sure everything worked.

http://www.tlc-direct.co.uk/Book/8.1.1.htm

 

[Greenie9657]

Hi shed. Just for the test I used 2.5mm and it was through to top corner of the shed from a little higher on the house.

 

[ricicle]

There are two types of RCD FCU passive and active and the selection is dependent on the loop impedance where the device is fitted. With a good loop impedance a passive type can be used which means after a power cut the shed will still have power. Where the loop impedance is too high an active type is used. This means under fault conditions should the voltage drop below the operating voltage for the RCD it will trip anyway i.e. fail safe.

Absolute rubbish.