25 Jun
2012
25 Jun
'12
4:13 p.m.
And that is soemthing else to be careful about. A friend of mine was
nearely killed by a cheap mete. He measured the voltage of a maisn
socket, it showed 240V or so, so the meter was working/ He flipped the
breaker for what he thought was the right circuit, then measured the
voltage again. 0 or so. So he thought he had isoalted the circuit and
started to remove the socket. Alas the meter had taken that momemnt to
fail (range swithc trouble I think) and he's flipped the wrong breaker.
Result : He got the mains across him. Second result, he bought a good meter.
I can't agree with this. He was not nearly killed by a cheap meter. He was
nearly killed because he did not appreciate what could go wrong. While it is
less likely to fail, a good meter can still fail. Also, if (for example) the
building was wired badly and the breaker opened the neutral, he could still
have been in trouble, even with a good meter that was working properly.
I prefer to use a neon tester for this sort of job. It doesn't need a
functional neutral or ground in order to operate and there is less to go wrong
than a meter. However, it can still go wrong and should be tested on a live
point before and after using it to identify that a circuit has been powered
off and lighting conditions must be such that the glow can be seen.
Having verified that the power is off by whatever method (and made sure someone
else could not inadvertently switch it back on), continue to take care. Do not
dive in and grab a conductor in each hand. It is often possible to treat the
circuit as if it is still live - use insulated tools, don't touch any bare
conductors and don't let any bare conductors touch each other or anything
else conductive. If it is necessary to touch a conductor, I would suggest first
brushing it with the back of a finger after ensuring there are no paths
to ground through the the other hand in particular or any other body parts in
general. Think about using a different method if you are on a high ladder.
Don't believe that using a good meter or a good anything else is all you need
to keep safe. Whatever you use, think about what could go wrong.
(If you decide to use a neon tester, make sure it is a mains rated neon tester
and not an very similar looking instrument containing a low voltage filament
bulb intended for automotive testing!)
Regards,
Peter Coghlan.
26 Jun
26 Jun
1:38 p.m.
And that is soemthing else to be careful about. A friend of mine was
nearely killed by a cheap mete. He measured the voltage of a maisn
socket, it showed 240V or so, so the meter was working/ He flipped the
breaker for what he thought was the right circuit, then measured the
voltage again. 0 or so. So he thought he had isoalted the circuit and
started to remove the socket. Alas the meter had taken that momemnt to
fail (range swithc trouble I think) and he's flipped the wrong breaker.
Result : He got the mains across him. Second result, he bought a good meter.
I can't agree with this. He was not nearly killed by a cheap meter. He was nearly killed because he did not appreciate what could
go wrong. While it is
less likely to fail, a good meter can still fail. Also, if (for example) the
building was wired badly and the breaker opened the neutral, he could still
have been in trouble, even with a good meter that was working properly.
Do a live point to local groudn test? I would.
I prefer to use a neon tester for this sort of job. It doesn't need a
functional neutral or ground in order to operate and there is less to go wrong
Well, actually,m it requires the end cap to be grounds via the user,
capacitive coupling is not enough most of the time. If you forget to
toucvh the end, or if you're not earhted yourself, it can give misleading
results. Yes, I use them, but again, you need to know what you are doing.
As I mentioend soem time back, one common use of these back in the days
of live-chassis radios and TVs was to see if the chassis was indeed live
(if som turn the plug round).. A not-funny 'joke' which could have
serious consequences was to tel lthe newbie that if he took the tester
apart and turned the neonround, it would then light on a dead chassis.
than a meter. However, it can still go wrong and
should be tested on a live
point before and after using it to identify that a circuit has been powered
off and lighting conditions must be such that the glow can be seen.
Having verified that the power is off by whatever method (and made sure someone
else could not inadvertently switch it back on), continue to take care. Do not
That is one advantage of removable fuse carries as against MCBs. You cna
remvoe the fuse and pop it in your pocket. It's a lot harder fro somevody
to find and fit a replacement fus than to accidnetally fip an MCB.
dive in and grab a conductor in each hand. It is often
possible to treat the
circuit as if it is still live - use insulated tools, don't touch any bare
AS ever, 'all wires are live until you have proved them not to be'.
conductors and don't let any bare conductors touch
each other or anything
else conductive. If it is necessary to touch a conductor, I would suggest first
brushing it with the back of a finger after ensuring there are no paths
to ground through the the other hand in particular or any other body parts in
general. Think about using a different method if you are on a high ladder.
Work one-naded if at all possible. You might also consider disconencting
the wires back at the consumer unit (fuse box) -- live and neutral -- so
there's no way the cirucit can be energised again. And check -- again --
you have the right wires disconencted.
Don't believe that using a good meter or a good anything else is all you need
to keep safe. Whatever you use, think about what could go wrong.
Indeed.
(If you decide to use a neon tester, make sure it is a mains rated neon tester
and not an very similar looking instrument containing a low voltage filament
bulb intended for automotive testing!)
Well, that's not a neon tester ;-). More seriously, yes. Do make sure you
are using the right tools and test gear, particualrly on mains and other
high-voltage circuits. It takes al ot less time to check than for your
realtives to ahve to rganise your funeral!
-tony
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