(a) Each automatically fired steam or vapor-system boiler shall have an automatic low-water fuel cutoff so located as to automatically cut off the fuel supply before the surface of the water falls below the lowest visible part of the water gage glass. If a water feeding device is installed, it shall be so constructed that the water inlet valve cannot feed water into the boiler through the float chamber and so located as to supply requisite feedwater.
(b) Such a fuel cutoff or water feeding device may be attached directly to a boiler. A fuel cutoff or water feeding device may also be installed in the tapped openings available for attaching a water glass direct to a boiler, provided the connections are made to the boiler with nonferrous tees or Y's not less than NPS ½ (DN 15) between the boiler and the water glass so that the water glass is attached directly and as close as possible to the boiler; the run of the tee or Y shall take the water glass fittings, and the side outlet or branch of the tee or Y shall take the fuel cutoff or water feeding device. The ends of all nipples shall be reamed to full-size diameter.
(c) Fuel cutoffs and water feeding devices embodying a separate chamber shall have a vertical drain pipe and a blowoff valve not less than NPS ¾ (DN 20), located at the lowest point in the water equalizing pipe connections so that the chamber and the equalizing pipe can be flushed and the device tested.
HG-607 MODULAR STEAM HEATING BOILERS
(a) Each module of a modular steam heating boiler shall
be equipped with
(1) steam gage, see HG-602
(2) water gage glass, see HG-603
(3) a pressure control that will cut off the fuel supply when the pressure reaches an operating limit, which shall be less than the maximum allowable pressure
(4) low water cutoff, see HG-606
(b) The assembled modular steam boiler shall also be equipped with a safety limit control that will cut off the fuel supply to prevent steam pressure from exceeding the 15 psi (100 kPa) maximum allowable working pressure of the boiler. The control shall be constructed to prevent pressure setting above 15 psi (100 kPa).
HG-610 FOR HOT WATER HEATING OR HOT WATER SUPPLY BOILERS
HG-611 PRESSURE OR ALTITUDE GAGES
(a) Each hot water heating or hot water supply boiler shall have a pressure or altitude gage connected to it or to its flow connection in such a manner that it cannot be shut off from the boiler except by a cock with tee or lever handle, placed on the pipe near the gage. The handle of the cock shall be parallel to the pipe in which it is located when the cock is open.
(b) Mechanical Gages (Analog). The scale on the dial of the pressure or altitude gage shall be graduated to not less than 1½
nor more than 3½ times the pressure at which the safety relief valve is set.
(c) Electronic gages used in lieu of mechanical gages shall meet the following requirements:
(1) Gage shall be powered from the boiler power supply and it shall have a display that remains on at all times. The gage shall have a backup power supply.
(2) The full scale range of the transducer must be a minimum of 1½ times the pressure at which the safety relief valve is set. It shall be accurate to within ±2% of full scale.
(3) The transducer shall have a media compatibility of both liquids and gases and be temperature compensated.
(4) The gage shall have an operating temperature range of 32°F to 250°F (O°C to 120°C) unless otherwise required by the application.
(d) Piping or tubing for pressure- or altitude-gage connections shall be of nonferrous metal when smaller than NPS 1 (DN 25).
HG-612 THERMOMETERS/TEMPERATURE
SENSORS
Each hot water heating or hot water supply boiler shall have a thermometer or temperature sensor with display so located and connected that it shall be easily readable. The thermometer or sensor shall be so located that it shall at all times indicate the temperature of the water in the boiler at or near the outlet.
(a) Thermometer shall have a minimum full scale range of 5O°F to 250°F (10°C to 120°C).
(b) Electronic temperature sensor used in lieu of a thermometer shall meet the following requirements:
(1) The sensor shall be powered from the boiler power supply and it shall have a display that remains on at all times. The gage shall have a backup power supply.
(2) The full scale of the sensor and display must be a minimum of 250°F (120°C). It shall be accurate to within: ±1 deg.
