FIXED ELECTRIC SPACE HEATING EQUIPMENT 70-371

shall be equipped with a temperature sensitive limiting means. It shall be installed to limit maximum liquid temperature and shall directly or indirectly disconnect all ungrounded conductors to the heating elements. Such means shall be in addition to a temperature regulating system and other devices protecting the tank against excessive pressure. 424-74. Over-Pressure Limit Control. Each boiler designed, so that in normal operation there is a change in state of the heat transfer medium from liquid to vapor, shall be equipped with a pressure sensitive limiting means. It shall be installed to limit maximum pressure and shall directly or indirectly disconnect all ungrounded conductors to the heating elements. Such means shall be in addition to a pressure regulating system and other devices protecting the tank against excessive pressure. 424-75. Grounding. All noncurrent-carrying metal parts shall be grounded in accordance with Article 250. Means for connection of equipment grounding conductor(s) sized in accordance with Table 250-95 shall be provided. H. Electrode-type Boilers 424-80. Scope. The provisions in Part H of this article shall apply to boilers for operation at 600 volts, nominal, or less, in which heat is generated by the passage of current between electrodes through the liquid being heated. (FPN): For over 600 volts see Part G of Article 710. 424-81. Identification. Electrode-type boilers shall be identified as suitable for the installation. 424-82. Branch-Circuit Requirements. The size of branch-circuit conductors and overcurrent protective devices shall be calculated on the basis of 125 percent of the total load (motors not included). A contactor, relay, or other device, approved for continuous operation at 100 percent of its rating, shall be permitted to supply its full-rated load. See Section 210-22(c), Exception. The provisions of this section shall not apply to conductors that form an integral part of an approved boiler. Exception: For an electrode boiler rated 50 kW or more, the conductors supplying the boiler electrode(s) shall be permitted to be sized at not less than 100 percent of the nameplate rating of the electrode boiler, provided all the following conditions are met: a. The electrode boiler is marked with a minimum conductor size; and b. The conductors are not smaller than the marked minimum size; and c. A temperature- or pressure-actuated device controls the cyclic operation of the equipment. 424-83. Over-Temperature Limit Control. Each boiler designed, so that in normal operation there is no change in state of the heat transfer medium, shall be equipped with a temperature sensitive limiting means. It shall be 70-372 NATIONAL ELECTRICAL CODE installed to limit maximum liquid temperature and shall directly or indirectly interrupt all current flow through the electrodes. Such means shall be in addition to the temperature regulating system and other devices protecting the tank against excessive pressure. 424-84. Over-Pressure Limit Control. Each boiler designed, so that in normal operation there is a change in state of the heat transfer medium from liquid to vapor, shall be equipped with a pressure sensitive limiting means. It shall be installed to limit maximum pressure and shall directly or indirectly interrupt all current flow through the electrodes. Such means shall be in addition to a pressure regulating system and other devices protecting the tank against excessive pressure. 424-85. Grounding. For those boilers designed such that fault currents do not pass through the pressure vessel, and the pressure vessel is electrically isolated from the electrodes, all exposed noncurrent-carrying metal parts, including the pressure vessel, supply, and return connecting piping, shall be grounded in accordance with Article 250. For all other designs, the pressure vessel containing the electrodes shall be isolated and electrically insulated from ground. 424-86. Markings. All electrode-type boilers shall be marked to show (1) the manufacturer's name; (2) the normal rating in volts, amperes, and kilowatts; (3) the electrical supply required specifying frequency, number of phases, and number of wires; (4) the marking: "Electrode-type Boiler"; (5) a warning marking - "ALL POWER SUPPLIES SHALL BE DISCON- NECTED BEFORE SERVICING, INCLUDING SERVICING THE PRESSURE VESSEL." The nameplate shall be located so as to be visible after installation. J. Electric Radiant Heating Panels and Heating Panel Sets 424-90. Scope. The provisions of Part J of this article shall apply to radiant heating panels and heating panel sets. 424-91. Definitions. (a) Heating Panel. A heating panel is a complete assembly provided with a junction box or a length of flexible conduit for connection to a branch circuit. (b) Heating Panel Set. A heating panel set is a rigid or nonrigid assembly provided with nonheating leads or a terminal junction assembly identified as being suitable for connection to a wiring system. 424-92. Markings. (1) Markings shall be permanent and in a location that is visible prior to application of panel finish. (2) Each unit shall be identified as suitable for the installation. (3) Each unit shall be marked with the identifying name or identification symbol, catalog number, and rating in volts and watts, or in volts and amperes.