How to test if single wire is live

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Sorry if this is daft but if you have a single wire visible how do you check if it's live ? I.e what do you attach the other lead of the multimeter to?
 
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The thing that you would be touching when at risk of receiving a shock. This could be the ground under your feet, the dog (under your feet), your wife, a nearby metallic thing, a nearby non-metallic thing, or, ultimately, the CPC for the circuit in question.
 
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For the first sentence, take the much-maligned neon test screwdriver, test it (and you) on a known live source, the back of a socket etc., and test the single wire. If the neon doesn't light test the screwdriver again on the known live source. You can then be reasonably sure that the wire is not live, or at least not to 230v.

For sentence two you will need to test whatever you're attaching the negative test lead to as much as the single wire. Connect the neg test lead to whatever you've chosen and connect the pos test lead to a known live source. You must get a 230v reading. Then, leaving the neg lead connected, test your single wire with the pos lead. If your reading is zero test the known live source again. Then you can be reasonably sure that the single wire is not live.
 

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