(3) The sensor shall have a minimum operating temperature range of 32°F to 300°F (0°C to 150°C).
(4) The display shall have an ambient operating temperature range of 32°F to 120°F (0°C to 50°C) unless otherwise required by the application.
HG-613 TEMPERATURE CONTROL
Each automatically fired hot water heating or hot water supply boiler shall be protected from over-temperature by two temperature-operated controls.
(a) Each individual automatically fired hot water heating or hot water supply boiler shall have a high temperature limit control that will cut off the fuel supply to prevent water temperature from exceeding its marked maximum water temperature at the boiler outlet. This control shall be constructed to prevent a temperature setting above the maximum.
(b) Each individual hot water heating or hot water supply boiler shall have a control that will cut off the fuel supply when the system water temperature reaches a preset operating temperature, which shall be less than the maximum water temperature.
HG-614 LOW-WATER FUEL CUTOFF
(a) Each automatically fired hot water boiler with heat input greater than 400,000 Btu/hr (117 kW) shall have an automatic low-water fuel cutoff that has been designed for hot water service, and it shall be so located as to automatically cut off the fuel supply when the surface of the water falls to the level established in (b) below (see Fig. HG-703.2).
(b) As there is no normal waterline to be maintained in a hot water boiler, any location of the low-water fuel cutoff above the lowest safe permissible water level established by the boiler manufacturer is satisfactory.
(c) A coil-type boiler or a watertube boiler with heat input greater than 400,000 Btu/hr (117 kW) requiring forced circulation to prevent overheating of the coils or tubes shall have a flow-sensing device installed in lieu of the low-water fuel cutoff required in (a) above to automatically cut off the fuel supply when the circulating flow is interrupted.
(d) A means shall be provided for testing the operation of the external low-water fuel cutoff without resorting to draining the entire system. Such means shall not render the device inoperable except as described as follows. If the means temporarily isolates the device from the boiler during this testing, it shall automatically return to its normal position. The connection may be so arranged that the device cannot be shut off from the boiler except by a cock placed at the device and provided with a tee or lever-handle arranged to be parallel to the pipe in which it is located when the cock is open.
HG-615 MODULAR HOT WATER HEATING
BOILERS
(a) Each module of a modular hot water heating boiler shall be equipped with
(1) pressure/altitude gage, see HG-611
(2) thermometer, see HG-612
(3) temperature control that will cut off the fuel supply when the temperature reaches an operating limit, which shall be less than the maximum allowable temperature
(b) The assembled modular hot water heating boiler shall also be equipped with
(1) a safety limit control that will cut off the fuel supply to prevent the water temperature from exceeding the maximum allowable temperature at the boiler outlet. The control shall be constructed to prevent a temperature setting above the maximum. This control shall be located within 3 ft. (1.0 m) of the fitting connecting the last module to the heating supply piping.
(2) low water fuel cutoff, see HG-614.
HG-620 FOR ALL BOILERS
HG-621 INSTRUMENTS, FITTINGS, AND
CONTROLS MOUNTED INSIDE BOILER JACKETS
Any or all instruments, fittings, and controls required by these rules may be installed inside of boiler jackets provided the water gage on a steam boiler is accessible without the use of tools and provided the water gage and pressure gage on a steam boiler or the thermometer and pressure gage on a water boiler are visible through an opening or openings at all times.
HG-630 ELECTRIC WIRING
HG-631 ELECTRICAL CODE COMPLIANCE
All field wiring for controls, heat generating apparatus, and other appurtenances necessary for the operation of the boiler or boilers should be installed in accordance with the provisions of the National Electric Code and/or should comply with the applicable local electrical codes. All boilers supplied with factory mounted and wired controls, heat generating apparatus, and other appurtenances necessary for the operation of the boilers should be installed in accordance with the provisions of the nationally recognized standards such as listed in footnote 2 [17]of HG-640.
