by ericmark »
Mon Apr 11, 2016 10:11 am
No is the simple answer. Switches can get contacts welded together so although rare unless you have physically unplugged some thing then one should in theroy go through the proving dead procedure.
To prove dead first one needs to test the tester and show it is working.
Then you test the item to be proved dead.
Then you test the tester again.
In all my time as an electrician this was rare, Rock Savage chemical works is the only place this was done with low voltage (50~1000 Vac) at that works being found on the job without the tester and proving unit resulted in loss of site pass which in real terms meant you were sacked.
However with all this goody two shoes system the proving unit delivered 500 volt only and the tester had lights for 50, 100, 250 and 500 volt and what was important was that the 50 volt lamp did not light and a fault in the tester could mean at 50 volt the 50 volt light did not work but it would still work at 500 volt so the system was flawed. New proving units stage test using different voltages to show Neon does work at 50 volt.
The problem is many switches are two pole and switch both line and neutral and naughty people when one pole fails have been known to by pass one pole and if that is the line pole then light still switches on and off but is live all the time.
So in real terms I use my meter to prove dead which is not really what I should do as batteries could go flat, and as a second emergency protection I also use a neon screwdriver to detect things like borrowed neutrals. But in the main I use my skill in working out where bodgers have been working and where it is reasonable safe. And I treat all wires as live even when turned off.
