Good advice Doug. I do triple checks and am used the the rolled eyes
from "knowledgeable" people. F** em. It's less stress to do what you
suggest, and it's better advice to give.
And I am never embarrassed to have anyone check my work. No one has
never found me to make a wiring error, but if someone asked to check my
work I would say "thank you" and move over. Getting it right and safe is
cheaper than the alternative.
Usually it is the qualified engineers who recognize the value of safety
and QA checks and are never embarrassed to do the required checks, and
are never embarrassed to have someone check their work. It is part of
the training as I recall.
After a delivery truck hit a power pole and knocked down some power lines I
questioned the gentleman managing and keeping an eye on the crew repairing
the power lines. He indicated that 220 is more likely to get you as it
tends to hold on to you. The much higher voltage lines will more likely
throw you away.
On Sun, 15 May 2005 17:08:51 GMT in sci.electronics.basics, "Leon"
The dorm cafeteria where I went to college had toasters that ran on
220V. I really used to cringe when I saw people stick forks into them
to retrieve stuck pieces of toast. I guess that is routine in the UK
It's hardly _routine_ to stick forks into live toasters. Few people do
it more than once.
(Actually it's pretty safe. Only a real moron does it when they're hot
and when the power is off, the elements are isolated. Toaster makers
_know_ that there will be fools poking Darwin's Fork where they
shouldn't, and they do try to take account of this)
Cats have nine lives, which is why they rarely post to Usenet.
I've been an electrician for over 30 years and I can tell you it is
possible to get killed on 120V, but it is generally considered to be the
current that kills. As little as 100mA will cause the heart to
fibrillate regardless of voltage. It depends on the victims age,
thickness of skin (callouses insulate somewhat), how dry the skin is and
where the contact points are on the body. One older fellow I worked
with would routinely put his finger in light sockets to check for
voltage. His skin was old, dry and calloused and the current only
passed through his finger. Another who worked a circuit hot by lying on
a piece of insulating cardboard under a house died because his sweaty
neck touched a cold water pipe. Damp, thin skin, current through the
brain. Not a good combination.
GFI protection is a good thing and cheap insurance.
Several of you posters are really scaring me on this topic. If half of
you believe even bits that have been posted in this thread I don't
expect to read anything more from you within the next several months.
Benton has a chunk of the information in that 120VAC is _DANGEROUS_!!
...and yes at these voltages and frequencies (60Hz) 100mA is almost
assuredly deadly. However, under not that unusual conditions fatalities
can occur with 120VAC at currents under even 10mA! ..no you don't need
to be taking a salt-water bath as there are numerous other items that
will drop the skin resistance to permit these fatal current flows
including excessive sweating and even more so a break/burn in the skin.
A GFCI will typically cut the circuit at the 5mA ground leakage current
that is considered a manageable risk level for most conditions and
people but of course not a certainty. When I was involved in the
Electrical Safety business in Hospitals in the 70's ICU's & OR's used a
2mA alarm standard that I believe has been dropped since then into well
under the 0.5mA range to recognize the increased exposure by the lower
resistance seen in open flesh. Death can well occur at less than 100mA
at 120VAC and by numerous other factors. Treat with respect.
The GFCI works on the principle that it is able to "detect" any
_potential_ current leaks to ground. The fault current does not exist
(flow) yet but rather the devices monitors that there are defects in the
circuitry that could cause a fatal electric shock should a powered
device or line have a person be in contact with the 'failed component'-
and the safety device will shut down to prevent the actual shock
failure. There are many possible patterns that can make this condition
occur not the least being shoddy/worn insulation and broken ground wires.
For all the stories about testing live circuits with fingers and
grabbing live wires - they are not impossible nor in many cases even
risky _IF_ you fully _understand_ what you are doing and for that reason
should never be attempted by the average person.
Urban legends, hearsay and 'best guess' are not to your well being when
dealing with electricity. Get facts or leave it alone.
Yes, excessive sweating and a break in the skin can allow higher than normal
CURRENTS for a given VOLTAGE by lowering the skin RESISTANCE. (though they
are unlikely to lower the resistance of your shoes to make you grounded, and
without a ground connection, it doesn't matter how low your skin resistance
But they will not make 10ma anymore harmful. Exactly what "not that
unusual conditions" will 10ma cause fatalities? Being tied up with the
Dumbass! Such conditions will cause *much*more* than 10ma to flow! That's why
And this is why "you're* dangerous: you don't understand electricity, and yet
you continue to give "advice" about it.
Doug Miller (alphageek at milmac dot com)
Nobody ever left footprints in the sands of time by sitting on his butt.
And who wants to leave buttprints in the sands of time?
Just, for starters, EIGHT to TEN milliamps at the skin surface is sufficient
to cause seizure of the muscles, If you are grasping the live contact, you
*will*not* be able to let go of it.
That same ten milli-amps or so, _while_you_remain_in_contact_with_it_,
has all sorts of 'interesting" secondary effects. Affected musculature
is spasming -- which differs from *very* heavy exercise only in that the
muscles do not get the chance relax completely between contractions.
The body reacts to this by increasing the blood-flow to the area; by
secreting moisture to the surface of the skin, for evaporative cooling;
by migration of intra-cellular fluids into the area to provide more 'food'
for the muscle cells, etc. ALL of those things have an effect on the
resistance to the electrical current. They all _decrease_ it. Thus,
the current flow *CLIMBS*.
In addition, as the internal "chemistry" shifts around, the -path- of the
current flow changes. All skin/muscles/etc, are _not_ created equal.
Some conduct electricity better than others. "nerve cells" are especially
good conductors. As the conductivity of the body parts increases -- for
the reasons discussed in the previous paragraph -- current flow also tends
to become more 'localized'; rather than a low current flow across a wide
cross-section, you get high current in relatively small areas, and very
little current in adjacent areas. Note well that the conductivity of
those 'adjacent areas' has *NOT* decreased. The 'localization' happens
because the conductivity of those 'local' areas is *much* better.
Oddly enough, this results in increased current flow over-all, as well
as radically higher current 'density' in those 'better path' routes.
Also, effects on muscle tissue (*and* nerve fiber) depend not only on the
current flow, but *HOW*LONG* the current flows. Once you get above a very
low threshold (sub-milli-amp), degree of "injury" does increase with
continued exposure. And, of course, the higher the current flow, the
faster the 'damage' accumulates.
"Given time" 10-15 ma, *or*less*, CAN kill you. Disruption of autonomic
nervous system functions -- including heart-beat -- "slow cooking" of
nervous pathways, etc.
Remember, even at that level, if muscles spasm so that you are in contact
with the live wire, you will *NOT* get free _by_yourself_. Thus, in a
very real sense, "how quickly" things happen is not an issue. :)
When I was in tech school, one of the teachers said, "Suppose you're
working inside a transmitter chassis, and you bump up against the 12V
filament supply, get a tingle and flinch, knocking your hand into the
4KV plate supply.
"Which one killed you?"
I guess that depends on which you believe is "you". ;-)
Here's an interesting experiment. Close your eyes, and say "Me", while
simultaneously pointing at yourself. Hold that position, and open your
Where is your finger pointing?
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