Re: [CAD_CAM_EDM_DRO] Re: wire for motor ?

turbulatordude wrote:

>--- In CAD_CAM_EDM_DRO@yahoogroups.com, cnc002@... wrote:
>
>
>>
>>In a message dated 12/10/2006 1:00:24 PM Eastern Standard Time,
>>washer@... writes:
>>
>>No.. you've made a common mistake. Wire has a given resitance per unit
>>length. This resistance will cause a heat buildup in the wire when
>>
>>
>a current flows
>
>
>>through the wire. This is why wire is rated by it's current
>>
>>
>capacity (see
>
>
>>any wire chart).
>>
>>
>
>
>Interesting. Can I then assume that a 3 amp chopper will deliver a
>constant 3 amps to the motor ? and therefore size the wire for 3
>amps ?
>
>I can see that in a holding posistion, with the driver holding one
>phase at full power (full step) the wire would experiance the highest
>amp load. any microsteps would reduce the full load to some portion
>of full.
>
>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.
>
>

This all depends on the thermal insulation over the wire, and the
maximum temperature
the electrical isulation can handle. A wire buried deep in a magnet
coil (like inside
a stepper motor) has a high thermal resistance to the outside, and so a
given current
will cause it to heat up much more than a wire suspended in mid air.
That's why
the electrical code had different specs for wire in cable, Romex,
conduit, etc.

The 9.33 A for 12 Ga is so low, it has to be meant for in a wound coil.
I have 15 A
detachable equipment cords that have 16 Ga wire in them.

Jon