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DIY domestic wiring to outbuildings

Former Community Member
Former Community Member
Hello, I am new to the forums and would like to introduce myself. In the past I have undertaken a lot of domestic wiring as a DIYer. Most of this predated the Part P requirements. However, in 2013 I undertook a fairly major wiring project at my home that included two new consumer units and half a dozen or so circuits. I did this under building control and they arranged inspection and testing. I secured a full set of certificates to underpin my work. I am about to go through the same process to add in two outbuildings to my set up. I have submitted a building notice and am awaiting to hear from Building Control re appointment of a firm to undertake inspection and testing.

Whilst I gather most DIY work scares many of you you, worth pointing out that whilst I am not any form of electrical Engineer, I do have (from many years ago) a HND in Mechanical and Production Engineering and a B Eng (Hons) in Engineering Technology. Both of these included a significant element of electrical technology and electronics. I have also worked in engineering (aerospace) for much of of my early career and still work in a STEM environment. Further,  intend to do a short course on the latest regulations and may also undertake a C&G course on testing and inspection to possibly get to a point where I can register with one of the governing bodies.

I have come to this forum as I am designing my changes and preparing for the first fix. i have been seeking guidance on the internet and from the regulations themselves. I find the regulations open to many interpretations and the advice on many forums to be wildly different. I really want to get this installation right and will have many questions, most requiring practical experience that I simply do not have. I believe this forum will be able to guide me in the right direction when I need it.


My first question relates to burial of SWA. I had a digger in last week to put in a series of trenches for cables. I intend to do all of the external wiring in SWA and in an ideal world would have buried it at 600mm. However, I have places in the garden where it is not possible to get that deep. For an example, under one lawn I have an underground structure that limits the trench depth to 300mm. What would be a appropriate method for installing SWA at this depth? Do I need to add something to prevent a spade/fork penetrating the cable, if so, what would you recommend? I also need to watch my budget here so looking for cost effective views if possible.


There will be further questions. Thank you.


regards

Parents
  • Former Community Member
    0 Former Community Member
    Thanks all for replies so far. I like the idea of a hard slab like material above the cable, do you think my BC employed inspector will? I have seen that you can still buy cable tiles, just quite expensive. I do believe 300mm to be within spade/fork depth but agree that a piece of robust slab with warning tape above should reduce risk to almost insignificant. The option of going around the obstruction to avoid areas that may be dug in the future is extremely difficult if not impossible. The cable will be a  distribution circuit and be in 16mm SWA. The armour and the third core will be connected to the house earth to protect the cable, this will not be continued beyond the cable end. The house is TNCS, the outbuilding will be a TT installation with a (is one enough?) earth spike. 


    Which brings me onto another question, is a single earth spike in chalk a good enough earth? How would I test it when I only have access to a multimeter? If when tested by the BC inspector, it fails, it will cost me for a full retest. I am trying to avoid that. It cost me an additional £400 last time down to silly errors that I could have easily avoided.
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  • Former Community Member
    0 Former Community Member
    Thanks all for replies so far. I like the idea of a hard slab like material above the cable, do you think my BC employed inspector will? I have seen that you can still buy cable tiles, just quite expensive. I do believe 300mm to be within spade/fork depth but agree that a piece of robust slab with warning tape above should reduce risk to almost insignificant. The option of going around the obstruction to avoid areas that may be dug in the future is extremely difficult if not impossible. The cable will be a  distribution circuit and be in 16mm SWA. The armour and the third core will be connected to the house earth to protect the cable, this will not be continued beyond the cable end. The house is TNCS, the outbuilding will be a TT installation with a (is one enough?) earth spike. 


    Which brings me onto another question, is a single earth spike in chalk a good enough earth? How would I test it when I only have access to a multimeter? If when tested by the BC inspector, it fails, it will cost me for a full retest. I am trying to avoid that. It cost me an additional £400 last time down to silly errors that I could have easily avoided.
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