Body & Soul0 min ago
This Is Why You Never Trust ...
18 Answers
... a "mains tester" screwdriver.
I'm doing some continuity testing in my new house - there are some blanked off mains outlets in the conservatory & I want to fit some lights.
So - I want to know which (if any) wall switch controls the supply to the blanked off outlets.
Which means working 'live' - unless I beg/borrow some professional kit.
I'm a very cautious person (albeit a reasonably knowledgable one) when it comes to electrics - belt, braces and a spare pair of pants is the rule - but it is a helluva sight easier to test for mains voltage with a mains tester screwdriver than piddle around with my multimeter.
So :
1. I check that the neon in the tester is working (with a known live source) - nice bright glow.
2. I check the outlet with the possible switch in both positions - not a sausage - dead as a dead thing that's quite dead.
Which (to the average person - who has probably skipped part 1 above anyway) says - this is not live and you can have a good prod around to see what's going on.
But (being me) - I go back to the known live and recheck the tester - which emits no a photon of glow - nada, zilch.
So I get the multimeter out and (lo and behold) a nice fat 240v at both my known live source AND the outlet I was testing.
The neon had randomly failed between me testing it and using it for real ...
... which is today's "phew" moment.
cautious and still sunny dave
I'm doing some continuity testing in my new house - there are some blanked off mains outlets in the conservatory & I want to fit some lights.
So - I want to know which (if any) wall switch controls the supply to the blanked off outlets.
Which means working 'live' - unless I beg/borrow some professional kit.
I'm a very cautious person (albeit a reasonably knowledgable one) when it comes to electrics - belt, braces and a spare pair of pants is the rule - but it is a helluva sight easier to test for mains voltage with a mains tester screwdriver than piddle around with my multimeter.
So :
1. I check that the neon in the tester is working (with a known live source) - nice bright glow.
2. I check the outlet with the possible switch in both positions - not a sausage - dead as a dead thing that's quite dead.
Which (to the average person - who has probably skipped part 1 above anyway) says - this is not live and you can have a good prod around to see what's going on.
But (being me) - I go back to the known live and recheck the tester - which emits no a photon of glow - nada, zilch.
So I get the multimeter out and (lo and behold) a nice fat 240v at both my known live source AND the outlet I was testing.
The neon had randomly failed between me testing it and using it for real ...
... which is today's "phew" moment.
cautious and still sunny dave
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You can trust them. If the neon lights, it's live. If it doesn't light it may or may not be live. What's there not to trust ?
Meters can be misleading too. Never put a probe on to read nothing and you are convinced there is nothing and then a slight movement makes a better contact and the meter flips to max ?
Test and check again.
Meters can be misleading too. Never put a probe on to read nothing and you are convinced there is nothing and then a slight movement makes a better contact and the meter flips to max ?
Test and check again.
Svejk:
The trick with the 'finger test' is actually to use the back of your hand. If the circuit's live, the shock makes you close your fingers, forcing them away from the power source.
I've worked on live power circuits (domestically, on stage lighting and inside TV and radio sets) many times and I've also connected myself to the mains many times. It certainly hurts a bit but I still seem to be here!
However the biggest zap I've ever received (which through me across the room) was a faulty klystron oscillator when I was in the 6th form at school.
The trick with the 'finger test' is actually to use the back of your hand. If the circuit's live, the shock makes you close your fingers, forcing them away from the power source.
I've worked on live power circuits (domestically, on stage lighting and inside TV and radio sets) many times and I've also connected myself to the mains many times. It certainly hurts a bit but I still seem to be here!
However the biggest zap I've ever received (which through me across the room) was a faulty klystron oscillator when I was in the 6th form at school.
Dave.......hit the screwdriver as hard as possible with a big hammer...and chuck it in the bin.These things can be lethal..especially if they get dropped in water.The resistor shorts out and you get a mains voltage 'experience'. Buy a voltage tester with a decent name on it..Fluke..Megger..etc......and learn how to use it.
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