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NORA Oilheat Technicians Manual

Starting Switch (Centrifugal) 10-6 Motors much greater starting torque). Figure 10-4 shows the internal connections of a split phase motor with a start switch and also a start capacitor in the line to the start winding. Many circulator and commercial oilburner motors are capacitor start motors. Thermal or motor overload switch The thermal or overload switch is wired in series with the motor windings and is activated (opens) when an unusual increase in temperature occurs inside the motor. This switch protects the motor from being damaged by overheating. If the motor overheats, the bimetal in the switch will warp then the switch will open and turn off the motor. There are two types used in oilburner motors: 1. Manual reset thermal protectors are most common and must be reset by pressing a reset button. Figure 10-5 shows the operation of a manual reset overload. 2. Automatic reset; this type will reset itself (close) after the motor cools down. Figure 10-6 shows the action of an automatic reset overload. In Figure 10-7, a schematic wiring diagram shows the location of the overload switch in the circuit. When the thermal overload switch shuts the motor off, it indicates motor overheating. This is caused from either internal failure or external loading conditions. The following will cause motor overload: 1. The line voltage is too high or too low. Figure 10-4: Capacitor start split phase motor Figure 10-5: Manual reset overload switch Figure 10-6: Automatic reset overload switch Overload Switch Capacitor 120 Volts AC Line Starting Winding Running Winding Reset Button Spring Bi-Metallic Strip Heater Strip Heater Strip (Bent) Trigger Released Motor Circuit Heater Strip (Cool) Switch Bi-Metallic Disk Heater Strip (Heated) Chapter 10 Motors


NORA Oilheat Technicians Manual
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