Re: ampacity question

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

Original poster: "BunnyKiller by way of Terry Fritz <twftesla-at-uswest-dot-net>" <bigfoo39-at-telocity-dot-com>

Tesla list wrote:

> Original poster: "bob golding by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <yubba-at-clara-dot-net>
>
> Hi all,
>     I have a question about current carrying capacity of magnet wire for
> a transformer secondary. I get different ratings from different web
> sites. Father toms table says the following.
> 28 awg=0.319A
> 30 awg=0.200A
> 32 awg=0.124A
> 34awg=0.0795A
>
> Allen's home brew pig web site says
>
> 28awg=761mA
> 30awg=477ma
> 32awg=304ma
> 34awg=187ma
>
> anybody got any definitive numbers for a transformer secondary running
> under oil.?
>
> cheers
> bob golding

Hi Bob ....

the current capacity of wire is determined on several things ...   if it is
used in a
transformer application ( close wound multi layer ) a rating of 1000
circular mils is used per
amp   for other purposes ( where the wire can be "air cooled"(( air gaps
between layers)) or oil
cooled ) a rating of 500 CM per amp is feesable. For exposed air cooled
wire ( non wound) a
rating of 250 CM/A is pushing the limits.

to find circular mils of a wire....

take the wire diameter and square it ....  example ..  if the wire is
31.6/1000 th of an inch in
dia  ( 31.6 thou) approximately a #20 , this squared = 1000 CM's   this
wire would be good to
use in a close wound situation ( transformer core) with a rating of 1 amp
capacity..  using a
previous example you provided   a #34 = 6.3 thou  6.3^2 = 39.69 CM's
39.69/1000 = .039 amps
or 39mA for a transformer coil with little heat rise.( stays cool) If you
went to 750 CM/A  the
amp rating would be 53 mA.  If you dont mind a warm running coil, then
39.69/500 =  79mA. (
which is equal to your first set of data) the second set of data supplied
rates a #34 for 187
mA, this would be at the maximum rating one would want to use this wire.(
this would heat up
even in open air cooling).

TABLE

gage    thousands
awg     X/1000
18 = 40.3
19 = 35.9
20 = 32
21 = 28.5
22 = 25.3
23 = 22.6
24 = 20.1
25 = 17.9
26 = 15.9
27 = 14.2
28 = 12.6
29 = 11.3
30 = 10.0
31 = 8.9
32 = 8.0
33 = 7.1
34 = 6.3
35 = 5.6
36 = 5.0


hope this helped


Scot D