Frequently Asked Questions

What are the components of an electric motor?

Understanding the components of a motor and how it works can show how energy wastage can occur within a business. The diagram (below) shows the various parts that make up an induction motor, from the conduit box, where the electrical input is applied (either directly from the mains/grid supply or from a VSD), to the output shaft. Simply put, as electrical power is applied, a rotating magnetic field is created around the stator (1). This induces currents and associated magnetic fields in the rotor (2), causing the rotor and shaft (3) to spin. The shaft is mounted on bearings (4) and is able to rotate freely. When a motor is connected directly to an electrical supply it will accelerate to a fixed speed. However, when starting, the motor will draw a very high current as it accelerates. This is called the ‘motor starting current’. The starting current generates significant heat and it is for this reason that motor manufacturers normally state a maximum number of ‘starts’ per hour, as excess heat will considerably increase motor wear and reduce life expectancy. When a motor is connected to a soft starter or to a VSD, this starting current can be limited and a much smoother start can be achieved, resulting in less wear on the motor.

Why is the term Drive used in relation to electric motors?

The term drive is used to mean many things in industry, including being used as a generic word for motors, for drivetrains (such as gearboxes or pulley systems), and for controllers. More accurately, and for the purposes of this guide, ‘drive’ refers to a motor controller. A variable speed drive (VSD) is an electronic device that controls the electrical supply to a motor, enabling it to run at different speeds

General

  • Question: My motor is very hot to the touch. Is that normal?
  • Answer: Yes, the normal surface temperature for a motor is approximately 100° F. Many motors are also equipped with Thermal Protection. However periodically you should inspect the motor for distortion or bowing of the nameplate, as this would indicate excessive heat.
  • Question: What type of motor must be located in the air stream to be cooled because it is not self-cooling?
  • Answer: Air-over motor
  • Question: Overheating is a sign of inefficiency and/or insufficient ventilation True/False?
  • Answer: True
  • Question: In order to provide the necessary cooling for an “air over” type motor, the motor must be located in an air stream True/False?
  • Answer: True

Motor Temperature/Cooling

  • Question: My motor is very hot to the touch. Is that normal?
  • Answer: Yes, the normal surface temperature for a motor is approximately 100° F.  Many motors are also equipped with Thermal Protection .  However periodically you should inspect the motor for distortion or bowing of the nameplate, as this would indicate excessive heat.
  • Question: What type of motor must be located in the air stream to be cooled because it is not self-cooling?
  • Answer: Air-over motor
  • Question: Overheating is a sign of inefficiency and/or insufficient ventilation True/False?
  • Answer: True
  • Question: In order to provide the necessary cooling for an “air over” type motor, the motor must be located in an air stream True/False?
  • Answer: True
  • Rotation: Motors (for Blower Wheel rotation SEE BELOW)
  • Question: When choosing a motor, how do I know I am getting the correct rotation?
  • Answer: Rotation is obviously an extremely important motor attribute.  While many motors are easily reversible (for example, most three phase motors), others are not.  For non-reversible motors, you must be very careful to check, and double check that the correct rotation is being specified.   Unfortunately, the vendors don’t make it easy on any of us, since the specifications of “CW”, and “CCW” of course depend on the direction you are viewing the motor; i.e. are you viewing the motor by looking at the shaft end or the opposite end.  Some vendors use the shaft end as the reference others use the opposite end.The following table, lists some common rotation specifications which do not depend on the viewing reference.
Label
Description
CCW / LE or CCWLE Counter clockwise from the lead end
CCWSE Counter clockwise from the shaft end
CW Rotation Only Shaft can only rotate in a clockwise position
CW / OLE Clockwise opposite lead end
CWLE Clockwise from the lead end
CWSE Clockwise from the shaft end
Double Shaft / CCWLE Spins counter clockwise on a double shaft from the lead end
Double Shaft / CWSE Spins clockwise on a double shaft from the shaft end
CW / CCW or Reversible Clockwise or counterclockwise
ECW Either clockwise or counterclockwise, connected for clockwise rotation at factory
ECCW Either clockwise or counterclockwise, connected for counterclockwise rotation at factory
Reversing Plug Switching the reversing plug changes the rotation of the shaft
CW or CCW The real meaning of these labels is dependent on the manufacturer. (See illustration below)

View the motor facing the shaft end to determine rotation.

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Counter-Clockwise Rotation (CCW)

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Clockwise Rotation (CW)

  • Question: When you call what view point should you use to give shaft direction of rotation?
  • Answer: Looking at the shaft.

Rotation: Blower Wheels

Blower rotation is often marked on the blower wheel itself. If not, the cups of the blower fins push the air, and that is the direction of rotation. Dust build-up on a blower wheel can help determine the motor rotation. The majority of the dust will be on the leading edge of the fins.

