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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
  • 0
    IF the buildings are not yet up, put some steel re-bar grid into the footings and bring a bar out to connect to that as well - cement below DPC is not such a bad conductor, and a foundation electrode assists the electrode quite a bit.


    Testing an electrode - well, if you  hire a tester, it will inject a known voltage and read the current. . The simple tester flashes mains live onto the electrode for a short time and reads the current. The tester limits the duration and cuts off if the resistance  is too high - I do not recommend doing that without the right instrument.

    The complex testerfor when there is no supply  puts in additional electrodes and injects knowm currents and measures the voltage drop and does some cancellation to eliminate the effects of the test electrodes. "Identical" readings often vary by 25% or so -  that is just luck of the mud or weather.


    If you have access to  12V or 24V AC transformer and your meter does AC amps, you can safely get quite a long way without the official meter - put one side of the 12V to mains supply earth and the other to the electrode under test, measure the current. R = 12V/ RMS current (or 24V or whatever voltage) Do not use DC (or the meter 'ohms' ranges), electrolysis from DC causes bubbles and other polarization effects that party insulate  the surface of the electrode & confuse the results.


    Reverse the sense of the transformer (i.e. swap the output) and verify that it is more or less the same to eliminate mis readings due to any pre-extant voltage gradient in the soil from AC leakage from other users.

    if need be put in more than one rod, one rod length or more apart, and aim for a combined result of less than 100 ohms, and be smug, as the upper limit is rather higher.

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  • 0
    IF the buildings are not yet up, put some steel re-bar grid into the footings and bring a bar out to connect to that as well - cement below DPC is not such a bad conductor, and a foundation electrode assists the electrode quite a bit.


    Testing an electrode - well, if you  hire a tester, it will inject a known voltage and read the current. . The simple tester flashes mains live onto the electrode for a short time and reads the current. The tester limits the duration and cuts off if the resistance  is too high - I do not recommend doing that without the right instrument.

    The complex testerfor when there is no supply  puts in additional electrodes and injects knowm currents and measures the voltage drop and does some cancellation to eliminate the effects of the test electrodes. "Identical" readings often vary by 25% or so -  that is just luck of the mud or weather.


    If you have access to  12V or 24V AC transformer and your meter does AC amps, you can safely get quite a long way without the official meter - put one side of the 12V to mains supply earth and the other to the electrode under test, measure the current. R = 12V/ RMS current (or 24V or whatever voltage) Do not use DC (or the meter 'ohms' ranges), electrolysis from DC causes bubbles and other polarization effects that party insulate  the surface of the electrode & confuse the results.


    Reverse the sense of the transformer (i.e. swap the output) and verify that it is more or less the same to eliminate mis readings due to any pre-extant voltage gradient in the soil from AC leakage from other users.

    if need be put in more than one rod, one rod length or more apart, and aim for a combined result of less than 100 ohms, and be smug, as the upper limit is rather higher.

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