Shed Electrics

[Mike Goldbuyer]

Just need a bit of advice.

I have a spare socket on my main consumer unit.

It is rated at 40amp

I would like to connect up some electrics to my shed.

I have seen a small consumer unit (2 way with 6amp and 16amp)

Is this ok to run of the 40amp in the consumer unit in my house?

Lastly do I use the 6amp for lighting and the 16amp for main sockets?

I know how to wire things up but wanted to make sure I have things right.

 

[NozSpark]

Working out electric circuits is not straight forward for a lay person...

We need more info before we can properly advise you..

1. How far away from the CU is the shed?

2. What is the proposed route of the cable?

3. What is the proposed load?

4. What is the supply type?

5. What other loads do you have on the current installation?

6. Are the current services & extraneous metallic parts bonded?

7. Are there going to be and services or extraneous metallic parts in the shed?

Those questions will do for now, but I'm sure I've missed something..

 

[Mike Goldbuyer]

Hi to answer your questions in order

1, Shed is approx. 20 metres from CU

2, Through the roof, down the side in pipe attached to side of house, buried underground in pipe the up into shed.

3, load would be florescent light plus a double socket for tools and that's it

4, supply 240v

5, Current CU has 2 spare mcb slots. Already checked previously with electrician about electrics to shed and won't be overloaded.

6??

7??

 

[Andy™]

2: i hope thats not T&E in pipe. and even if its SWA, it shouldnt be in 'pipe' that could be mistaken for water etc

4: wrong answer. its either TT, TNS or TNCS. you need to know which.

6 & 7: basic questions. if you dont know this, then there is no way you could know your work is safe

whilst the job may look simple, its far from it. you would be best calling your electrician and asking him to do the job. at least you will know its done correctly & is safe

 

[apprentice87]

Hi Mike,

Please do not think members are being "awkward" Questions 4, 6, and 7, are the most important of the lot, Besides, even if you DID manage to wire it up, there is no way you have the equipment to test it. My ONE meter was about £800 for example, never mind the rest of the stuff..

Do a bit of research into questions 6 and 7, and not only will you learn a lot, but we will be able to help you more too....

john..

 

[Apache]

Question 6 refers to your incoming services - gas and water. There should be a clamp and some green/yellow (or maybe just green) wire back to the consumer unit.

Question 7 relates to any other supplies coming into the shed, so water, oil, gas etc.

Question 4 relates to the type of earthing your property has. There may be a sticker on your electricity meter saying something like 'PME'. You may have an earth rod connected back to your consumer unit and use your own earth.

Q6&7 basically are a concern because electricity flows via a gradient. Your services need to be bonded so that if they have a lower potential difference than the earth of your house you could get a shock if you were touching something earthed (say a metal toaster) and a metal water pipe - because there is a potential difference there. What is created in your house is an equipotential zone - where there is no potential difference inside the property ("equal-potential" zone). Once you start connecting things outside of this you risk introducing these potential differences in either the shed or the house.

Does that explain why these guys care?

 

[SPECIAL LOCATION]

Just need a bit of advice.

I have a spare socket on my main consumer unit.

It is rated at 40amp

I would like to connect up some electrics to my shed.

I have seen a small consumer unit (2 way with 6amp and 16amp)

Is this ok to run of the 40amp in the consumer unit in my house?

Lastly do I use the 6amp for lighting and the 16amp for main sockets?

I know how to wire things up but wanted to make sure I have things right.

Hi to answer your questions in order

1, Shed is approx. 20 metres from CU

2, Through the roof, down the side in pipe attached to side of house, buried underground in pipe the up into shed.

3, load would be florescent light plus a double socket for tools and that's it

4, supply 240v

5, Current CU has 2 spare mcb slots. Already checked previously with electrician about electrics to shed and won't be overloaded.

6??

7??

For just a fluorescent light and a double socket installing a "shed 6A/16A CU" sounds like overkill to me!!

If you did use your shed CU option you would have potentially 6A+16A load at the shed.. (22A)

In reality I would guess it will be less than 20A load !!

So if you are only going to be drawing less than 20A...

Why go to all the expense of fitting cable capable of 40A and using the 40A MCB at the house...

Thats two lots of unnecessary expense in my book..?

The cable MUST be big enough to carry any potential fault current before the MCB trips...

Otherwise the cable will melt first!!

Or to put it another way you are doing your "design" back to front...

You do not design a circuit base on what protective devices you have at the CU..

You ***** your new load requirements first....

Then consider cable size large enough to carry the load and satisfy volt drop limitations.. 

and protective device suitable to protect the cable and supply the load without any nuisance tripping etc..

I would bet that a 20A radial supply from the house to however many sockets you are fitting..

and a 3A FCU to connect the lights onto would be far cheaper......

And still give you the power you need...?

But then that is the joy of watching DIY'ers make a cheap problem expensive...

thinking they have done a good job!!

Why not ask your "electrician" that you mentioned in point 5 do give you a proper job design, install, test certify...

And not forgetting notify for Part-P compliance the new circuit you are installing!!

opcorn