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NORA Oilheat Technicians Manual

Chapter 10—Motors 10-7 2. The oil pump has seized due to rust or debris in the gear set. 3. The motor bearings are bad. 4. The return is plugged. 5. There is misalignment of motor to pump—check to see if any mounting bolts have loosened, causing improper seating of the motor or pump to the burner housing. Also, check to see if the pump coupling is too long, causing pressure on the motor shaft. 6. The start switch is dirty or broken. This prevents electricity from flowing to the starting windings. With this switch open, current will still flow to the run winding, but the motor will not start. The increased amperage will generate heat in the line and cause the overload switch to trip out. 7. The centrifugal start switch has failed to disconnect the start windings from the AC power when the motor has reached approximately full speed; the motor will overheat. 8. The fan or blower wheel is jammed or very dirty. Figure 10-8: Ammeter Figure 10-7: Overload switch location Overload Device To Line 9. The motor is in a very hot environment (the inside of a hot vestibule of a furnace). 10. There is dirt in the motor cooling vents; this will also cause the motor to overheat. 11. The motor is undersized— if the load requirement exceeds the nameplate rating for horsepower (HP), the motor will eventually overheat. Use a clamp around ammeter (Figure 10-8) to make sure the motor current does not exceed 10% over the motor nameplate current. Wiring connections and reversing rotation Some oilburner motors have an “S” cord attached to the motor and connected to a junction box. If this is the case, be certain the BX cable or conduit to the junction box is tightly fastened to provide a good bonding to ground. If Romex cable is used, be certain the bonding wire is fastened to the junction box. The motor rotation on some oilburner and blower motors can be electrically reversed. The instructions may be found on the nameplate of the motor or inside the cover that provides access to the wiring connections. The rotation of a motor is determined by the direction of the current to the start winding. If we reverse the connections to the start winding we can reverse the rotation of the motor. The instructions with each motor will identify these connections and how to change them. Figure 10-9 shows how to switch the wires to reverse rotation. Chapter 10 Motors


NORA Oilheat Technicians Manual
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