ELECTRIC WELDERS

A. General 630-1. Scope. This article covers electric arc welding, resistance welding apparatus, and other similar welding equipment that is connected to an electric supply system. B. AC Transformer and DC Rectifier Arc Welders 630-11. Ampacity of Supply Conductors. The ampacity of conductors for ac transformer and dc rectifier arc welders shall be as follows: (a) Individual Welders. The ampacity of the supply conductors shall not be less than the current values determined by multiplying the rated primary current in amperes given on the welder nameplate and the following factor based upon the duty cycle or time rating of the welder. Duty Cycle (percent) 100 90 80 70 60 50 40 30 20 or less Multiplier 1.00 .95 .89 .84 .78 .71 .63 .55 .45 For a welder having a time rating of 1 hour, the multiplying factor shall be 0.75. (b) Group of Welders. The ampacity of conductors that supply a group of welders shall be permitted to be less than the sum of the currents, as determined in accordance with (a) above, of the welders supplied. The conductor rating shall be determined in each case according to the welder loading based on the use to be made of each welder and the allowance permissible in the event that all the welders supplied by the conductors will not be in use at the same time. The load value used for each welder shall take into account both the magnitude and the duration of the load while the welder is in use. ARTICLE 630 - ELECTRIC WELDERS 70-665 (FPN): Conductor ratings based on 100 percent of the current, as determined in accordance with (a) above, of the two largest welders, 85 percent for the third largest welder, 70 percent for the fourth largest welder, and 60 percent for all the remaining welders, can be assumed to provide an ample margin of safety under high-production conditions with respect to the maximum permissible temperature of the conductors. Percentage values lower than those given are permissible in cases where the work is such that a high-operating duty cycle for individual welders is impossible. 630-12. Overcurrent Protection. Overcurrent protection for ac transformer and dc rectifier arc welders shall be as provided in (a) and (b) below. Where the nearest standard rating of the overcurrent device used is under the value specified in this section, or where the rating or setting specified results in unnecessary opening of the overcurrent device, the next higher standard rating or setting shall be permitted. (a) For Welders. Each welder shall have overcurrent protection rated or set at not more than 200 percent of the rated primary current of the welder. Exception: An overcurrent device shall not be required for a welder having supply conductors protected by an overcurrent device rated or set at not more than 200 percent of the rated primary current of the welder. (b) For Conductors. Conductors that supply one or more welders shall be protected by an overcurrent device rated or set at not more than 200 percent of the conductor rating. 630-13. Disconnecting Means. A disconnecting means shall be provided in the supply circuit for each ac transformer and dc rectifier arc welder that is not equipped with a disconnect mounted as an integral part of the welder. The disconnecting means shall be a switch or circuit breaker, and its rating shall not be less than that necessary to accommodate overcurrent protection as specified under Section 630-12. 630-14. Marking. A nameplate shall be provided for ac transformer and dc rectifier arc welders giving the following information: name of manufacturer; frequency; number of phases; primary voltage; rated primary current; maximum open-circuit voltage; rated secondary current; basis of rating, such as the duty cycle or time rating. C. Motor-Generator Arc Welders 630-21. Ampacity of Supply Conductors. The ampacity of conductors for motor-generator arc welders shall be as follows: (a) Individual Welders. The ampacity of the supply conductors shall not be less than the current values determined by multiplying the rated primary current in amperes given on the welder nameplate and the following factor based upon the duty cycle or time rating of the welder. Duty Cycle (percent) 100 90 80 70 60 50 40 30 20 or less Multiplier 1.00 .96 91 .86 . 81 .75 .69 .62 .55 For a welder having a time rating of 1 hour, the multiplying factor shall be 0.80. 70-666 NATIONAL ELECTRICAL CODE (b) Group of Welders. The ampacity of conductors that supply a group of welders shall be permitted to be less than the sum of the currents, as determined in accordance with (a) above, of the welders supplied. The conductor rating shall be determined in each case according to the welder loading based on the use to be made of each welder and the allowance permissible in the event that all the welders supplied by the conductors will not be in use at the same time. The load value used for each welder shall take into account both the magnitude and the duration of the load while the welder is in use. (FPN): Conductor ratings based on 100 percent of the current, as determined in accordance with (a) above, of the two largest welders, 85 percent for the third largest welder, 70 percent for the fourth largest welder, and 60 percent for all the remaining welders, can be assumed to provide an ample margin of safety under high-production conditions with respect to the maximum permissible temperature of the conductors. Percentage values lower than those given are permissible in cases where the work is such that a high-operating duty cycle for individual welders is impossible. 