Hi Ped)eople
I have a query. I am a recently qualified electrician, but as always experience is gathering pace and is needed in this instance.
I have a friend who would like an extra supply from an existing rewireable fuse board which has an old (grey box) earth leakage unit between the fuse board and the meter. there are no extra places available in the fuse board and there is no isolator. I know of the notification of this work and it's usually wired in SWA. my friend wants another meter added for the extra usage.
Any and all advice is appreciated. Six sockets and lighting for the outbuilding nothing heavy..
Thanks

P:S I TRIED TO UPLOAD A PIC BUT IT SAYS ''The image must be at least 0 pixels wide, 0 pixels high and at most 1200 pixels wide and 1600 pixels high. The submitted image is 2816 pixels wide and 2112 pixels high''
i'll keep trying thanks.

To resize ...right click on the pic, select "open with" then from the additional menu "Paint"

Top left of the screen "re size"...then click on Pixels, enter a value of 1200 in the first box, the second box will change automatically..

click save...


No idea about the electrical side though..

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Verwood Handyman
I Know it says I'm On-line, but I might have just left myself logged in, whilst I'm out....

i think the pic has loaded?

I will assume a TT supply. The RCD I would expect is around the 100ma the regulations would normally want less than 300ma for fire protection. One would normally consider the RCD as being the isolator.

Likely as can't read what it says the RCD will not comply with 415.1.1 and you will need extra RCD's for any new supplies. I would consider using a new earth rod for shed but this would be dependent on the distance between shed and house.

Forgetting about regulations the problem is one does not want to under fault conditions to be able to touch two independently earthed metal parts at the same time. So items like metal soil pipes, water pipes, gas pipes can depending on design easy mean the voltage gradient can be too steep. Pets walking between the two independent earths can be in danger more than human as we have only two legs and wear shoes.

On the other hand currents running through earth cables where two systems are linked can under fault conditions become excessive and without an independent earth electrode there may not be enough current under fault conditions to operate the safety devices.

So when taking a supply to an outbuilding one has to make a judgement as to which method is appropriate for the distances and surroundings for that installation. There is no magic formula where one can say under x feet do it one way and over x feet do it another way.

However one can use the loop impedance meter to measure the likely current under fault conditions and from that reading one can make an informed decision as to what method to use.

Clearly we have no ground plans and no readings and even if we did we would all want to be on site to decide as to best method this is not something one can do remote from the site. It is far too easy to miss something vital.

So it is a case of you reading your college notes and working it out for yourself. There was a good guide on the IET website Issue 16 - Autumn 2005 of Wiring Matters see here for PDF however do remember the date this was written in 2005 so BS7671:2001 was in force not BS7671:2008 so there will be some errors with what it says.

thanks ericmark the PDF was very usefull old or not.
Jim

Dont know a deal still studying but would it not be advisable to install a new consumer unit and use the existing wireing(tested of course) and have a few spare mcb's for extra circuits rcd protected for the garage or shed?
Jim

Hi Thanks for the replies.
The out building is about 25 mts away from the house I have to confess I got confused half way through your response but the PDF was helpful.
How will a new ( additional) meter be added for the out building cheers.