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6. Nuts at the end of the sensing elements [Figure 9-15] should be inspected for tightness and the presence of a safety wire. Loose nuts should be retorqued to the value specified by the manufacturer’s instructions. Some types of sensing element connection joints require the use of copper crush gaskets, which should be replaced any time a connection is separated. 

7. If shielded flexible leads are used, they should be inspected for fraying of the outer braid. The braided sheath is composed of many fine metal strands woven into a protective covering surrounding the inner insulated wire. Continuous bending of the cable or rough treatment can break these fine wires, especially those near the connectors. 

8. Sensing element routing and clamping should be inspected carefully. [Figure 9-14]  Long, unsupported sections may permit excessive vibration that can cause breakage. The distance between clamps on straight runs, usually about 8–10 inches, is specified by the manufacturer. At end connectors, the first support clamp is usually located about four to six inches from the end connector fittings. In most cases, a straight run of one inch is maintained from all connectors before a 

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bend is started, and an optimum bend radius of three inches is normally applied. 

9. Interference between a cowl brace and a sensing element can cause rubbing. [Figure 9-16]  This interference may cause wear and short the sensing element. 

10. Grommets should be installed on the sensing element so that both ends are centered on its clamp. The split end of the grommet should face the outside of the nearest bend. Clamps and grommets should fit the element snugly. [Figure 9-17] 

## Fire Detection System Troubleshooting 

The following troubleshooting procedures represent the most common difficulties encountered in engine fire detection systems: 

1. Intermittent alarms are most often caused by an intermittent short in the detector system wiring. Such shorts may be caused by a loose wire that occasionally touches a nearby terminal, a frayed wire brushing against a structure, or a sensing element rubbing against a structural member long enough to wear through the insulation. Intermittent faults often can be located by moving wires to re-create the short. 

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