HG-632 TYPE CIRCUITRY TO BE USED
Whether field or factory wired, the control circuitry shall be positively grounded and shall operate at 150 V or less. One of the two following systems may be employed to provide the control circuit.
(a) Two-Wire Nominal 120 V System With Separate Equipment Ground Conductor
(1) This system shall consist of the line, neutral, and equipment ground conductors. The control panel frame and associated control circuitry metallic enclosures shall be electrically continuous and be bonded to the equipment ground conductor.
(2)
The equipment ground conductor and the neutral conductor shall be bonded together at their origin in the electrical system as required by the NEC.
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(3) The line side of the control circuit shall be provided with a time delay fuse sized as small as practicable.
(b) Two-Wire Nominal 120 V System Obtained By Using an Isolation Transformer
(1) The two-wire control circuit shall be obtained from the secondary side of an isolation transformer. One wire from the secondary of this transformer shall be electrically continuous and shall be bonded to a convenient cold water pipe. All metallic enclosures of control components shall be securely bonded to this ground control circuit wire. The primary side of the isolation transformer will normally be a two-wire source with a potential of 230 V or 208 V or 440 V.
(2) Both sides of the two-wire primary circuit shall be fused. The hot leg on the load side of the isolation transformer shall be fused as small as practicable and in no case fused above the rating of the isolation transformer.
HG-633 LIMIT CONTROLS
Limit controls shall be wired on the hot or line side of the control circuit.
HG-634 SHUTDOWN SWITCHES AND CIRCUIT BREAKERS
A manually operated remote heating plant shutdown switch or circuit breaker should be located just outside the boiler room door and marked for easy identification. Consideration should also be given to the type and location of the switch to safeguard against tampering. If the boiler room door is on the building exterior the switch should be located just inside the door. If there is more than one door to the boiler room, there should be a switch located at each door.
(a) For atmospheric-gas burners, and oil burners where a fan is on a common shaft with the oil pump, the complete burner and controls should be shut off.
(b) For power burners with detached auxiliaries, only the fuel input supply to the firebox need be shut off.
HG-640 CONTROLS AND HEAT GENERATING APPARATUS
(a) Oil and gas-fired and electrically heated boilers should be equipped with suitable primary (flame safeguard) safety controls, safety limit switches, and burners or electric elements as required by a nationally recognized standard.
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(b)
The symbol of the certifying organization
3 that has investigated such equipment as having complied with a nationally recognized standard shall be affixed to the equipment and shall be considered as evidence that the unit was manufactured in accordance with that standard.
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ARTICLE 7
INSTALLATION REQUIREMENTS
HG-700 INSTALLATION REQUIREMENTS, ALL BOILERS
HG-701 MOUNTING SAFETY AND SAFETY RELIEF VALVES
HG-701.1 Permissible Mounting. Safety valves and safety relief valves shall be located in the top or side
1 of the boiler. They shall be connected directly to a tapped or flanged opening in the boiler, to a fitting connected to the boiler by a short nipple, to a Y-base, or to a valveless header connecting steam or water outlets on the same boiler. Coil or header type boilers shall have the safety valve or safety relief valve located on the steam or hot water outlet end. Safety valves and safety relief valves shall be installed with their spindles vertical. The opening or connection between the boiler and any safety valve or safety relief valve shall have at least the area of the valve inlet.
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HG-701.2 Requirements for Common Connections for Two or More Valves
(a) When a boiler is fitted with two or more safety valves on one connection, this connection shall have a cross-sectional area not less than the combined areas of inlet connections of all the safety valves with which it connects.
(b) When a Y-base is used, the inlet area shall be not less than the combined outlet areas. When the size of the boiler requires a safety valve or safety relief valve larger than 4½ in. (115 mm) in diameter, two or more valves having the required combined capacity shall be used. When two or more valves are used on a boiler, they may be single, directly attached, or mounted on a Y-base.
HG-701.3 Threaded Connections. A threaded connection may be used for attaching a valve.
