Socket Tester Limitations

[PC Electrics]

I have a Kewtech 103 and the apprentice has my old Rapitest socket tester. Now, we all know that these devices are limited in what they can test. In particular, they are unable to detect neutral / earth reverse polarity. Well, the other day I found another limitation of these testers:

If you have 240v on both line and earth pins, they interpret this as line / neutral reversed.

Had a call from a client who had purchased a new toaster and had got a shock from the casing. He had plugged in his socket tester and it said line / neutral reversed.

So, I went and plugged mine into the toasters socket. Yep, L / N reverse. So, jumped to the [premature] conclusion that this was an open and shut case and that some ejit had miswired the socket.

(that noise you hear is a clanger hitting the floor as I whip off the socket to find the wiring is in fact perfect) :yellow card

Anyway, used the tester to check the other sockets on the circuit (this RFC serves four rooms with 18 sockets) and found a cluster of five sockets in the kitchen displaying this fault.

Using the Megger and testing voltage of pins to MET found that the five faulty sockets had 240 volts on both line and earth pins.

So, there you go. Another limitation of socket testers.

I may do another thread about the actual RFC fault.

 

[Andy™]

should post the actual fault here - more info to go with the limitations of the plug in tester

dont think ive ever had this situation with a plug in tester, but i can see why it would say L/N reverse

 

[PC Electrics]

[quote name='Andy

 

[Andy™]

Do tell, please. I'm afraid I can't see why this should be so (guess you need to know how these things work inside) because the L & N were correct.

they work on voltage difference between terminals.

you should have 230v L-N, 0V N-E, 230v L-E.

now if you were to have a 230v at earth, you now have 230v L-N, 230v N-E & 0v L-E. the important part is you would also get the exact same voltage readings here if you had L&N wrong.

live to both L&E would be very rare, especially compared to L&N crossed, and so the fault is marked as L&N reversed

basically, they only work if only 1 terminal is really live. if you have 2 terminals live, you get false readings.

also, this is where a voltage tester that doesnt need 2 points of contact to say something is live, would be useful. since you would also get the same readings on the terminals form a voltage tester, and you would assume that the neutral is 'live', but you would also get an indication something is wrong when it warns that earth or live conducor has a voltage

 

[Manator]

I never rely on voltage indicators though I do possess one, or socket testers I have two of those, I only ever use them for indication, never confirmation.

 

[PC Electrics]

Thanks Andy. It's as obvious as the nose on your face now you've explained it.

 

[orac77]

the Electrical saftey council have produced a informitive guide on the use of socket testers

 

[milojake]

Would you rate the Rapitest meter i am thinking of buying a few?