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  • Question: I have a 3 phase motor. How do I change the rotation?
  • Answer: Changing two of the three leads will change your rotation.
  • Question: There is no way to visually determine the direction of rotation of a Shaded-Pole motor True/False?
  • Answer: False
  • Question: Dust build-up on a fan blade, blower wheel or rotor fin can help determine motor rotation True/False?
  • Answer: True

Bearings/Lubrication

  • Question: How often should I lubricate my furnace motor, and what type of oil should I use?
  • Answer: For routine maintenance and for improved bearing life a few drops of 20w non-detergent oil can be applied every 12 months.
  • Question: Ball bearings, under normal operating conditions, will last as long or longer than sleeve bearings True/False?
  • Answer: False
  • Question: Bearing temperatures are a major factor in determining the useful life of a motor True/False?
  • Answer: True

Capacitors

  • Question: Which capacitor lead can be insulated and not used if only one capacitor lead is used in the application wiring?
  • Answer: The brown lead with a white stripe down the side
  • Question: A motor with a shorted capacitor can still start and run, but will operate as if seriously overloaded True/False?
  • Answer: True
  • Question: Capacitors for PSC (Permanent Split Capacitor) motors are only used for starting the motor True/False?
  • Answer: False
  • Question: Run capacitors are oval shaped with single MFD (Microfared) ratings True/False?
  • Answer: True
  • Question: You can always replace a PSC motor with a Shaded Pole motor True/False?
  • Answer: False
  • Question: It is possible for a Permanent Split Capacitor (PSC) motor to operate even if the capacitor is shorted True/False?
  • Answer: True
  • Question: When replacing a motor run capacitor, it is acceptable to use a capacitor rated at a lower voltage True/False?
  • Answer: False
  • Question: Capacitor life is about how many hours?
  • Answer: 60,000 hours.

HP/RPM

  • Question: Using an oversized motor horsepower rating for a replacement will not cause excessive heat in the motor True/False?
  • Answer: False
  • Question: Motors with horsepower ratings below one horsepower are called fractional horsepower motors True/False?
  • Answer: True
  • Question: The RPM of a motor driving a fan blade will increase when the air flow system or filters become clogged True/False?
  • Answer: False

Installation

  • Question: When installing a motor, it is best, when possible, to have the lead exit of the motor at the _____ position.
  • Answer: 6 o’clock
  • Question: It is okay to by-pass thermal protectors to eliminate nuisance tripping True/False?
  • Answer: False
  • Question: On multi-speed motors, you do not always have to connect the common (white) lead to the power line first True/False?
  • Answer: False

Laws and Principles

  • Question: Ohms Law is the basic relationship between voltage, current and resistance in electrical designs. What is the formula?
  • Answer: R=E/I
  • Question: Motors run on the basic principal of
  • Answer: Electromagnetism

Service Factor

  • Question: What is a Service Factor?
  • Answer:A Service Factor is a Measure of the overload capacity designed into a motor. For example: A 1.15 Service Factor means the motor can deliver 15% more then the rated horsepower without injurious over-heating. A 1.0 Service Factor Motor should not be overloaded beyond it’s rated horsepower. Service Factors will vary with different horsepower motors and motor speeds.
  • Question: Don’t replace a general purpose motor (with a service factor), with a special purpose motor that does not have a service factor True/False?
  • Answer: True

Motor Types

  • Question: A clogged furnace filter will decrease the system static pressure True/False?
  • Answer: False
  • Question: Air moving application motors have HIGH starting torque True/False?
  • Answer: False
  • Question: Shaded Pole motors are the least costly and the least efficient of all motors True/False?
  • Answer: True
  • Question: The two most important factors limiting motor life are:
  • Answer: Heat and moisture
  • Question: Multi-speed motors only indicate speed variation when loaded. When they are run without loads, all speeds will be the same True/False?
  • Answer: True
  • Question: Is Repulsion Induction 1 of the 5 basic types of electric motors True/False?
  • Answer: False
  • Question: Which of the these are parts of a basic electric motor?a). Rotor b). Windings c). Starter d). All of them
  • Answer: d. All of them
  • Question: What is the only thing that cannot be determined from a motor with no nameplate?
  • Answer: Voltage
  • Question: Which of these motors is the most Energy Efficient?a). Shaded Pole b). Three Phase c). Split Phase d). Capacitor Start
  • Answer: b. Three Phase

Mounting

  • Question: What’s the difference between F0, F1 and F2 Mounting?
  • Answer: The F mounting refers to the location of the conduit box. See illustration below.
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