[TowerTalk] Voltage Breakdown For Enameled Wire

Jim Thomson jim.thom at telus.net
Tue Jan 30 11:37:20 EST 2018

Date: Sun, 28 Jan 2018 18:02:55 -0800
From: Jim Brown <jim at audiosystemsgroup.com>
To: towertalk reflector <towertalk at contesting.com>
Subject: [TowerTalk] Voltage Breakdown For Enameled Wire

<I'm once again considering winding high power chokes with enameled wire. 
Zo of a closely #12 pair is about 53 ohms, which makes it desirable IF 
breakdown voltage is sufficient. I would appreciate for sources of #10 
or #12 enameled wire with published breakdown specs.

I've found that THHN (about 93 ohms Zo) works fine for simple antennas 
like dipoles, but some multiband antennas with complex matching/coupling 
systems don't like that much mismatch. We had this problem with the 
Force 12 C3SS, the choke is enameled #12 of unknown pedigree. No 
breakdown issues with a 600W power amp and the antenna is a good match 
to it, but the engineer in me wants to be conservative for legal limit 
to an 80/75 dipole that I use from 3.5-3.9 MHz.

Yes, I know I could put the conductors in Teflon tubing, but that 
increases Zo. I've measured #12 pairs with various Teflon insulation and 
get values around 101 ohms at HF.


73, Jim K9YC

##  I bought a bunch of 10 gauge and also 8 gauge  from SSON, on sale,
years ago.  It used polyimide.  Was rated for  15 kv, at least in the larger gauges,
like  14-12-10-8.    V rating was reduced with the smaller gauges, since if  15 kv
insulation used on real small stuff, like   18-28 gauge wire, then the insulation  would be super
thick compared to the actual  small gauge wire diameter itself...and  28 gauge wire would resemble
something like 20 gauge wire.   

##  In  Orrs very last handbook, the blue covered one, they had a chart at the back of the book, showing
3 different  diameters for the SAME  gauge magnet wire.   The difference  between the 3 was the thickness
of the insulation used.    This can have a profound effect when winding plate chokes for tube amps, and explains
why 2 identical wound chokes  can have series resonances on  different freqs.   The turns per inch was less
when the thicker insulation was used. 

##  The stuff I bought hi pot tested to > 15 kv.  And  >  30 kv between  adjacent turns.   If you really want to go crazy,
you can slide it into teflon tubing, but as you stated, for your application, Zo increases too much.   For my application,
I was just using it for bifilar fil chokes..and the  15 kv rating was gross overkill anyway, but at the time, the price was right.

##  What ever you end up buying, easy enough to hi pot test it, which is typ done at  DC..or  60 hz  AC. 

Jim   VE7RF 

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