Re: [CAD_CAM_EDM_DRO] Re: wire for motor ?

In a message dated 12/10/2006 8:19:13 P.M. Central Standard Time,
dave_mucha@... writes:

In looking at the AWG charts the first thing that does not make sense is the
14 and 12ga wire. I had always assumed 12ga in a residence was good for a 20
amp servcie and 14ga was good for 15 amps.

The AWG chart shows 12ga as good for 9.33 A and 14ga as good for 5.87 A.<<
Dave: The "house wiring amps" is right. You are talking "high voltage"
(120 VAC) so a one or two volt drop is not significant for, say, 100' of wire
back to the breaker-panel (source). But for "DC Electronic stuff," especially
steppers, you are working with

quite low DC voltages, so even a 1/2 volt drop becomes a significant % of
the total.

The AWG chart you are quoting is probably for TRANSFORMER WINDING
wire-sizes. With all that many feet of wire wound up in a small wad, a relatively
small voltage-drop can cause some heat, which increases resistance, which . . .

I have built a number of small CNC lathes, plotters, and PCB drills. For
the Size 23 motors I have always used #18 stranded, even though most runs to
the drivers is only a few inches, and the currents have been less than 2 amps.
For Size 34 motors with 4 amp windings, I like #16. I did one machine with
a Size 172 motor ($$$!!!) on its X-axis, and I used #10 for that one. I
forget at the moment the exact current, but it was over 10 amps, as I recall.

A machine with almost NO voltage-drops in all the current-carrying wiring
will run noticeably healthier than one where the builder used "next best
thing". Jan Rowland


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