630-22. Overcurrent Protection. Overcurrent protection for motorgenerator arc welders shall be as provided in (a) and (b) below. Where the nearest standard rating of the overcurrent device used is under the value specified in this section, or where the rating or setting specified results in unnecessary opening of the overcurrent device, the next higher standard rating or setting shall be permitted. (a) For Welders. Each welder shall have overcurrent protection rated or set at not more than 200 percent of the rated primary current of the welder. Exception: An overcurrent device shall not be required for a welder having supply conductors protected by an overcurrent device rated or set at not more than 200 percent of the rated primary current of the welder. (b) For Conductors. Conductors that supply one or more welders shall be protected by an overcurrent device rated or set at not more than 200 percent of the conductor rating. 630-23. Disconnecting Means. A disconnecting means shall be provided in the supply connection of each motor-generator arc welder. The disconnecting means shall be a circuit breaker or motor-circuit switch, and its rating shall not be less than that necessary to accommodate overcurrent protection as specified under Section 630-22. 630-24. Marking. A nameplate shall be provided for each motorgenerator arc welder giving the following information: name of manufacturer; rated frequency; number of phases; input voltage; input current; maximum open-circuit voltage; rated output current; basis of rating, such as duty cycle or time rating. D. Resistance Welders 630-31. Ampacity of Supply Conductors. The ampacity of the supply conductors for resistance welders necessary to limit the voltage drop to a ARTICLE 630 - ELECTRIC WELDERS 70-667 value permissible for the satisfactory performance of the welder is usually greater than that required to prevent overheating as prescribed in (a) and (b) below. (a) Individual Welders. The rated ampacity for conductors for individual welders shall comply with the following: (1) The ampacity of the supply conductors for a welder that may be operated at different times at different values of primary current or duty cycle shall not be less than 70 percent of the rated primary current for seam and automatically fed welders, and 50 percent of the rated primary current for manually operated nonautomatic welders. (2) The ampacity of the supply conductors for a welder wired for a specific operation for which the actual primary current and duty cycle are known and remain unchanged shall not be less than the product of the actual primary current and the multiplier given below for the duty cycle at which the welder will be operated. Duty Cycle (percent) 50 40 30 25 20 15 10 7.5 5.0 or less Multiplier .71 .63 .55 .50 .45 .39 .32 .27 .22 (b) Groups of Welders. The ampacity of conductors that supply two or more welders shall not be less than the sum of the value obtained in accordance with (a) above for the largest welder supplied and 60 percent of the values obtained for all the other welders supplied. (FPN): Explanation of Terms. (1) The rated primary current is the rated kVA multiplied by 1000 and divided by the rated primary voltage, using values given on the nameplate. (2) The actual primary current is the current drawn from the supply circuit during each welder operation at the particular heat tap and control setting used. (3) The duty cycle is the percentage of the time during which the welder is loaded. For instance, a spot welder supplied by a 60-hertz system (216,000 cycles per hour) making four hundred 15-cycle welds per hour would have a duty cycle of 2.8 percent (400 multiplied by 15, divided by 216,000, multiplied by 100). A seam welder operating 2 cycles "on" and 2 cycles "off" would have a duty cycle of 50 percent. 630-32. Overcurrent Protection. Overcurrent protection for resistance welders shall be as provided in (a) and (b) below. Where the nearest standard rating of the overcurrent device used is under the value specified in this section, or where the rating or setting specified results in unnecessary opening of the overcurrent device, the next higher standard rating or setting shall be permitted. (a) For Welders. Each welder shall have an overcurrent device rated or set at not more than 300 percent of the rated primary current of the welder. Exception: An overcurrent device shall not be required for a welder having a supply circuit protected by an overcurrent device rated or set at not more than 300 percent of the rated primary current of the welder. (b) For Conductors. Conductors that supply one or more welders shall be protected by an overcurrent device rated or set at not more than 300 percent of the conductor rating. 70-668 NATIONAL ELECTRICAL CODE 630-33. Disconnecting Means. A switch or circuit breaker shall be provided by which each resistance welder and its control equipment can be disconnected from the supply circuit. The ampere rating of this disconnecting means shall not be less than the supply conductor ampacity determined in accordance with Section 630-31. The supply circuit switch shall be permitted as the welder disconnecting means where the circuit supplies only one welder. 630-34. Marking. A nameplate shall be provided for each resistance welder giving the following information: name of manufacturer; frequency; primary voltage rated kVA at 50 percent duty cycle; maximum and minimum open-circuit secondary voltage; short-circuit secondary current at maximum secondary voltage; and specified throat and gap setting. E. Welding Cable 630-41. Conductors. Insulation of conductors intended for use in the secondary circuit of electric welders shall be flame-retardant. 630-42. Installation. Cables shall be permitted to be installed in a dedicated cable tray as provided in (a), (b), and (c) below. (a) Cable Support. The cable tray shall provide support at not greater than 6-inch (152-mm) intervals. (b) Spread of Fire and Products of Combustion. The installation shall comply with Section 300-21. (c) Signs. A permanent sign shall be attached to the cable tray at intervals not greater than 20 feet (6.1 m). The sign shall read "Cable tray for welding cables only."