Re: How not to wire up an electric grill

On Sat, 12 Jan 2008 14:20:03 -0800, ChairmanOfTheBored
<RUBored@xxxxxxxxxxxxxxx> wrote:

On Sat, 12 Jan 2008 13:52:43 -0600, John O'Flaherty <quiasmox@xxxxxxxxx>
wrote:

On Fri, 11 Jan 2008 21:09:19 -0800, ChairmanOfTheBored
<RUBored@xxxxxxxxxxxxxxx> wrote:

On Fri, 11 Jan 2008 07:28:52 -0800 (PST), Mark <makolber@xxxxxxxxx>
wrote:

On Jan 11, 3:29 am, John O'Flaherty <quias...@xxxxxxxxx> wrote:
On Thu, 10 Jan 2008 17:54:26 -0800, ChairmanOfTheBored





<RUBo...@xxxxxxxxxxxxxxx> wrote:
On Thu, 10 Jan 2008 08:57:08 -0500, Rich Webb
<bbew...@xxxxxxxxxxxxxxxxxx> wrote:

John Devereux wrote:
Robert Latest <boblat...@xxxxxxxxx> writes:

Joerg wrote:
Hello Folks,

This was posted in a German NG. Now don't do that!

http://www.linuxno.de/_data/gallery/nwl7/_medium_DSCN7823.JPG

Actually I don't think that's very dangerous. It would be dangerous if, in
the case of the power strip getting submerged, a substantial portion of the
current went through the guys' bodies but I can't see how that would happen.

Same with the old "hairdryer in bathtub" situation. What IS dangerous is
holding the dryer (or any other unsealed, mains-powered device) with wet
hands while the rest of the body is well-grounded (as it is when sitting in
the tub). What ISN'T dangerous, IMO, is to drop the plugged-in dryer into
the tub while someone is sitting in it (but not on the sink or other
grounded metal parts), especially if a FI fuse is fitted.

I couldn't bring myself to try it out to freak out the wife though (she's
convinced that 230V can arc about half a meter between blow dryers and
water), but I'm sure the biggest danger is that of an immediate divorce.

You are probably right - but perhaps the human body is a better
conductor than bath or pool water (being full of salty fluids). So the
current might take a short cut!

As I understand it, it's not a case of a short cut but that the current
flows through all available paths and a person in the bath or pool would
be part of, and well coupled to, a non-trivial subset of "all paths."

 You're both fucking wrong.

 Several MEGAVolt lightning follows many and or all paths in such a
manner as described, in SOME instances, but not some damned AC line.  It
goes to ground, and if it gets the current high enough, kicks the fucking
breaker, just like it is supposed to do.

What it does NOT do, is migrate over ten feet and pass current through a
body that does not even have an attractor for it.

What if the body is between the introduced conductor and the metal
drain pipe, connected to ground? If there is a field of some voltage
established in the water, with the tremendous wet skin surface area
removing the natural skin resistance, and the higher conductivity of
the ionic flesh, there might be significant currents throught the
body. It might only take about 100 uA through the heart to make it
fibrillate.

--
John- Hide quoted text -

- Show quoted text -

Right, there may be an Amp of current flowing directly across the
submerdged conductors and only a small amount of current flowing where
the person is, imagine the "iron filing force field lines" spreading
out like you see around a magnet. The current where the person is may
be very much smaller compared to the total current.

...BUT it takes only a very small current to hurt you.

Yes, but it also requires that the body be IN the PATH, not some lame
imaginary field lines.

Sorry, but you are thinking about it incorrectly. There isn't any
unique "the path". When there is an electric dipole in a uniformly
conductive medium (such as water), an electric field is established
that can be represented by directional lines perpendicular to
equipotential lines. Current will flow along those directional lines
in proportion to the electric field gradient there. Insertion of
something more conductive at any point will distort the field so as to
concentrate current through the more conductive area.


Take a copper cube with two attachments on opposite faces that are less
than one tenth the size of the cube. Place a silver rod that is one
tenth the cube face width in diameter over in the corner of the cube,
between the two nodes. Pass current... I'd say that the silver rod
never sees any of it.

I don't agree. You aren't going to see all the current flowing in an
infinitely narrow line between the corners- it's going to spread, and
in an even sort of way. For example, take a line between the corners
of 1 cm^2 cross-section. That will have a certain resistance. In the
next layer outward, whatever shell has an equal resistance to that
core will carry about the same current.

In any case, there's much more contrast between the conductivity of a
body full of ions and a pool full of water than between copper and
silver, even allowing for hard water and chlorine.

The two guys in the pool represent even less percentage than the rod,
AND the two nodes are NOT across the face of the pool, and the bottom of
the pool, they are across two nodes of a fucking power strip. 90% of
that pool's body of water sees ZERO current.

You don't know that both sides of the line make contact with the pool
at the same time, or with the same surface area. You don't know that
the guy smiling in the background doesn't have his wet hand lying on
the cement patio.

Even if both contacts have equal area and are centered in the pool,
there will be nowhere in the pool that actually has zero current. If
you believe in electric fields and that they have direction, then
field lines aren't imaginary.

My point is not that this situation will result in certain death, but
that it is dangerous.
--
John
.