INDUCTION, DIELECTRIC HEATING EQUIPMENT 70-681

665-41. Ampacity of Supply Conductors. The ampacity of supply conductors shall be determined in accordance with Article 430. 665-42. Overcurrent Protection. Overcurrent protection shall be provided as specified in Article 430 for the electric supply circuit. 665-43. Disconnecting Means. The disconnecting means shall be provided as specified in Article 430. A readily accessible disconnecting means shall be provided by which each heating equipment can be isolated from its supply circuit. The ampere rating of this disconnecting means shall not be less than the nameplate current rating of the equipment. The supply circuit disconnecting means shall be permitted as a heating equipment disconnecting means where the circuit supplies only one equipment. 665-44. Output Circuit. The output circuit shall include all output components external to the generator, including contactors, transformers, busbars, and other conductors, and shall comply with (a) and (b) below. (a) Generator Output. The output circuit shall be isolated from ground. Exception No. 1: Where the capacitive coupling inherent in the generator causes the generator terminals to have voltages from terminal to ground that are equal. Exception No. 2: Where a vacuum or controlled atmosphere is used with a coil in a tank or chamber, the center point of the coil shall be grounded to maintain an equal potential between each terminal and ground. Where rated at over 500 volts, the output circuit shall incorporate a dc ground protector unit. The dc impressed on the output circuit shall not exceed 30 volts and shall not exceed a current capability of 5 milliamperes. An isolating transformer for matching the load and the source shall be permitted in the output circuit if the output secondary is not at dc ground potential. (b) Component Interconnections. The various components required for a complete induction heating equipment installation shall be connected by properly protected multiconductor cable, busbar, or coaxial cable. Cables shall be installed in nonferrous raceways. Busbars shall be protected, where required, by nonferrous enclosures. 665-47. Remote Control. (a) Selector Switch. Where remote controls are used for applying power, a selector switch shall be provided and interlocked to provide power from only one control point at a time. (b) Foot Switches. Switches operated by foot pressure shall be provided with a shield over the contact button to avoid accidental closing of a switch. D. Equipment Other than Motor-Generator 665-60. General. Equipment other than motor-generators shall consist of all static multipliers and oscillator-type units utilizing vacuum tubes and/or solid-state devices. The equipment shall be capable of converting ac or dc to an ac frequency suitable for induction and/or dielectric heating. 70-682 NATIONAL ELECTRICAL CODE 665-61. Ampacity of Supply Conductors. The ampacity of supply conductors shall be determined in accordance with (a) and (b) below. (a) Nameplate Rating. The ampacity of the circuit conductors shall not be less than the nameplate current rating of the equipment. (b) Two or More. The ampacity of conductors supplying two or more equipments shall not be less than the sum of the nameplate current ratings on all equipments. Exception: If simultaneous operation of two or more equipments supplied from the same feeder is not possible, the ampacity of the feeder shall not be less than the sum of the nameplate ratings for the largest group of machines capable of simultaneous operation, plus 100 percent of the stand-by currents of the remaining machines supplied. 665-62. Overcurrent Protection. Overcurrent protection shall be provided as specified in Article 240 for the equipment as a whole. This overcurrent protection shall be provided separately or as a part of the equipment. 665-63. Disconnecting Means. A readily accessible disconnecting means shall be provided by which each heating equipment can be isolated from its supply circuit. The rating of this disconnecting means shall not be less than the nameplate rating of the equipment. The supply circuit disconnecting means shall be permitted for disconnecting the heating equipment where the circuit supplies only one equipment. 665-64. Output Circuit. The output circuit shall include all output components external to the converting device, including contactors, transformers, busbars, and other conductors, and shall comply with (a) and (b) below. (a) Converter Output. The output circuit shall be isolated from ground. Exception: Where a dc voltage can exist at the terminals because of an internal component failure, then the output circuit (direct or coupled) shall be at dc ground potential. (b) Converter and Applicator Connection. Where the connections between the converter and the work applicator exceed 2 feet (610 mm) in length, the connections shall be enclosed or guarded with nonferrous, noncombustible material. 665-66. Line Frequency in Converter Equipment Output. Commercial frequencies of 25- to 60-hertz alternating-current output shall be permitted to be coupled for control purposes, but shall be limited to not over 150 volts during periods of circuit operation. 665-67. Keying. Where high-speed keying circuits dependent on the effect of "oscillator blocking" are employed, the peak radio-frequency output voltage during the blocked portion of the cycle shall not exceed 100 volts in units employing radio-frequency converters.