INDUCTION, DIELECTRIC HEATING EQUIPMENT 70-679

665-2. Definitions. Dielectric Heating: Dielectric heating is the heating of a nominally insulating material due to its own dielectric losses when the material is placed in a varying electric field. Heating Equipment: The term "heating equipment" as used in this article includes any equipment used for heating purposes whose heat is generated by induction or dielectric methods. Induction Heating: Induction heating is the heating of a nominally conductive material due to its own I²R losses when the material is placed in a varying electromagnetic field. 665-3. Other Articles. Wiring from the source of power to the heating equipment shall comply with Chapters 1 through 4. Circuits and equipment operated at more than 600 volts, nominal, shall comply with Article 710. 665-4. Hazardous (Classified) Locations. Induction and dielectric heating equipment shall not be installed in hazardous (classified) locations as defined in Article 500. Exception: Where the equipment and wiring are designed and approved for the hazardous (classified) locations. B. Guarding, Grounding, and Labeling 665-20. Enclosures. The converting apparatus (including the dc line) and high-frequency electric circuits (excluding the output circuits and remotecontrol circuits) shall be completely contained within an enclosure or enclosures of noncombustible material. 665-21. Panel Controls. All panel controls shall be of dead-front construction. 665-22. Access to Internal Equipment. Doors or detachable panels shall be employed for internal access. Where doors are used giving access to voltages from 500 to 1000 volts ac or dc, either door locks shall be provided or interlocking shall be installed. Where doors are used giving access to voltages of over 1000 volts ac or dc, either mechanical lockouts with a disconnecting means to prevent access until voltage is removed from the cubicle, or both door interlocking and mechanical door locks, shall be provided. Detachable panels not normally used for access to such parts shall be fastened in a manner that will make them inconvenient to remove. 665-23. Warning Labels or Signs. Warning labels or signs that read "DANGER - HIGH VOLTAGE - KEEP OUT" shall be attached to the equipment and shall be plainly visible where unauthorized persons might come in contact with energized parts, even when doors are open or when panels are removed from compartments containing over 250 volts ac or dc. 70-680 NATIONAL ELECTRICAL CODE 665-24. Capacitors. Where capacitors in excess of 0.1 microfarad are used in dc circuits, either as rectifier filter components or suppressors, etc., having circuit voltages of over 240 volts to ground, bleeder resistors or grounding switches shall be used as grounding devices. The time of discharge shall be in accordance with Section 460-6(a). Where capacitors are individually switched out of a circuit, a bleeder resistor or automatic switch shall be used as a discharge means. Where auxiliary rectifiers are used with filter capacitors in the output for bias supplies, tube keyers, etc., bleeder resistors shall be used, even though the dc voltage may not exceed 240 volts. 665-25. Work Applicator Shielding. Protective cages or adequate shielding shall be used to guard work applicators other than induction heating coils. Induction heating coils shall be permitted to be protected by insulation and/or refractory materials. Interlock switches shall be used on all hinged access doors, sliding panels, or other easy means of access to the applicator. All interlock switches shall be connected in such a manner as to remove all power from the applicator when any one of the access doors or panels is open. Interlocks on access doors or panels shall not be required if the applicator is an induction heating coil at dc ground potential or operating at less than 150 volts ac. 665-26. Grounding and Bonding. Grounding and/or inter-unit bonding shall be used wherever required for circuit operation, for limiting to a safe value radio frequency potentials between all exposed noncurrent-carrying parts of the equipment and earth ground, between all equipment parts and surrounding objects, and between such objects and earth ground. Such grounding and bonding shall be installed in accordance with Article 250. 665-27. Marking. Each heating equipment shall be provided with a nameplate giving the manufacturer's name and model identification and the following input data: line volts, frequency, number of phases, maximum current, full-load kVA, and full-load power factor. 665-28. Control Enclosures. Direct current or low-frequency ac shall be permitted in the control portion of the heating equipment. This shall be limited to not over 150 volts. Solid or stranded wire No. 18 or larger shall be used. A step-down transformer with proper overcurrent protection shall be permitted in the control enclosure to obtain an ac voltage of less than 150 volts. The higher-voltage terminals shall be guarded to prevent accidental contact. 60-hertz components shall be permitted to control high frequency where properly rated by the induction heating equipment manufacturer. Electronic circuits utilizing solid-state devices and tubes shall be permitted printed circuits or wires smaller than No. 18. C. Motor-Generator Equipment 665-40. General. Motor-generator equipment shall, include all rotating equipment designed to operate from an ac or dc motor or by mechanical drive from a prime mover, producing an alternating current of any frequency for induction and/or dielectric heating.