Re: Electronics shielding

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "potluck by way of Terry Fritz <teslalist-at-qwest-dot-net>" <potluck-at-xmission-dot-com>

-------------------
 > Original poster: "Jim Lux by way of Terry Fritz
<teslalist-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>
 >
 >
 >
 >
 > >What I have on the drawing board is electronic control of AC
current in a
 > >main control station that will be at least 20 to 25 feet from the
coil
 > >itself  After following the advice in previous posts that leaves
the main
 > >output cable, 30 feet 4/4, as my last concern that will provide up
to 40
 > >amps to a 10Kva pig further down the line. Electronics is one thing
but
 > >electrical is quite another and that's what I'm weak in. How can I
protect
 > >that cable? I'd hate to have to buy something with shielding like
romex to
 > >handle that much current.
 >
 > Do you need real RF shielding, or just protection against mechanical
abuse
 > and the stray ground strike streamer?
 >
 > If the latter, then why not use flex metallic conduit and run your 4
wires
 > inside it.  Good mechanical protection if someone steps on it (or
drives
 > over it), and it't tough enough to take a ground strike.
 >
 > Why 4 wires to the pole transformer, by the way?  You need 2 wires
for the
 > 240VAC, presumably, and another for safety ground, but that's only
3.  Or,
 > do you have some sort of 110V load at the load end that you want to
 > supply?  (or, is it that you happen to have some 4/4 cable and want
to use
 > it...)
 >
 > Also, AWG 4 is pretty big... 10kVA at 240V is only 50Amps or so. The
NEC
 > shows AWG10 is good for 40A, and you could probably go one bump up
to AWG 8
 > for 55A.  If all 4 conductors were carrying power in your cable,
then you'd
 > need to derate a bit, also because it's jacketed, but even so, with
AWG4
 > you're paying for a lot more copper than you need.  AWG4 is twice
the
 > diameter of AWG10, and for big wire, copper cost dominates, so it
would
 > cost 4 times as much (per foot).
 >
 > You might already have your wire, in which case it's moot, but for
others
 > contemplating this sort of thing, a pair of AWG12s is equivalent to
a AWG9
 > (3 gauges is twice the area, 6 is twice the diameter), and from an
NEC
 > standpoint, two AWG12s would be 30Amps*2 = 60A (although, again, if
they're
 > run in the same raceway/conduit/etc, you'd need to derate (30%, I
 > think)).  AWG12 wire is very inexpensive due it's huge popularity.
 >
 > And of course, our TCs, particularly high power ones, are hardly
stuff that
 > is designed with NEC compliance in mind (if for no other reason than
it's
 > not a permanent installation inside a wall, where you need more
design margin).
 >
 > The real issue is going to be heating and voltage drop along the
wire.
 >
 > AWG10 is 1 ohm/1000ft, a 50 foot run puts 0.1 ohm in series (50ft
out and
 > 50ft back).  50Amps would be a 5V drop, pretty close to the 2% drop
allowed
 > by NEC for a permanent installation, and quite acceptable for a
tesla coil.
 >
 > Looking at heating.. 5V*50A is 250W, distributed along that 50 feet
of
 > wire, for 5W/ft.  This is comparable to a string of christmas
lights,
 > dissipation wise, for comparison.
 >
 > At 50A, I might feel more comfortable running a bit more than AWG10,
but I
 > don't know that AWG4 would be required...
 >
 >
 >
 >
 >

Yes, I already had the cable before my interest in TCs and never got
rid of it. I'm a hoarder and don't part with things easily. I've never
heard of flex metallic conduit and little wonder since I've never had
experience with it or need for it therefore the question of what to do
to shield it.

Thank you very much for a solution.

Rick W
salt Lake