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Thursday, October 6, 2016
Question:
Re: CQD answer published Wednesday, September 28, 2016 -Arc Welder
1) In the question about the single welder minimum supply conductor I am confused by your answer. You appear to state, per your calculations this welder (47.5 amp input) can be supplied by a # 12 conductor (rated at 25 amps in 75 degree column) that is supplied by a 100 amp OCPD, or a 110 amp OCPD if unnecessary opening of the overcurrent device is caused by frequent starting of the welding process. Is this correct? All based upon the heating effect of the conductor and the welder only being operated for 20% of the time, and not the load applied during the operating of the welder.
Bill Miller
2) So that arc welder will have a 100 amp breaker and the supply conductors will be #10 correct ? And thanks for keeping the code question going on,
Steve from Jersey
A
Answer:
Hey Bill and Steve from Jersey thanks for your follow up questions. The minimum conductor size based on the 21 ampere value for the welder would be 10 AWG copper from Table 310.15(B)(16) unless all terminations are listed and marked 75 degree C or higher as stated in 110.14(C).
I realize it seems strange but ampacity is based on heat and if the conductors only carry current 2 minutes out of 10 they can cool during the time there is no current. Because they are transformer welders the inrush current can be very high so the overcurrent protection is allowed to be sized much higher. This is somewhat similar to the rules for transformer protection in 450.3.