Hi
The earth's magnetic field and any nearby ferrous metals too.
A typical aluminium amplifier chassis is a good shield to electrical fieldsb
ut is a very poor shield to magnetic fields.
A colleague of mine once tried to magnetically screen a switched mode
power supply and calculated a requirement for 10mm thick copper walls.
73, Mark G4AXX
>>> "Conrad G0RUZ" <conrad@g0ruz.net> 07/02/03 11:17:45 >>>
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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