When the high voltage across the room arcs, I jump too - even though there
is no connection. Of course I jump more if I am connected. I think if the
arc was big enough, I would have EMF in my pants.
K7FM
> [Original Message]
> From: Jeffrey Madore <K1LE@arrl.net>
> To: AMPS <amps@contesting.com>
To: <amps@contesting.com>
> Date: 2/7/03 11:33:24 AM
> Subject: Re: [Amps] Re: Voodoo "EMF' forces from grid current pulses
>
> I used to wonder if the attraction to the earth's magnetic field was a
> plausible explanation to the jumping cables. I came to the belief that it
is
> not, as the earth's field is not that strong at any given location. For
> example, I have a mag mount that is so strong that I need to use two hands
> and considerable force to apply it to the roof of my van, lest I cause
body
> damage. The magnet is not noticeably attracted to earth. A magnetic
compass
> needle is very light yet it's reaction to the earth's field is not
> particularly violent. In fact, it will happily point to the barrel of my
> rifle if I'm not careful.
>
> As far as shielding, enclosures, etc. I see those as possibly enhancing
> magnetic / mechanical forces caused by a high current pulse within the
> shielded area. Aluminum makes a great magnet.
>
> I used to do a classroom / lab demonstration where I would remove the
rotor
> from a 2hp 3 phase motor and place an aluminum can in the stator. Most
> students (all adult engineering, electricians, test specialists, etc)
would
> guess that the stator's field would not have any effect on the aluminum
can,
> as it was non ferrous. I would then energize the stator and the can would
> spin so fast that it would shoot out of the end of the stator. People were
> then willing to understand that the aluminum bars cast within the iron of
> the rotor, were the cause of magnetic action (through induction) and
torque.
>
> I say all that to get back to inductance and transformer theory: When an
AC
> current flows in a conductor (primary) it causes a changing magnetic
field
> which induces a potential in anything conductive (secondary), that is
within
> the effects of that field.
>
> If there is an electrical circuit, current will then flow in the
secondary.
> In the case of the aluminum can, these were circulating currents. Now, the
> secondary current is nearly 180 degrees out of phase with the current in
the
> primary, thus the magnetic field produced by the secondary current is also
> out of phase with the primary's field. This leads to maximum mechanical
> forces.
>
> So, could a large current flow between two elements within a vacuum tube,
> cause mechanical distortion of other fragile elements within that tube? I
> believe so.
>
> 73, Jeff - K1LE - CT ><>
>
>
> ----- Original Message -----
> From: "Conrad G0RUZ" <conrad@g0ruz.net>
> To: " AMPS" <amps@contesting.com>
> Sent: Friday, February 07, 2003 6:17 AM
> Subject: RE: [Amps] Re: Voodoo "EMF' forces from grid current pulses
>
>
> > This can be easily explained, the welding cables are subject to the
earths
> > magnetic field and any other localised magnetic fields, that's why they
> jump
> > about. The question is, would this happen in a shielded enclosure (amp
> > chassis) and with the magnitude of current flowing in the grid during a
> > fault condition? I am still sceptical. One thing's for sure, something
> > happens, but what?
> >
> > 73
> >
> > Conrad G0RUZ
> >
> > -----Original Message-----
> > From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]On
> > Behalf Of Jeffrey Madore
> > Sent: 07 February 2003 04:24
> > To: 2; MorgusMagnificen@aol.com; AMPS
> > Subject: Re: [Amps] Re: Voodoo "EMF' forces from grid current pulses
> >
> >
> >
> > >
> > > >I strongly challenge this assertion. I know of no mechanism within
the
> > realm
> > > >of classical EM field theory to account for this. I am assuming you
are
> > > >referring to the normal force that would accompany two
current-carrying
> > > >conductors which are in parallel proximity to each other.
> > > >
> > > Have you ever been to a welding shop and observed what happens to
> > > arc-welder cables when an arc is struck? I have and I saw the cables
> > > jump about on the floor.
> >
> > Yea verily, Rich!
> >
> > In my past life I did high current trip testing on 480 volt circuit
> > breakers. 50,000 amps was not unusual but even much lower currents would
> > make welding cables jump off of the floor.
> >
> > I remember experimenting with a fairly large 480/120 3 phase lighting
> > transformer, with a dead short on the secondary and 208 volts applied to
> the
> > primary via a pretty large motor control contactor and momentary push
> > button. It was a "hit the button while peaking around the corner" type
of
> > experiment. We were able to draw about 2000 amps momentarily on the
> > secondary which really made a set of welding cables jump.
> >
> > In my experience, a single conductor doesn't need any other conductor
near
> > it to display mechanical force when high current is applied. The self
> > inductance of the cable and resulting cemf produce sufficient magnetic
> > reaction to make the cable jump if it is not secured. Very interesting
to
> > look at the Z of a 4/0 welding cable...
> >
> > I've often found that if our engineering theories couldn't explain what
> > appeared to take place in reality, then we needed to look deeper into
the
> > matter.
> >
> > 73, Jeff - K1LE - CT
> >
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>
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--- COLIN LAMB
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