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1.0 INTRINSIC SAFETY General-purpose external horn relays, horns and bells can be used if wiring is isolated, provided they all use Hazardous atmospheric mixtures include all the power from the intrinsically safe power supply. explosive or ignitable air mixtures involving gases or If the power to the horns is to be supplied from a vapors at an atmospheric pressure and with ambient source other than the intrinsically safe power supply, temperatures between zero and 120°F. The order of isolation of the other voltage source must be main- ignitability of materials generally corresponds to the tained by using the Model KV-700 or X53-1014 Horn National Electrical Code groupings. The workable Relay or any other approved horn relay. categories and test materials used as typical for each are: To be completely assured of an intrinsically safe installation, all equipment used must be approved by Group A: acetylene (8.7% by volume) an agency, and the installation, including the wiring, Group B: hydrogen (21.0% by volume) plus all the contact inputs, must meet requirements of Group C: ethylene (7.8% by volume) isolation to avoid any failures that may occur in the Group D: methane (8.2% by volume) system. The ignition capability of an electrical circuit is CAUTION: The X76S Monitor enclosure may be determined by the electrical energy available and the mounted in a Class I, Division 2, Groups C, D manner in which such energy is released. Energy may hazardous area as defined by the National Electrical be released in the form of a spark, by resistive heating Code. effects or a combination of the two. There are three basic mechanisms by which electrical energy may be Power input maximum is 115 VAC, 60 Hz. released in the form of spark discharge: discharge of All wiring to sensors (i.e. Level Switches LS-3, LS-7, a capacitive circuit, interruption of current in an LS-10, LS-20, LS-30 and Pressure Switches JT-2P and r inductive circuit and make-break of a resistive circuit. JT-2V), must be installed in separate dedicated The minimum ignition energy for any flammable conduit to comply with the intrinsically safe mixture is the smallest amount of energy released as requirements. a spark and sufficient to ignite the mixture at 0 psig. All wiring to auxiliary relays KV-700 and X53-1014 The most easily ignited air mixture is that mixture of a must comply with drawings. flammable material in air, which requires the minimum All external equipment used with system must amount of energy for ignition. The flammables are comply with National Electrical Code for the area d' usually designated in percent by volume in air where the equipment is being installed. This is Normal operating conditions include maximum supply particularly important when selecting external horns, voltage and the extreme environmental conditions pushbuttons and relays to be used with the X76S which fall within the ratings given for the specific System. equipment under investigation. The X76S chassis must be properly grounded Abnormal operating conditions usually refer to any two including the intrinsically safe ground. mechanical or electrical faults occurring in combin- NOTE: Ronan Engineering Company does not accept ation. The faults are independent and include the responsibility of the installation of intrinsically accidental damage to, and failure of, components or safe equipment. wiring. Intrinsically safe electrical equipment and the associated wiring are incapable of releasing into the air sufficient electrical or thermal energy (under 2.0 SPECIAL CAUTIONARY NOTES- normal or abnormal operating conditions) to ignite a INTRINSICALLY SAFE MONITORS specific hazardous mixture in its most concentrated, f easily ignitable form. The flammable material may be Before applying power and beginning the test a gas or vapor. procedure, it is important to review all the elements of Underwriters Laboratory and Factory Mutual approvals the monitor system, including the cabinet itself, to are based on examination and tests of samples of verify that each component meets the requirements of production-quality equipment and inspection of manu- the National Electrical Code for the area in which it is facturing and quality-control facilities. Of particular installed. Particular attention must be paid to consideration are the adequacy of design and work- reviewing the selection of any externally supplied manship, uniformity and dependability of production, pushbuttons, horn relays, horns and bells, to assure effectiveness of quality control, functional suitability, that they are of an appropriate classification. assurance of availability of service and replacement of . - parts. 2.1 Alarm Contact Inputs Installation of intrinsically safe annunciators makes it Each alarm contact of the intrinsically safe mandatory to maintain complete isolation between the system must be brought to the alarm contact field contact wiring and any other potential source of inputs, labelled "1A" and "113," as the discrete voltage. pair of wires. The common practice of running 2 