testing for earth

[gne751]

Hi everyone,
I got this device to test sockets.

Winner Mains Polarity Tester Plug: Amazon.co.uk: Electronics

Buy Winner Mains Polarity Tester Plug : Tools & Testers : Amazon.co.uk ✓ Free delivery on eligible orders

www.amazon.co.uk

I'm nearly sure that when I tested a double socket in the kitchen a few days ago, it said "no earth".
I tested the same sockets this morning and now it's saying "correct".
Is this possible?
Could they be earthed sometimes and not other times?
Is the device reliable?

 

[westward10]

I wouldn't wholly really on a cheap device like that from Amazon. It is possible the socket has a lose connection or an intermittent fault. If in doubt get a qualified person in to check them out.

 

[gne751]

If there's a better / more expensive tester you could recommend to test it myself, I'd appreciate it. If not I suppose wait for next time electrician's here.

 

[EalingBadger]

If there's a better / more expensive tester you could recommend to test it myself, I'd appreciate it. If not I suppose wait for next time electrician's here.

What Westy is saying is that the particular type of detector that you have is inherently unreliable due to the nature of the design / technique that they use and, arguably, they are at their most dangerously misleading in your current situation - i.e. a possible intermittent earth fault.

By its very nature an intermittent fault will be there sometimes and not there at other times.

A more expensive test instrument will not help at this point. Somebody that has the necessary expertise to track down the intermittent fault is what is required. If this is not you then you need to seek help from somebody that has the necessary skills.

The fault has the potential to be very quick and easy to rectify but equally well it could be tricky and subtle.

What you should not do is to ignore it now that your tester is suggesting to you that it has "gone away". To do so would be to put yourself and others at danger for the future. Don't wait for the electrician to come back. Tell him what has happened and ask him to come back.

 

[Lister1987]

I wouldn't test those devices are far as I could throw them. Biggest fault is they won't detect a N-E reverse.

Electrical Safety First (amoungst others) strongly against using them.

 

[pc1966]

Those testers are not totally useless, as in if one of them tells you there is a fault, you can be fairly sure it is bad and need to be fixed.

The danger with them is they can tell you all is OK but have not noticed a poor/high impedance earth connection, or (as mentioned above) a neutral-earth reversal (though if you have working RCD protection for your socket outlets it would notice).

So if you get any sign of a fault it should be properly investigated and fixed, but if you have any other reason to suspect an outlet (poor action of the switch, signs of cracking or thermal stress on the front plate, cracking noises from the outlet, tingling from touching anything plugged it to it, etc, etc) then don't trust an "all clear" indication from one of them.

You can get better versions that can show up a "poor" earth (rather than a non-existent one detected by the cheaper ones), but as you already have cause to get it investigated/fixed, spending another £50 on a tester will simply confirm the fault, or (actually worse) convince you it is OK when there has been pretty convincing evidence that it is suspect.

 

[gne751]

Thanks all for the advice, it makes sense. I've been living here 10 years. One of the sockets is empty, the other has a fridge-freezer plugged in (3rd in 10 years but that's probably normal these days, things not built to last).
I do remember I got a slight twinge when touched the middle, metal part of the door around a year ago... I didn't think much of it at the time, I thought it was coming from myself.
I was going to contact landlord early new year about something else, but might go ahead and contact him this week and mention this. Probably better to deal with as soon as become aware of than put it off.

 

[Wilko]

Probably better to deal with as soon as become aware of than put it off.

Absolutely .

 

[EalingBadger]

Thanks all for the advice, it makes sense. I've been living here 10 years. One of the sockets is empty, the other has a fridge-freezer plugged in (3rd in 10 years but that's probably normal these days, things not built to last).
I do remember I got a slight twinge when touched the middle, metal part of the door around a year ago... I didn't think much of it at the time, I thought it was coming from myself.
I was going to contact landlord early new year about something else, but might go ahead and contact him this week and mention this. Probably better to deal with as soon as become aware of than put it off.

You might want to suggest that he commissions an EICR.

He will have to do have done this by 1/4/2021 at the absolute very latest anyway:

Guide for landlords: electrical safety standards in the private rented sector

www.gov.uk

 

[Lucien Nunes]

Biggest fault is they won't detect a N-E reverse.

I am not sure why you consider that a fault of the plug-in tester, as there is no way any test equipment can tell the difference between two wires of unknown resistance that are connected together at the far end. How would you distinguish between them on a live circuit other than by inspection? If the wiring has different CSA for the CPC, or has parallel paths like steel containment, you might get different loop impedance readings between L-N and L-CPC and make an intelligent inference from that. The CPC would give a lower reading than neutral on MI cable but higher on T+E, etc. But on a circuit with equal CPC and a TN-C-S supply, there might be no measurable difference between the two conductors at all, so unless you trip the RCD - 'Aha that must be the neutral!' you'll be none the wiser.

I fully agree though that these testers are a menace and can be very misleading by giving a false OK when the earthing is seriously substandard.