Article 665

Induction and Dielectric Heating Equipment

Part I. General

1. Scope. This article covers the construction and installa‐ tion of dielectric heating, induction heating, induction melt‐ ing, and induction welding equipment and accessories for industrial and scientific applications. Medical or dental applica‐ tions, appliances, or line frequency pipeline and vessel heating are not covered in this article.Informational Note: See Article 427, Part V, for line frequency induction heating of pipelines and vessels.
2. Definitions.

Applicator. The device used to transfer energy between the output circuit and the object or mass to be heated.

Converting Device. That part of the heating equipment that converts input mechanical or electrical energy to the voltage, current, and frequency used for the heating applicator. A converting device consists of equipment using line frequency, all static multipliers, oscillator-type units using vacuum tubes, inverters using solid-state devices, or motor-generator equip‐ ment.

Dielectric Heating. Heating of a nominally insulating material due to its own dielectric losses when the material is placed in a varying electric field.

Heating Equipment. As used in this article, any equipment that is used for heating purposes and whose heat is generated by induction or dielectric methods.

Induction Heating, Melting, and Welding. The heating, melt‐ ing, or welding of a nominally conductive material due to its own I2R losses when the material is placed in a varying electro‐ magnetic field.

1. Hazardous (Classified) Locations. Heating equipment shall not be installed in hazardous (classified) locations as defined in Article 500 unless the equipment and wiring are designed and approved for the hazardous (classified) locations.
2. Output Circuit. The output circuit shall include all output components external to the converting device, includ‐ ing contactors, switches, busbars, and other conductors. The current flow from the output circuit to ground under operat‐ ing and ground-fault conditions shall be limited to a value that does not cause 50 volts or more to ground to appear on any accessible part of the heating equipment and its load. The output circuit shall be permitted to be isolated from ground.

665.7 Remote Control.

1. Multiple Control Points. Where multiple control points are used for applicator energization, a means shall be provided and interlocked so that the applicator can be energized from only one control point at a time. A means for de-energizing the applicator shall be provided at each control point.
2. Foot Switches. Switches operated by foot pressure shall be provided with a shield over the contact button to avoid acciden‐ tal closing of a foot switch.

1. Ampacity of Supply Conductors. The ampacity of supply conductors shall be determined by 665.10(A) or (B).
   1. Nameplate Rating. The ampacity of conductors supplying one or more pieces of equipment shall be not less than the sum of the nameplate ratings for the largest group of machines capable of simultaneous operation, plus 100 percent of the standby currents of the remaining machines. Where standby currents are not given on the nameplate, the nameplate rating shall be used as the standby current.
   2. Motor-Generator Equipment. The ampacity of supply conductors for motor-generator equipment shall be deter‐ mined in accordance with Article 430, Part II.
2. Overcurrent Protection. Overcurrent protection for the heating equipment shall be provided as specified in Article240. This overcurrent protection shall be permitted to be provi‐ ded separately or as a part of the equipment.
3. Disconnecting Means. A readily accessible disconnect‐ ing means shall be provided to disconnect each heating equip‐ ment from its supply circuit. The disconnecting means shall be located within sight from the controller or be lockable open in accordance with 110.25.

The rating of this disconnecting means shall not be less than the nameplate rating of the heating equipment. Motor- generator equipment shall comply with Article 430, Part IX. The supply circuit disconnecting means shall be permitted to serve as the heating equipment disconnecting means where only one heating equipment is supplied.

Part II. Guarding, Grounding, and Labeling

1. Component Interconnection. The interconnection components required for a complete heating equipment instal‐ lation shall be guarded.
2. Enclosures. The converting device (excluding the component interconnections) shall be completely contained within an enclosure(s) of noncombustible material.
3. Control Panels. All control panels shall be of dead- front construction.
4. Access to Internal Equipment. Access doors or detach‐ able access panels shall be employed for internal access to heat‐ARTICLE 668 — ELECTROLYTIC CELLS 668.3
   ing equipment. Access doors to internal compartments containing equipment employing voltages from 150 volts to 1000 volts ac or dc shall be capable of being locked closed or shall be interlocked to prevent the supply circuit from being energized while the door(s) is open. The provision for locking or adding a lock to the access doors shall be installed on or at the access door and shall remain in place with or without the lock installed.Access doors to internal compartments containing equip‐ ment employing voltages exceeding 1000 volts ac or dc shall be provided with a disconnecting means equipped with mechani‐ cal lockouts to prevent access while the heating equipment is energized, or the access doors shall be capable of being locked closed and interlocked to prevent the supply circuit from being energized while the door(s) is open. Detachable panels not normally used for access to such parts shall be fastened in a manner that makes them inconvenient to remove.
5. 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 persons might come in contact with energized parts when doors are open or closed or when panels are removed from compartments containing over 150 volts ac or dc. The warning sign(s) or label(s) shall comply with 110.21(B).
6. Capacitors. The time and means of discharge shall be in accordance with 460.6 for capacitors rated 600 volts, nomi‐ nal, and under. The time and means of discharge shall be in accordance with 460.28 for capacitors rated over 600 volts, nominal. Capacitor internal pressure switches connected to a circuit-interrupter device shall be permitted for capacitor over‐ current protection.
7. Dielectric Heating Applicator Shielding. Protective cages or adequate shielding shall be used to guard dielectric heating applicators. 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 connec‐ ted in such a manner as to remove all power from the applica‐ tor when any one of the access doors or panels is open.
8. Grounding and Bonding. Bonding to the equipment grounding conductor or inter-unit bonding, or both, shall be used wherever required for circuit operation, and for limiting to a safe value radio frequency voltages between all exposed non–current-carrying parts of the equipment and earth ground, between all equipment parts and surrounding objects, and between such objects and earth ground. Such connection to the equipment grounding conductor and bonding shall be installed in accordance with Article 250, Parts II and V.Informational Note: Under certain conditions, contact between the object being heated and the applicator results in an unsafe condition, such as eruption of heated materials. Grounding of the object being heated and ground detection can be used to prevent this unsafe condition.
9. 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 kilovolt-amperes (kVA), and full-load power factor. Additional data shall be permitted.