Calculating Arc Welders and Resistance Welders
How to Calculate Arc Welders and Resistance Welders per the 2023 National Electrical Code
Arc Welders
The procedure for determining conductor size for arc welders is found in 630.11. To determine the current the conductors, multiply the primary current rating listed on the nameplate of the welder by the duty cycle factor that is found in Table 630.11(A).
Once the current of the conductors is found in amps, use Table 310.16 to size the conductors. The procedure for determining overcurrent protection for arc welders is found in 630.12. Overcurrent protection for arc welders is determined by multiplying the primary current by 200%. If the OCPD does not correspond to a standard size, the next lower standard sized OCPD should be used.
Resistance Welders
The procedure for determining conductor size for resistance welders is found in 630.31. To determine the current of the conductors, multiply the primary current rating listed on the nameplate of the welder by the duty cycle factor that is found in Table 630.31(A). Once the current of the conductors is found in amps, use Table 310.16 to size the conductors.
The procedure for determining overcurrent protection for resistance welders is found in 630.32. Overcurrent protection for resistance welders is determined by multiplying the primary current by 300%. If the OCPD does not correspond to a standard size, the next higher standard size OCPD should be used.
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