SM-6495 - Ansaldo STS

General Maintenance and Troubleshooting3. GENERAL MAINTENANCE AND TROUBLESHOOTINGWARNINGTo avoid bodily injury when performing any maintenance on the Model95 Gate Mechanism, the following steps MUST be taken:Position the gate arm of the Mechanism being serviced in the desired position (SeeSection 3.2.9),Electrically disconnect the Mechanism being serviced by loosening the gold nut onTerminal 5B, andRemove and insulate the B12 (or B24) supply wire from Terminal 2C.3.1. Safety Considerations at Multiple Gate LocationsWhen performing maintenance on a Model 95 Gate Mechanism with the gold nut (5B) open (Figure3-2) and pinning the gate in the UP position, it is possible to back-feed an adjacent Model 95Mechanism with enough energy to prevent its Hold Clear (brake) coil from de-energizing when thecrossing is activated. As a consequence, the gate arm of the adjacent mechanism may not descendwhen required. This is only possible if multiple Gate Mechanisms at a given location share a commonUP Control input. This is not a problem if each mechanism has its UP Control input derived viaseparate contacts of the Crossing Control Relay (XR or XPR).Therefore, the best practice is to provide the UP Control input to each mechanism at a multiple-gatelocation through a separate contact of the Crossing Control Relay (XR or XPR). If a solid-statecontroller provides the Crossing Control output, this output should drive the XR, instead of using it tocontrol multiple mechanisms through diode-OR’d circuits.If the above recommended best practice is not feasible for whatever reason, one of the followingactions, in addition to opening the gold nut (5B), shall be taken for the gate that is being taken out ofservice and locked in the up position:1. Place insulation between the power down contact 3A-3C (Figure 2-2, Figure 2-3, Figure 2-4, orFigure 2-5), or2. Disconnect the Gate Control (GC) wire at terminal 1C.SM 6495, Rev. 7, December 2008 3-1