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NORA Oilheat Technicians Manual

speed. Starting windings will draw high current (amps) during the starting phase for a split phase motor. Run windings: Electric current flow in these windings creates the rotating magnetic field in the stator. This maintains the shaft rotation after the start windings have been disconnected. The starting and running windings are oriented perpendicularly to each other. The windings are designed so that the current in one lags the current in the other. The difference makes the resulting magnetic field rotate, creating a torque that turns the motor shaft. Start switch: Start windings draw many amps. On split-phase motors, we turn off the power to these windings once the motor has started to turn in order to conserve electricity. The centrifugally operated switch used in split phase and capacitor start motors opens and disconnects the start winding after the motor reaches 75% to 80% of full speed. The power remains connected to the run windings. The centrifugal switch throw-out speed for a 3,450 RPM burner motor is about 2,800 RPM. The flange end of the motor is sized to bolt onto the oilburner casting. Although most burner manufacturers use the same size flange mount, you may encounter some that are different. Generally, the 3,450 rpm flame retention burner motor has a smaller M flange with a circumference of 6¾". The N flange that can be found on older burners and small commercial motors measures 7¼". Motors are typically rated by voltage, amp draw, direction of rotation, frame size, and horsepower. The motor rating plate provides this information. The frame sizes Chapter 10 Motors 10-4 Motors are established by NEMA (National Electrical Manufacturers Association). Some motors have cooling holes in the motor ends called bells, but some bells are totally closed. The end of the motor around the shaft is the shaft bell and the other end is known as the end bell. The type of shaft bell can affect air pressure and flow for a burner. Shaft bells with fewer air holes will generally provide higher pressure. A reduction in pressure and flow can negatively impact burner operating characteristics. Not all manufacturers refer to rotation in the same manner. Some manufacturers consider rotation when looking at the shaft bell, others by looking from the end bell towards the shaft. Be aware of this when ordering a new motor or when installing a replacement motor that needs to be wired to establish rotation. Motor oiling There are two ways motors are lubricated: 1. Permanently lubricated—this type of motor does not have any oiling ports and should not be oiled. 2. Motors that require lubrication are oiled according to their duty cycle using SAE 20 oil. Occasional Duty— less than 2 hours a day: Oil every 5 years. Intermittent Duty—run 2 to 12 hours a day: Oil every 2 years. Continuous Duty—12 or more hours a day: Oil once every year. Most oilburner motors see intermittent duty. Motors are typically rated by voltage, amp draw, direction of rotation, frame size, and horsepower.


NORA Oilheat Technicians Manual
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