NEC 630 covers details about requirements for the provision of apparatus for electric arc & resistance welding and other welding cutting process equipment that is to be supplied by the electrical supply system.
NEC 630.11 covers about ampacity of the supply conductors for electrical arc welding equipment. NEC 630.11(A) requires that the ampacity of supply conductors connecting individual arc welders shall not be less than Ieff value as given in the rating plate. Suppose the ampacity details for supplying conductors are unavailable on the nameplate rating. In that case, the ampacity shall not be less than the rated current multiplied by the duty cycle multiplication factor as given in Table 630.11(A). NEC 630.11(B) covers power supply conductor ampacity calculations connected to the group of welders. Minimum ampacity shall be determined as per 630.11(A) and is computed as the 100% sum of the two largest welders, 85% of the third largest welder, 70% of the fourth largest welder, and 60% sum of remaining connected welders.
NEC 630.12 covers details about overcurrent protection requirements for electric arc welder conductors & equipment. NEC 630.12(A) requires that overcurrent protection for arc welder equipment shall be set not more than 200% of the maximum primary current. If the maximum primary current of the arc welder is not available, overcurrent protection shall be set not more than 200% of the rated primary current of the welder equipment. Overcurrent protection for the arc welder is not required if the same is provided at welder supply conductors rated not more than 200% of maximum current or rated primary current. NEC 630.12(B) requires that conductors supplying power to individual arc welder or group of arc welders shall be protected by an overcurrent protection device which has to be rated not less than 200% of the conductor ampacity rating.
NEC 630.13 provides details about the provisional requirements of the disconnecting means for arc welders. A disconnecting means (switch or circuit breaker) shall be provided in the supply circuit for each arc welder where it is not an integral part of the welder. Disconnecting means shall be rated not less than the overcurrent protection rating as specified.
NEC 630.14 requires that the rating plate of the arc welder shall have the following details – Name of the manufacturer, Supply frequency & phases, primary voltage, rated primary current, maximum primary current, maximum open circuit voltage, rated secondary current, and duty cycle details
NEC 630.15 covers details about the grounding of the arc welder secondary circuit. The secondary circuit (consists of electrode conductor & work conductor) of the arc welder is not treated as premises wiring and therefore is not required to be grounded (Article 250 – Grounding of separately derived systems).
NEC 630.31 provides ampacity calculation details for power supply conductors supplying power to individual or group of resistance welders. In the case of individual resistance welder which is fed automatically and operated at different values of rated primary current and duty cycle, ampacity of the supply conductors shall not be 70% of the rated primary current. If the welder is operated manually (nonautomatic welder), then the ampacity shall not be less than 50% of the rated primary current. If resistance welder is operated with constant known rated primary current and duty cycle, then the ampacity of the supply conductors shall not be less than the product of the actual primary current and duty cycle multiplication factor as given in Table 630.31(A)(2). NEC 630.31(B) requires that the ampacity of conductors supplying power to group of resistance welders shall not be less than the sum of the largest resistance welder as computed from NEC 630.31(A) and 60% of the all the welders connected.
NEC 630.32 provides details about the provision of overcurrent protection for resistance welders. 630.32(A) requires each welder shall be provided with overcurrent protection of not more than 300% of the rated primary current. A separate overcurrent protection need not be required if supply conductors to the welder are provided with overcurrent protection of not more than 200% of the rated primary current of the welder. NEC 630.32(B) requires conductors supplying one or more welders shall be provided with overcurrent protection not more than 300% of the conductor ampacity.
NEC 630.33 covers details about the provisional requirement of disconnecting means for resistance welders. A disconnecting means (switch or circuit breaker) shall be provided for each resistance welder so that it can be disconnected from the supply. The disconnecting means shall be rated not less than the supply conductor ampacity rating.
NEC 630.41 requires that the insulation provided for the welder secondary circuit shall be flame retardant
NEC 630.42 covers details about the installation of cables. Cable trays shall be provided with support at an interval not greater than 150mm (6 inches). Installation for welders shall comply with NEC 300.21 related to the spread of fire and products of combustion. Permanent signs shall be provided for Cable trays carrying welding cables at an interval not greater than 6 meters (20 feet).