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A transformer-type (nonmotor generator) electric arc welder has a nameplate primary current rating of 42 amperes and a marked duty cycle of 80. Ieff is not given. The multiplier that applies in this case is 0.89 from Table 630.11(A).
The minimum ampacity of the conductors for this welder is 42 x 0.89 = 37.4 amperes. Based on 60 degree C terminations, the smallest conductor size is 8 AWG which has an ampacity of 40.
Applying Section 630.12, the maximum rating of overcurrent protection for the welder is 200% x 42 = 84 amperes. The maximum rating of overcurrent protection for the conductors is 200% x 40 = 80 amperes.
A single overcurrent device rated 80 amperes would provide protection for both the 8 AWG conductors and the 42 amp welder.
© Hughes Associates,Inc. 2012