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NOTE: This is an unformatted excerpt from our online fire protection training library.

Special Equipment

Article 630, Electric Welders

Conductor Ampacity

Section 630.11 & Section 630.12

The conductor ampacity for an arc welder may be reduced in Section 630.11 from the full load current, based on duty cycle and a multiplier.

Then the overcurrent protection may be increased according to Section 630.12 because of the requirement to allow the arc welder to start and allow a frequent inrush current. The overcurrent protection used to protect both the welder and conductors is allowed to be rated at up to 200% of the conductor ampacity or 200% of the transformer nameplate, whichever is lower.

An informational note in Section 630.12(B) provides an equation for deriving a value for the effective heating current, based on the duty cycle operation of the welder. Different rules are provided for resistance welders.

For a sample calculation, click here.

NOTE: This is an unformatted excerpt from our online fire protection training library.

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