How to confirm that an earth is an earth

[jtaunton]

Just out of curiosity.....

Many of the earth-related postings here point out that just because a plug or ceiling rose has an earth wire going to it, doesn't necessarily mean that its connected to anything at the far end.

Is there any way of checking that an earth is, in fact, earth. The only way that I can think of is to stick a multimeter between live and earth (when switched on) and see if it measuring 230v-ish (as there would be no p.d if the earth wire was just floating) but is there a way of doing a resistance check without super-long (and resistive) leads ??

 

[ban-all-sheds]

http://www.tlc-direct.co.uk/Book/8.4.1.htm

 

[mapj1]

Best method is with a meter on the 'ohms' range and a wander lead back to the main earth terminal (by the fuse board.)
Expect to read only an ohm or two more than shorting the terminalsa of the meter directly.
Or, to pass a more realistic current, a battery and low voltage lamp and wander lead (perferably something like a car side light that draws a few amps). This searches out some of the 'hanging by a thread' connections that a meter will miss.


Or, if, and only if, you are very confident it is OK, then connect a low current mains test lamp between a known live and that which is expected to be earthed, the light should come on if the earth is well connected to 0V (or the RCD should fire, if there is one protecting that circuit).
While performing this test, make sure every one stands clear of any metal fittings on that circuit, as if the earthing is not good, the test lamp will not light, or perhps light only dimly, but those things that should have been earthed will be live for the duration of the test.
This test only to be done as a 'momentary flick' test with an accomplice back at the board either briefly activating the circuit breaker or putting in and then removing the fuse.
Martindale socket testers work on this principle, and fault current meters too, but a built in timer limits the duration of the test, reducing the risk of an accidental fatality if the earthing is defective (though its still xyz painful)

I'd recommend either a meter or a battery and bulb, for the average user at least.

 

[kai]

http://www.tlc-direct.co.uk/Book/8.4.1.htm

That's a new one on me... I always thought the BS7671:2001 prescribed method is to link the Big Output terminal of the circuit's MCB to the Earth Terminals, and test with continiuity range of megger between the Red and the Earth Cores at the endmost point of the circuit. (unless a ring of course!).

 

[kendor]

Although your method with the multimeter would read a voltage if the earth has a return path it is not satisfactory as you also need to know if the earth is of a satisfactorily low impedance reading.

 

[NICEIC]

The easyest way to check if you light is earthed is by carrying out the R2 test method. All you need is a long lead and some kind of circuit tester. connect one end to you main earth by your fuse board and the other to the earth at the light. if it beeps its earthed.


N.B isolate the mains supply just in case

Ideally you should carry out an R1+R2 test , and carry out an earth loop impedance test but you would need test meters to do this.