DIY testing earth continuity

Discussion in 'Electricians' Talk' started by Marine boy, Jan 28, 2021.

  1. Marine boy

    Marine boy Member

    I’ve just a new multimeter to replace a cheap and cheerful one that I’ve had for years. This is a fairly basic model, Kewtech 111, so no current measurement, but it has what I need, AC and DC measurement and resistance/continuity.

    I had the idea of testing all my sockets. I have a cheap socket tester which shows up any miswiring, but in addition I thought I’d check the earth continuity. So, to my mind, if I put one probe of the Kewtech on the earth terminal of the socket, and the other on a nearby light switch mounting screw, I’d be measuring the resistance of the circuit from the socket to the CU and then back via the lighting circuit to the light switch. I’ve tested all the sockets on the top floor of my 3 storey house, and the readings I’m getting are from 1 to 3 ohms, which I believe is acceptable.

    My question is - is this a viable and meaningful way of doing this or have I missed something and I’ve been wasting my time? My other idea was to run a wire (extension lead) to the earth terminal at the CU and thence to the tester and the socket, subtracting the resistance of the cable from the overall reading.
  2. Bob Rathbone

    Bob Rathbone Screwfix Select

    The wander lad that you suggest has been used for ages for initial dead testing, however, the instrument used has the ability to measure down to 0.01 ohms. and has a calibration cert. What you have will give you an idea of what's going on with CPC continuity, but cannot be used for certification, only peace of mind.
  3. Marine boy

    Marine boy Member

    Bob, yes I realise it doesn’t provide certification, but as a diyer it is peace of mind I’m after. Many thanks.
  4. The Happy Builder

    The Happy Builder Screwfix Select

    It’s a quick and easy reference, but there are better ways of doing it.
  5. Marine boy

    Marine boy Member

    Is that better as in more accurate, or easier? What I’m after is reassurance that all my sockets have a low resistance path to earth.
  6. Bazza

    Bazza Screwfix Select

    A multimeter is not going to give you any degree of accuracy especially at these low resistance levels. You need a calibrated low ohm resistance meter.
  7. The Happy Builder

    The Happy Builder Screwfix Select

    You don’t know the resistance of the lighting circuit CPC, if you used a long wander lead from the main earth terminal you could measure the resistance of the lead and deduct it to end up with the test result for the circuit you are testing.

    Just checking across between a socket and light fitting will indicate they are both earthed, but there are better ways of doing it.
  8. Marine boy

    Marine boy Member

    Thanks, that’s clear now.
  9. sparko69

    sparko69 Screwfix Select

    I wouldn't advise you to use a cheap multimeter around the area where there is 230 volts.
    You risk injuring yourself because you are not aware of the potential dangers.
  10. Marine boy

    Marine boy Member

    Thanks for that but I’m isolating the supply at the main switch.
  11. The Happy Builder

    The Happy Builder Screwfix Select

    Once the long wander lead is connected you can just go through every room in the house and test every accessible electrical fitting, such as at the screws of light switches and sockets, it’s a really quick way to find problems.
  12. The Happy Builder

    The Happy Builder Screwfix Select

    I have a Kewtech 111, I saw it at a wholesalers and thought that’s a good idea, having bought it I don’t use it much and nearly put it on EBay, at the moment it’s in the glove box of my pickup truck as I used it to check the battery :)

    You need to be aware of the issue with using any combined voltage and continuity tester that switches between reading the two or for that matter any voltage tester even a simple lamp that lights up.

    With your Kewtech 111 if you put both probes on conductors or terminals live at 240 volts it won’t give you a voltage measurement, it will give you a continuity measurement and display a resistance reading.

    So if there is an issue with the earthing and the earth conductor is at 240 volts if you try to “prove dead” it won’t give you a voltage measurement as display the resistance between them.

    Which is another good reason for using a long wander lead, so long as one end of it is connected to the main earth terminal and the main earth is in good condition the meter will display voltage measurements all the time.

    If you frequent electricians forums you will hear comments about connecting the wander lead to a long screwdriver pushed into the ground in the front lawn when the condition of the main earth is questionable, I’m not suggesting you do that, but I have had to do it.

    One incident in particular springs to mind, a complete idiot had wired a house and when rats chewed cables in the loft the testers threw up all dirts of unreliable results, which actually indicated the mains supply coming into the house had reversed polarity, which on that occasion wasn’t the issue. A long wander lead to true earth, a screwdriver in the front garden, soon showed what was what.

    You have a nice little tester in that you cannot set it to the wrong scale or test, but you do need to carefully consider the test results as there will be anomalies.
  13. Marine boy

    Marine boy Member

    Thanks Happy Builder for taking the time to explain all that, very interesting too. Some people on these forums can be quite dismissive of diyers, I like to think I have some knowledge but it’s great to hear the balanced views of professionals which is very helpful.
  14. Bazza-spark

    Bazza-spark Screwfix Select

    Comlec likes this.
  15. Marine boy

    Marine boy Member

    Yes I’ve seen that, thanks.
  16. Dave_C

    Dave_C Member

    What is the opinion on socket testers like the Kewtech Loopcheck 107 which include an Earth resistance test? It claims a resistence < 1.80 Ω will give a green light, 1.8 Ω to 92 Ω will show as orange, and greater than 93 Ω will be red.
  17. The Happy Builder

    The Happy Builder Screwfix Select

    Again, useful if you know what the test results mean.

    You will see testers like that on EBay marked as the property on British Gas, they bought them and issued them to their boiler guys, however some don’t realise that if you have TT earthing the red light is possibly an acceptable test result.

    Quite a few BG customers were told there was a potential problem with the earthing in their homes that needed an electrician to checkout, when there wasn’t anything wrong.
  18. Comlec

    Comlec Screwfix Select

    I use one when doing EICRs to check sockets. However it only assists with the process and does not replace proper circuit testing.

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