using multimeter to test earth

[canter]

i've not used a multimeter before but have bought one to test an earth in a light switch which I had concerns about. How would I test to make sure the earth at the switch is earthed?

 

[THRIPSTER]

Set Ohm-meter to Ohms. Put one lead on the (previously) isolated back box of the switch and the (previously) extended other lead to the Main Earth Terminal at the DB. Needless to say the circuit must be switched off to do this. You should expect to see a negligible reading. If you are not familiar with electrics and how to interpret readings from your meter I really would advise getting a professional in.



Regards

 

[fattony]

Or

Isolate the supply to the switch, put all cables in terminal block and re instate power, set your meter to AC, put one lead on the permenant Live and the other on the earth, if the earth is connected back to the consumer unit you should read 230V - 240V

 

[canter]

Thanks - and would I be right in thinking that if I do as above and connect between neutral and earth I should get 0V?

 

[Lectrician]

An earth of high impedance will give you volts.

DO as the first post says - look for low ohms. I would put one prong to the earth, and the other to a radiator, sockets earth pin, etc etc.

 

[fattony]

I assume you will be advised to go with the 1st option as its safer from a DIY point of view, maybe I should edit my post

 

[bernardgreen]

Or

Isolate the supply to the switch, put all cables in terminal block and re instate power, set your meter to AC, put one lead on the permenant Live and the other on the earth, if the earth is connected back to the consumer unit you should read 230V - 240V

NO NO

That test will NOT test the earth wire is connected in a safe way. The meter will take a few micro-amps and a high impedance path to earth will enable the meter to take the few micro-amps to show 240 volts. If the back box was in a slightly damp wall the meter would read 230 without any wire connection to earth.

That test could show a "good" earth when the earth connection was in-capable of carrying the 30 milliAmps needed to trip an RCD let alone the 32 amps needed to trip a MCB on a power circuit.

 

[securespark]

look for low ohms.

I've found some here...but while I may seem flippant, I am not making light of these images or the events that caused them.

http://www.alertnet.org/thenews/photoalbum/1104158146.htm