Use single-pole voltage detector to check for currentflow on a lamp
Those things detect a voltage difference between ground and the connected wire.  Your body makes the connection to ground - that's why you must touch the contact on the end of it.

The neutral wire in your house is connected to ground - the literal ground beneath your feet and the ground (green) wire in your house wiring.

There is (ideally) no voltage difference between neutral and ground.  In practice, there's usually a few (maybe a few tens) of volts difference between neutral and ground.  Not enough for the detector to notice.

There's 230V between hot and neutral, but zero between neutral and ground.

If you touch a supposed neutral wire with your detector and it lights up, then you should stop working on your wiring - there is something is wrong, and it could kill you.  If your detector lights up on a neutral wire, have your wiring checked by an electrician before you do anything else with the wiring.



The detectors are simple, and they fail "safe."  That is, if they break you will not be electrocuted while using it.

What can happen, though, is that they fail and don't detect a hot wire.

I always check the detector before doing anything on the wiring.


Turn on lights
Touch the detector to the hot wire.  It should light up.
Turn off lights.
Touch detector to the hot wire.  It should not light up.


If you touch the detector to a supposed hot wire and it doesn't light up, then you should check it again on a known good hot wire (like an outlet.)  If it still doesn't light up, it is broken.  They are cheap, buy a new one.