than 100 percent of the nameplate rating of the heater, provided all of the following conditions are met:
(1) The heater is marked with a minimum conductor size.
(2) The conductors are not smaller than the marked minimum size.
(3) A temperature- or pressure-actuated device controls the cyclic operation of the equipment.
(E) Conductors for Subdivided Loads. Field-wired con ductors between the heater and the supplementary overcurrent protective devices shall be sized at not less than 125 percent of the load served. The supplementary overcurrent protective devices specified in 424.72(C) shall protect these conductors in accordance with
240.4.
Where the heaters are rated 50 kW or more, the ampacity of field-wired conductors between the heater and the supplementary overcurrent protective devices shall be permitted to be not less than 100 percent of the load of their respective subdivided circuits, provided all of the following conditions are met:
(1) The heater is marked with a minimum conductor size.
(2) The conductors are not smaller than the marked minimum size.
(3) A temperature-activated device controls the cyclic operation of the equipment.
424.73 Overtemperature Limit Control. Each boiler de- signed 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 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 Overpressure Limit Control. Each boiler de- signed 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.
VIII. Electrode-Type Boilers
424.80 Scope. The provisions in Part VIII 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 V of Article 490.
424.81 Identification. Electrode-type boilers shall be iden- tified 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
210.19(A), Exception. The provisions of this section shall not apply to conductors that form an integral part of an approved boiler.
Where an electrode boiler is rated 50 kW or more, the conductors supplying the boiler electrode(s) shall be per- mitted to be sized at not less than 100 percent of the name- plate rating of the electrode boiler, provided all the following conditions