OM2025.1 Safety - Section 2 General Safety Page 2-19 Engine Shutdown Procedure before Welding or Performing Maintenance Normal operation of the drive system at shutdown should leave the system safe to maintain. However, in the event of a system failure, performing the following procedure prior to any maintenance activities will ensure that no hazardous voltages are present in the AC Drive System. 1. Before shutting down the engine, verify the status of all the drive system warning lights on the overhead display panel (Figure 3-7, Section 3 - Operation). Use the Lamp Test Switch (8, Figure 3-7, Section 3 - Operation) to verify that all lamps are functioning properly.
If any of the RED Drive System warning lights remain ON, do not attempt to open any cabinets, disconnect any cables, or reach inside the retarder grid cabinet without a trained drive system technician present - even if engine is shut down. Only qualified personnel, specifically trained for servicing the AC Drive System, should perform this service. 2. If all red drive system warning lights are off, follow the “Normal Engine Shutdown Procedure”. 3. After the engine has been stopped for at least five (5) minutes, inspect the LINK VOLTAGE lights on the exterior of the main control cabinet and back wall of the operator’s cab (DID panel).
If all lights are OFF, the retard grids, wheel motors, alternator, and power cables connecting these devices are safe to work on. 4. Locate the “GF” Cut-out switch in the access panel on the left side of the main control cabinet. Place the switch in the “Alternator Cutout” position. This will prevent the alternator from re-energizing and creating system voltage, until the switch is returned to its former position. 5. The blower motors, control cabinet and power cables connecting these devices are still unsafe. To establish that these devices are safe, open the top control cabinet cover and inspect the red lights on the blower control panel.
If these lights are OFF, the blower system, blower power cables and remainer of the control cabinet is safe to work on. If these lights are ON, refer to steps 11 – 12. 6. Before welding on the truck, disconnect all electrical harnesses from the Engine Control System (ECS) inside the electrical cabinet behind the operator’s cab. Also, disconnect the ground strap from the ECS. 7. Do not weld on the rear of the control cabinet! The metal panels on the back of the cabinet are part of capacitors and cannot be heated. 8. Do not weld on the retard grid exhaust louvers - they are made of stainless steel. Some power cable panels throughout the truck are also made of aluminum, or stainless steel.
They must be repaired with the same material, or the power cables may be damaged. 9. Power cables must be cleated in wood or other non-ferrous materials. Do not repair cable cleats by encircling the power cables with metal clamps or hardware. Always inspect power cable insulation prior to servicing the cables and prior to returning the truck to service. Discard cables with broken insulation. 10. Power cables and wiring harnesses should be protected from weld spatter and heat. Always fasten the welding machine ground (-) lead to the piece being welded; the grounding clamp MUST BE ATTACHED AS NEAR AS POSSIBLE to the weld area .
Always avoid laying welding cables over or near the vehicle electrical harnesses. Welding voltage could be induced into the electrical harness and possibly cause damage to components. Before doing any welding on the truck, always disconnect the battery charging alternator lead wire and isolate electronic control components before making welding repairs. In addition, always disconnect the positive and negative battery cables of the vehicle. Failure to do so may seriously damage the battery and electrical equipment. Never allow welding current to pass through ball bearings, roller bearings, suspensions, or hydraulic cylinders.