On 8 Oct 2007 at 23:22, Tony Duell wrote:
There is 'something to measure', namely the
voltage on the mains wiring :-)
More seriously, I see no reason why a voltmeter (analuge, digital,
whatever), used correctly -- test a known live point, test the wiring you
want to work on, test a known live point again -- is any less safe than
any other method of determining that wiring is dead.
Other than cost and fragility of the old analogue meters, you're
probably better off using something with a low number of points of
failure (a neon lamp is pretty simple). You're not interested in
*measuring* the voltage, just testing for its presence or absence.
safety checks. And always be aware that there
are lots of DIY
"fixers" out there.
So? Please rememebr that somebody doing something becuase they enjoy
doing it doesn't necessarily do a worse job that somebody who's paid to
do it. I've seen many dangerous bits of wiring done by so-called
'professionals'...
That wasn't what I meant. I mean that there are people out there who
will sneak around while you're working on a circuit and flip the
breaker on without notifying you. It's happened to me.
For safety
checking, one can use a Wiggy (still made), or a neon bulb
probe. Check for voltage before pulling the breaker and afterwards.
I don't see why those are better than a voltmeter.
Fewer parts to fail and no fuses. A genuine Wiggy not only has a
solenoid-type voltage tester; it also has a neon lamp indicator. Two
indications of current present.
Back in the 1960s there were many live-chassis valve
radios over here.
Seires stringh heaters (normally 0.1A current) and half-wave
rectification to get the HT+ line. WHich meant the chassis of the radio
was connected to one side of the mains.
...as well as hot-chassis television sets. And the US hot-chassis
radio goes back to at least the 1940s (12SA7, 12SK7, 12SQ7, 50L6,
35Z5); some of the 50's models used 7xx or 14xx loctal based tubes.
Later, the lineup was usually 12BE6, 12BA6, 12AV6, 50C5, 35W4 in
miniature envelopes.
Hot-chassis phonographs weren't that uncommon either (70L7+12SJ7) or
117L7/M7). But all of the "All American Five" sets here used a 150
ma heater string. Many of the older ones did not have polarized
mains plugs, so either side of the line could be connected to the
chassis. If there was a lot of AC hum in the audio, you were advised
to reverse the mains plug.
Equally, if you see a breaker/main switch that's
off _do not turn it on_
unless you are sure there's noe working on the circuit. But you can't
rely on that, so of course you tag/lockout the switch too.
Hence my comment about "DIY fixers". I've always wondered why
there's no sure way to secure a residential panel breaker. Panels
don't have locks and breakers look like switches with no way to tie
them down securely in the "OFF" position. It would seem that a hole
through the breaker toggle and an eyelet on the dress panel would
allow the use of a cable tie to secure the thing.
In that respect, fuses are better--you can simply remove them and
take them along with you.
Cheers,
Chuck