THEORY OF OPERATION

JSIIDS operates on the basic theory of a 20-volt dc circuit that has less than 2,000 ohms of resistance being supplied to the detector or detector processors. This voltage is provided from the control unit. A rise in ohmic value of the circuit to 100,000 ohms will trigger an alarm or tamper condition in the control unit.

If you think about that for just a minute, isn't that the way our supervised fire alarm circuit operates? Sure it is! One main point to remember in any alarm system is that a small change in current flow (less than one-tenth of an ampere) can be used to activate an alarm. Our basic Ohm's law provides that a rise in resistance causes a drop in amperage in the same circuit.

When the control cabinet receives an alarm or tamper signal, it then transmits the signal over telephone lines to the monitor cabinet.

INSTALLATION

The installation of components of the JSIIDS must comply with the current edition of the National Electrical CodeR (NFPA No. 70) and with the following requirements for component mounting, conduit, and conductors.

Component Mounting

Wall-mounted components are designed to be held by fasteners that are accessible only through the open door or cover of the component. Before components are mounted, conduit holes should be cut in the enclosure if they are not already provided. All holes should be made with a halfinch chassis punch.

CAUTION

NEVER use a hole saw, since it produces metal shavings that can harm the performance of the equipment.

Conduit

All conductors except phone lines outside the protected area are to be installed in rigid galvanized steel conduit or intermediate metal conduit in accordance with article 345 of the NECR. Conduit outlet boxes, pull boxes, junction boxes, conduit fittings, and similar enclosures are to be cast metal or malleable metal with threaded hubs or bodies. Conduit for JSIIDS circuits are NOT to contain any building wiring.

Conduit is required to be at least one-half inch in size. All requirements for tapered threads, supports, bends, locknuts, and bushings are the same as discussed under hazardous wiring.

Covers on pull and junction boxes used in the installation of the system have to have a tamper switch installed, or be tack-welded, brazed, filled with epoxy, or provided with twist-off screws.

Interior Conductors

Power conductors for 120-volt ac power to control units and monitor cabinets are to be solid copper, no smaller than No. 14 AWG, type RW or RH-RW or THW insulation.

Low-voltage conductors are to be no smaller than No. 22 AWG. They are to be installed using crimp-on spade terminal lugs at all wire connections to threaded screws on component terminal boards.

All neutral conductors and noncurrentcarrying metal parts of equipment have to be grounded.

A wiring diagram of the installed system will be drawn up for each protected area. The diagram should indicate which sensors are installed and show color-coded interconnections between each sensor and the control unit. The diagram will aid in maintenance and troubleshooting. The diagram should be classified confidential and placed in an appropriate security container.

Connections

All requirements for installation and component connections for the JSIIDS will be found in the manufacturers' literature. Foldouts are provided, showing block diagrams that include each component used by the JSIIDS. One point you should remember is that JSIIDS components are manufactured by several manufacturers using government specifications. Always check the terminal boards before connecting your conductors. Although one system may have terminals numbered from left to right, the terminals on the next system you install may be numbered from right to left. Always check before you connect.