WIRING A SHED

[STUART SIMPSON]

I have bough a new shed and want to use it as a workshop. I have bought a garage/ shed consumer unit rated at 63A 30mA RCCB with 1x 6A and 1 x 16A MCBs.

I want to take the power for this from an old shower circuit which has been switched off. The shower was on its own single fuse box (30 amp) wired into the busbar on the consumer unit. And the 6mm cable still goes into the loft albeit it is dead because the fuse box is switched off and fuse removed.

My plan is to make a junction box up in the loft and join outdoor cable to the existing 6mm cable that powered the shower and lead this outside overhead to the consumer unit in the shed. Is it ok to join a smaller cable (2.5mm) to the 6mm cable because i cant renew the cable all the way back to the old fuse box that powered the shower.

Also the fuse box for the shower is rated at 45amp but has a 30 amp fuse in it, do i need to downgrade this as i don't think i will need 30 amps of power going to the shed. Or would i be better just taking the old shower fuse box away and wiring direct to the busbar?

Cheers for the help

Stuart

 

[ban-all-sheds]

Please just get an electrician.

1. It is clear from the questions you are asking that you do not have anywhere near enough understanding to be doing this work.
   
2. I'll bet what's left of my pension that you don't even know about testing, let alone have the equipment to do it.
   
3. You need Building Regulations approval for this, and they won't let you DIY because of 1 & 2.
   

 

[JohnW2]

Stuart, I know it won't be what you want to hear, but what you write raises so many potential issues that I really think you would be best advised to employ the services of an electrician.

Kind Regards, John

 

[STUART SIMPSON]

Hi John

Thanks for your reply mate. what issues are there if you wouldn't mind explaining a bit more. Am not a numpty but a don't know all the regs, just a bit of advice on how you would do it would be great.

Cheers mate

 

[ban-all-sheds]

• 
  
  
  
• [wiki]Electrics%3Abooks[/wiki]
  
  
• [wiki]Electrics%3AMCBtoCable[/wiki]
  
  
• 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 <- Specify 2-core cable and PVC, even if that is not what you are using or it will make invalid assumptions.
  
  
• http://www.tlc-direct.co.uk/Book/5.3.1.htm
  
  
• [wiki]Electrics%3AMCB2[/wiki]
  
  
• http://www.tlc-direct.co.uk/Book/7.13.3.htm
  
  
• http://www.tlc-direct.co.uk/Book/8.1.1.htm
  
  
• [wiki]Electrics%3ASWA_gland[/wiki]
  
  
• http://electrical.theiet.org/wiring-matters/16/elect-inst-outdoors.cfm?type=pdf
  
  
• [wiki]Electrics%3APart-P[/wiki]
  
  The references above which are in italics are out of date. The principles are still valid, and you can absolutely learn valid things from them, but you will need to refer to the latest edition of the Wiring Regulations to get the correct data.

 

[flyingsparks]

Sometimes I think BAS is a bit OTT when telling people to get an electrician, however in this particular case I totally agree with him! (And John)..

 

[STUART SIMPSON]

Cheers for the reply, how would you wire it mate?

 

[Taylortwocities]

Cheers for the reply, how would you wire it mate?

He would wire it properly, that means in accordance with the Wiring Regulations. BAS's link is out of date! This is the version that you would need.

 

[STUART SIMPSON]

But how would you wire it mate. Am competent at doing it a just want to know what is the best way. Is the 6mm cable to heavy for example?

 

[flameport]

Or would i be better just taking the old shower fuse box away and wiring direct to the busbar?

Doing that is dangerous and could end with your house on fire.

The rest of your plan is mostly incorrect as well.

You cannot do this work yourself.

 

[Taylortwocities]

Am competent at doing it a just want to know what is the best way.

You cannot be competent, as you are asking simple, elementary questions - that's why you aren't getting any help.

For example, you asked

Is the 6mm cable to heavy for example?

How can a cable be too heavy ? (unless you mean physical weight). The design issue with cable is that it is too small for the design current.

 

[ban-all-sheds]

BAS's link is out of date!

Oh poo. Thanks. I'll change it. Better do the Wiki too. I wish they wouldn't bring new versions out so often.

This is the version that you would need.

Cheaper here: https://www.tlc-direct.co.uk/Main_Index/Books_Training_Index/Electricians_Guide_Book/index.html

 

[STUART SIMPSON]

Cheers for the reply but can you tell whats wrong with the plan. I didnt think i should wire it direct to the busbar. I though it shoukd be on a fuse, what size? Is the 6mm cable to heavy going into the loft or should i continue 6mm outside to the shed aswell? Its a shed for using a few power tools and a light.

 

[AndyPRK]

Normally you would wire it with swa cable in the ground
Buried at the correct depth and marked correctly.

Typical fuse would be 16 or 20 a depending on cable used.

 

[ban-all-sheds]

But how would you wire it mate.

With the correct cable type(s), installed in the correct way, and the correct cable sizes to maintain Ib ≤ In ≤ Iz when all the derating factors and voltage drop are taken into account.

But then you already knew that, as you are competent.

Care to tell us what tests you would carry out on the installation - what sequence you'd do them in and at what point you would energise the installation, and for each test what is being measured, why it is important, how you would carry out the test, and with what equipment, and what sort of results you would expect to get if everything was OK?

The thing is this is a far more complex job than you think it is and I can assure you that it involves knowing far more than you think it does.

Asking questions here can be a useful part of a learning process, but they are not a substitute for proper structured studying. The key term there is "learning process" - you cannot learn all the things you need to know just by asking questions here. It isn't structured enough - it won't provide you with a way to progress where each step builds on what you learned before.

You can't carry out a job of this magnitude by asking whatever random questions happen to occur to you. You've already shown that you have some dodgy misconceptions - what if you get something wrong because you have no idea your knowledge is wrong? What if you miss something because you simply have no idea it even exists, and just don't realise you don't know it?