NEC 665 covers the installation of induction & dielectric heating and induction melting & welding equipment and their accessories used for industrial and scientific applications. Induction and dielectric heating use the electric or magnetic field for heating purposes in furnaces, ovens, and industrial equipment. Induction heating, melting, and welding require the heating or melting of conductive materials (metals) which generates heat due to I2R losses when the material is placed in a varying electromagnetic field. In case of the dielectric heating, dielectric heating equipment is similar to induction heating except dielectric heating is used to heat non-magnetic material. Typical applications of dielectric heating include drying textiles after dyeing, pre-heating wood fibres in the fiberboard industry, and drying water-based coatings on paper.

NEC 665.4 requires induction or dielectric heating equipment shall not be installed in hazardous locations (as referred in Article 500). If it has to be installed in hazardous locations, wiring, and equipment shall be designed and approved for hazardous locations.

NEC 665.5 requires an output circuit (external to solid state converter circuit of the heating equipment) that shall consist of components such as switches, busbars, contractors, and supply conductors. Current flowing from the output circuit to the ground during normal operation or during the ground fault condition shall limit the voltage rise to not more than 50V to the ground to appear on any accessible part of heating equipment and its load.

NEC 665.7 requires that if multiple control points are provided for the energization of the equipment, an interlock shall be provided such that the heating equipment can be energized from a single location at a time and also each control point is provided with provision to de-energize the equipment.

NEC 665.10 covers details about the ampacity calculations of the supply conductors for dielectric or induction heating equipment. The ampacity of the supply conductors supplying one or more heating equipment shall not be less than the sum of the nameplate ratings for the largest group of equipment which can operate simultaneously plus 100% of the standby currents of remaining heating equipment. If the details of the standby current of heating equipment are not available, nameplate currents shall be used. NEC 665.10(B) requires that the ampacity of conductors connecting motor-generator equipment shall be calculated in accordance with NEC 430 (Part II).

NEC 665.11 covers details about the provision of overcurrent protection for heating equipment. Overcurrent equipment shall be permitted to be provided separately or as part of the heating equipment. It shall be provided as specified in NEC 240

NEC 665.12 covers disconnecting means provisional requirement in induction or dielectric heating equipment. Disconnecting means for heating equipment shall be readily accessible from its supply circuit. It shall be capable to be locked in the open position. The rating of the disconnecting means shall not be less than the heating equipment nameplate rating. In case of only one heating equipment is supplied from the supply circuit, disconnecting means provided for the supply circuit shall be permitted to disconnect heating equipment.

NEC 665.19 states that the interconnection components required for a complete induction or dielectric heating equipment installation shall be guarded.

NEC 665.20 requires that the converting device (solid-state converter) used in heating equipment shall be completely contained within an enclosure made of noncombustible material.

NEC 665.21 requires that all control panels of heating equipment shall be of dead-front construction

NEC 655.22 covers details about access to internal equipment. Heating equipment shall be provided with access doors or detachable access paths for accessing internal equipment. These access doors to internal compartments of heating equipment operate at voltages from 150V to 1000V (either a.c or d.c) shall be capable of interlocking so that the internal compartment equipments are not energized in case of an access door in the open position. In case of the internal compartments having an operating voltage above 1000V (either a.c or d.c) access doors shall be provided with disconnecting means equipped with mechanical lockout so as to prevent access (access door is open) to internal equipment in case of equipment being in energized condition.

NEC 665.23 requires that proper warning labels or signs that read – “DANGER – HIGH VOLTAGE – KEEP OUT” shall be attached to the induction or dielectric heating equipment.

NEC 665.24 requires capacitors rated 600V nominal or below used in heating equipment shall have time and means of discharge in accordance with NEC 460.6. Similarly, capacitors rated over 600V nominal shall time and means of discharge in accordance with NEC 460.28.

NEC 665.25 requires dielectric heating applicators shall be provided with protected cages or adequate shielding. Interlock provisions shall be provided for access doors in such a manner as to remove the power supply to the applicator in case of access door opens when the applicator is in energized condition.

NEC 665.26 requires bonding connections to the equipment grounding conductor or inter-unit bondings to be provided for circuit operation so as to limit the radio frequency voltages (between all non-exposed non-current carrying parts of equipment and earth ground) to a safe value. Bonding connections and connections to equipment grounding conductor shall be in accordance to NEC 250 Parts II & V.

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