REVISED AWG Wire Table for Coilers

From:  David [SMTP:davmckin-at-ix-dot-netcom-dot-com]
Sent:  Tuesday, April 14, 1998 2:00 AM
To:  Tesla List
Subject:  Re: REVISED AWG Wire Table for Coilers

Tesla List wrote:
> ----------
> From:  David Dean [SMTP:deano-at-corridor-dot-net]
> Sent:  Sunday, April 12, 1998 12:23 PM
> To:  Tesla List
> Subject:  Re: REVISED AWG Wire Table for Coilers
> >From:  Thomas McGahee [SMTP:tom_mcgahee-at-sigmais-dot-com]
> >Sent:  Thursday, April 09, 1998 7:59 PM
> >To:  Tesla-2; tesla-at-pupman-dot-com
> >Subject:  REVISED AWG Wire Table for Coilers
> >
> >Fellow Coilers,
> >A few people e-mailed me to say that I was a bit conservative on the amp
> >ratings
> >for the AWG wire table I e-mailed to the TESLA and TESLA-2 lists.
> >
> So what is conservative?
> In my "bible" The Handbook Of Applied Mathematics
> fourth edition copyright 1966 D. Van Nostrand Co. Inc
> there is a table for bare and enamel covered wire close wound as in a choke
> or
> transformer which gives 1500 C.M./amp. As an alternate they suggest 1000
> C.M.
> /amp.  From my own research (dissecting transformers and measuring the wire)
> I made a note on this table "real life X2" which gives 500 C. M./amp.
> In the NEC handbook (NFPA 70 1996 edition) there are many maximum ampacity
> tables but the one the electricians in the field actually use works out to
> 333 C.M./amp.
> I followed a link provided by a member of this list
> ----------
> From:  Dan Murphy [SMTP:danmurphy-at-1stnetusa-dot-com]
> Sent:  Friday, April 03, 1998 3:28 AM
> To:  Tesla-at-pupman-dot-com; tesla-2-at-emachine-dot-com
> Hello, all -
> If you are looking for ANY kind of wire, try this web site:
> http://home.sprynet-dot-com/sprynet/wiretronic
> He takes credit cards, has a toll free number, and offers a free wire info
> software program. Let us know how you fare!
> and got the free wire info software. If you look at the maximum safe current
> listed in this program, which is for magnet wire, you get more like 220
> C.M./amp.
> I use 500 C.M./amp when winding a transformer as it seems to give an
> adequate
> safyt margin and winding a transformer is quite a lot of work, done by hand.
> Best to get it right the first time.
> At any rate, I am quite pleased and thankfull for your posting of the
> original table
> as I have printed it out in large enough font to be able to read, and it is
> in the ballpark
> for my needs.
> Thanks again,
> deano
> P.S. The wire info software from Wire Tronic is in the form of a 430kb self
> executing so it does not take long to recieve and you dont need winzip or
> something like that. Also the insulation information is quite handy!

Dear David, Dan, & all,

The 1000-1500 CM / Amp is very conservative for small transformers
like the ones typically dealt with in small power supplies, etc.
And is especially conservative for oil filled transformers.  The 500 CM
Amp is a fairly typically value in the smaller power supply transformers
correlates to approximately 2546 Amps / Inch^2.  In large transformers
this value will drop to around 1000 CM / Amp or approximately 1273
These values are dependent mostly on the surface area of the coils &
the cooling ducts provided (in large transformers), and the desired
rise for the transformer, and the cooling system used.  For house wiring
I've seen all the way upto around 4000 A / in^2 or approximately 318 CM
/ A
used (I don't have the charts in front of me but these values are pretty
close - 15 A on 14 Gauge wire, 20 A on 12 Gauge wire - both of which
to the National Electrical Code).  Hope this helps.

David L. McKinnon