Question 1

Belt tension will not have any affect on the wear of the bearings.

Accepted Answer

Belt tension plays a crucial role in the wear and tear of bearings. Over-tensioned belts exert excessive pressure on bearings, leading to their premature failure. On the other hand, under-tensioned belts cause bearings to loosen up and cause misalignment, leading to wear and damage over time. Therefore, it is essential to maintain the correct belt tension to ensure the optimal performance and longevity of the bearings.

Question 2

A technician needs to check a single-phase compressor. He labels the three terminals "A," "B," and "C" and takes resistance readings of the windings. He reads 10 ohms from "A" to "B," infinity from "B" to "C," and infinity from "C" to "A." Identify the terminals.

Accepted Answer

The readings of infinity from "B" to "C" and from "C" to "A" indicate an open winding, as there should be some resistance value between all terminals in a functioning compressor.

Question 3

If a resilient-mounted motor develops a short to the frame, the technician can simply cut the ground strap wire as a permanent repair.

Accepted Answer

Cutting the ground strap wire as a permanent repair is not a safe or effective solution. A short to the frame can cause electric shock, fire, or damage to the motor. The technician should diagnose the cause of the short and repair or replace any faulty components.

Question 4

If the cost of repairing the motor is close to the cost of replacing the motor, it would definitely pay to repair the motor if the new component carries a one-year warranty and the repaired motor carries only a 90-day guarantee.

Accepted Answer

It would not pay to repair the motor in this scenario since the new component carries a longer warranty than the repaired motor.

Question 5

The recommended way to discharge a capacitor is to ____.

Accepted Answer

Using a 20,000 ohm 5 watt resistor that has had insulated leads soldered to it is the recommended way to discharge a capacitor. This is a safe and effective method that prevents damage to the capacitor and ensures the safety of the technician. Placing a screwdriver across the terminals or using an ohmmeter can be dangerous and may cause injury or damage to equipment. Assuming the capacitor will discharge itself over time is also not a reliable method and could take a significant amount of time.

Question 6

Open winding will not affect the resistance reading of the start winding as well as the resistance reading between the Run and Start terminals.

Accepted Answer

An open winding will cause the resistance reading between the Run and Start terminals to be infinite, indicating an open circuit. The resistance reading of the start winding may also be affected, depending on the location of the open circuit.

Question 7

If a motor hums but does not start, there is a potential problem ____.

Accepted Answer

A motor that hums but does not start could indicate a problem with the starting components such as the capacitor or centrifugal switch, an open winding, or insufficient supply voltage. Therefore, all of the above options could be potential problems.

Question 8

If the resistance of the run winding is lowered, the imbalance in magnetic fields between the start and the run winding will be increased, and the starting torque of the motor will actually increase.

Accepted Answer

When the resistance of the run winding is lowered, the current flowing through it will increase. This will cause the magnetic field produced by the run winding to become stronger and thus increase the imbalance in magnetic fields between the start and run windings. As a result, the starting torque of the motor will increase.

Question 9

What is the best method to repair a fractional horsepower motor that has bad bearings?

Accepted Answer

The answer of What is the best method to repair...

Question 10

Most electrical problems with an electric motor are ____.

Accepted Answer

Short circuited windings, open windings, and grounded windings are the most common electrical problems with an electric motor. Short circuited windings occur when the insulation between the individual coils of wire breaks and the coils touch each other. Open windings occur when a coil of wire breaks or becomes disconnected. Grounded windings occur when one of the coils of wire touches the metal frame of the motor.

Question 11

The electrical components for a fully welded hermetic compressor are checked at the disconnect box for the compressor unit.

Accepted Answer

The electrical components for a fully welded hermetic compressor are sealed inside the compressor shell and cannot be accessed or checked at a disconnect box. The disconnect box is used for cutting off power, not for checking internal components of a hermetic compressor.

Question 12

Pulleys must be in proper alignment or belt and bearing wear will occur.

Accepted Answer

Pulleys must be aligned properly to ensure that the belt runs smoothly and the bearings are not subjected to unnecessary wear and tear. If the pulleys are misaligned, it can cause the belt to slip, which leads to increased friction, heat, and wear on the belt and bearings. Therefore, it is essential to maintain proper alignment of pulleys to ensure optimal performance and longevity of the equipment.

Question 13

If a condenser fan motor grounds out, it will usually ____.

Accepted Answer

When a condenser fan motor grounds out, it can cause a short circuit and trip a circuit breaker to shut off the unit as a safety measure. If the fan motor keeps running as the current is only going to ground, it can cause overheating and damage to the motor. Running a little faster because the amperage draw will increase is not a likely scenario. The evaporator does not have a direct connection to the condenser fan motor, so it cannot be affected by a grounding issue in the fan motor.

Question 14

If the resistance of the run winding decreases, the ____.

Accepted Answer

If the resistance of the run winding decreases, the motor will draw too much current while it is running. As the current increases, it can damage the motor and also place a strain on the electrical system powering it. This increased current draw is due to the fact that if the winding resistance decreases, there is less opposition to electrical current flow.

Question 15

The wiring and connectors that carry the power to a motor must be in good condition. When a connection becomes loose, oxidation of the copper wire occurs. The oxidation ____.

Accepted Answer

Oxidation of copper wire acts as an electrical resistance and causes the connection to heat more.

Question 16

Before testing a run or start capacitor with an ohmmeter, the capacitor should be discharged with a 20,000-ohm 5-watt resistor.

Accepted Answer

This is correct. Before testing a capacitor with an ohmmeter, it should be discharged to prevent any electric shock. A 20,000-ohm 5-watt resistor can be used to discharge a capacitor.

Question 17

An open winding in an electric motor means that ____.

Accepted Answer

An open winding in an electric motor means that a wire in a winding is broken, causing a break in the circuit and preventing the motor from functioning properly.

Question 18

Technician "A" says that a shorted winding will result in an increased current flow through the winding. Technician "B" says that if a motor is to be replaced, a motor with a lower horsepower rating should always be used. Which of the following statements is correct?

Accepted Answer

A shorted winding will decrease the resistance of the winding, resulting in an increase in current flow. Technician "A" is correct. However, it is not always appropriate to use a motor with a lower horsepower rating to replace a motor. The replacement motor must have at least the same horsepower rating as the original motor or a higher rating, depending on the specific application. Technician "B" is incorrect.

Question 19

A megger ____.

Accepted Answer

A megger is an instrument used to measure high electrical resistances, typically above 1 megaohm. It works by applying a high voltage DC test signal to the component or material being tested, and measuring the resulting current flow. This allows for the detection of insulation faults and other issues in cables, wires, transformers, and other electrical devices.

Question 20

Technician "A" says that while checking the windings of a compressor, a reading of 10 ohms or less from the common terminal to ground indicates that the motor is okay. Technician "B" says that the resistance of the start winding should always be less than the resistance of the run winding. Which of the following statements is correct?

Accepted Answer

Technician "A" is incorrect because a reading of 10 ohms or less from the common terminal to ground typically indicates a short to ground, not a healthy motor. Technician "B" is incorrect because the resistance of the start winding is usually higher than the resistance of the run winding, not less.

Quiz 20: Troubleshooting Electric Motors