Electrical Safety

Al in Dallas · Aug 16, 2007

And if it has high current capability it can have nasty interactions
with jewelry. By brother bears a scar on his wrist from a metal watch
band that got shorted (thanks to a wrench) between a truck battery and
ground. That was just 12 volts, but it stripped the skin off his wrist
underneath the segmented metal watch band.

For some reason, instead of having a twist-lock plug and jack, we have
four separate plugs for one of our three-phase power supplies. For a
while, I would plug and unplug without turning off the source. Then, I
thought about the fact that the plug is hot when it gets part way into
the jack, and I decided to take the extra precaution of powering down
every time before plugging or unplugging.

Rich Grise · Aug 17, 2007

I work around 480V, but I've heard 12V can kill if there's enough
current available. I had to spend a whole day watching videos of
arc-flash accidents.

When I was a kid, I got my pinkie stuck on 120V. Since it was just a
trickle along one finger, it didn't hurt me, but DJ's advice is
important: "Safe" is different than "I got away with it" too - a
little current in the wrong place is fatal, especially if it has to
cross your chest to get to ground.

I still remember the day when, at about age 3, I learned to keep my thumb
out from between the prongs of the plug when I plug in the lamp. ;-)

Cheers!
Rich

John · Aug 17, 2007

I still remember the day when, at about age 3, I learned to keep my thumb
Ahhh...memories.
Like the time a outlet wall plate broke apart while my parents were
plugging something in. Naturally, they told me to stay away from the
outlets until they could buy a new plate.

Naturally, I didn't. Ouch.

John

Ross Herbert · Aug 17, 2007

Hello again from the dungeon...

As I start to get into building line-driven power supplies and such,
where should I start REALLY being careful? 40V? 60V? 110V? I realize
that current is what does the damage, but you don't have it without
voltage. (I also realize that other factors will factor).

What is the realistic neighborhood of where I shouldn't be grabbing
wires and/or switching out caps or resistors in a live circuit?

The physics and shop teacher in HS talked about 110 AC Line current
like it would knock you dead instantly. An electrician that was
installing a 208v-->480v step up transformer said "110 won't hurt you
at all. It's just enough to scare you a little bit".

I'm not about to strip a power cord and bite down on it, obviously,
but he's not the first to say 'I've been bit by 110 a bunch of times.
It's no big deal'..

Thoughts?

It depends..

In Australia, the telecommunications industry classifies 42.4Vac rms
or 60V dc as Extra Low Voltage (ELV) which is generally considered the
point where dangerous voltages commence. See page 12 ->
http://www.howtodoit.org/acif/S008_2006.pdf

Al in Dallas · Aug 18, 2007

I still remember the day when, at about age 3, I learned to keep my thumb
out from between the prongs of the plug when I plug in the lamp. ;-)

I was either plugging in or unplugging my Christmas train set. I think
I was a bit older than you. I couldn't move my finger and had to pull
away my arm, IIRC.