[QUOTE]Originally posted by doc:
[B]If you have a piece of equipment that is 220 volt single phase,and nameplate of 70 amps, and has a 100 amp breaker installed in the machine,can you hook this up to a 20 amp breaker with # 12 wire,and be legal ?
I realize that this is an old post, but I want to address the issue as best that I know how for others who may run into the same situation. If the load is a straight motor load on a branch circuit, the conductors feeding the load must be sized in accordance with 430-22 (which is 125% of the amp rating given in chart 430-148). The OCP for the branch circuit shall be sized in accordance with 430-152. If the equipment has a short time, intermittent, periodic, or varying duty cycle then you may use the chart 430-22(b) for the conductor ampacity. You'll notice that under certain conditions this chart requires that you raise the ampacity of the wire. So bear in mind that just because the equipment is not used for more than 30 seconds that the ampacity of the wire will go up (it may go down). Also remember that a "motor is to be considered to be for continuos duty unless the nature of the apparatus it drives is such that the motor cannot operate continuously with load under any condition of use (1999 NEC Handbook page 468 left side of the page)." Therefore, if there are no control devices that insure that the equipment will not run at full load for 3 hours or more, you must treat the equipment as if it were continuous. There are other issues involved here (110-14 (c), temperature, and others) from a stand point of design, that would be better addressed by an engineer. I won't bore you with the details.