Motor Controls
Student Study Notes 2014
WARNING INSTRUCTOR OR LAB AIDE SUPERVISION IS ABSOLUTELY REQUIRED FOR ALL LAB ACTIVITES SINCE EVEN THE LOW VOLTAGES USED IN MOST OF THESE LABS CAN BE FATAL.
Note, if you have not completed Electrical Troubleshooting you must complete the safety and lock out tag out section. You should read through thestudent study notes up until Motors & Controls (2014 revision).
The motor controls section of the SSNs starts there.
Electrical Safety
1. List at least 10 rules of electrical safety. Decide which two are the most important and why you think these two are so important. (For Mechatronics students, make this list neat and clear since you will be signing it as a contract to work safely in the lab and later, on the job.)
2. How does low amperage kill? (HVAC, 2nd edition; HV p. 64)
3. What safety precautions will you take when you must work on live electrical circuits for troubleshooting?
4. What happens when a person becomes grounded?
5. What is the function of a ground circuit? (IM Fig 4-19; HV p. 64-66)
6. What is the purpose of a ground fault circuit interrupter (CFCI) (HV p. 66) ?
7. What determines the type of electrical personal protective equipment will you use on the job?
8. What national code regulates electrical safety?
9. What type of PPE protects against arc flash injuries?
10. Study Figure 2-21 & 2-22 p. 46 regarding safe approach distances.
Learning Activities: Industrial Maintenance, 3rd edition (IM), ELECTRICAL SAFETY, p. 43 - 48
Lockout/Tagout
1. Why is it difficult to conduct electrical troubleshooting on de-energized electrical circuits?
2. What is the title and purpose of the law that governs lockout and tagout?
3. What must be posted near each complex machine?
4. List the steps for applying and removing a lockout.
5. What must happen at shift change?
6. How do lockout and tag out rules apply to outside workers coming into the facility?
7. State the rules regarding locks used for lockouts.
8. State the rules for tags used for tag outs.
9. List all the types of energy sources that must be locked out.
10. List the three groups of workers and describe their level of involvement with logout and tag out.
11. State the rules regarding inspections of lockout and tag out procedures.
12. How are group lockouts managed?
Learning Activities: (IM), LOCKOUTS AND TAGOUTS, p. 48 - 49
Power Distribution
1. Briefly describe how electricity is distributed from the power generation plant to a load in a commercial facility. (IM, Fig. 4-12)
2. What is the function of a service entrance switchboard?
3. What is the function of a distribution switchboard?
4. What is the function of a circuit breaker panel?
5. How is it decided what type of electrical enclosure to use?
6. Describe the construction of a plugin busway.
7. Where do feeder circuits run?
8. Where do branch circuits run?
9. Define voltage, current, and resistance. (HV p. 340-341)
10. What is the total voltage drop allowed for a circuit?
11. Sketch and label one cycle of a 1Ø sine wave. (IM, Fig. 4-14; HV p. 345-346)
12. What is RMS in relation to the sine wave?
13. Sketch and label one cycle of a 3Ø sine wave.(IM, Fig. 4-15)
14. Sketch and describe the various types of DC voltage. (IM, Fig. 4-16)
15. Sketch the voltage measurements between the wires of a 120 V circuit, a 208 V 1ø circuit, a 208 V 3ø circuit, and a 460 V 3ø circuit. (HV p. 365 -367)
16. Describe a residential120/220 V 1Ø service. (HV p. 365-366)
Learning Activities: IM, POWER DISTRIBUTION p. 120 -124
LAB: Test a 3 phase power supply
If a load like a 3ø motor is not energizing verify that the correct voltage is available. This is called testing source voltage and it is the measuring of a voltage rise. A 3ø power supply consists of three hot wires and a safety ground wire. Connecting the volt meter probes between any two of the three wires should produce a reading of source voltage +/- 5%
208 voltage source readings should be: between line 1 and line 2 = 208, between line 1 and line 3 = 208, and between line 2 and line 3 = 208, between line 1 and ground = 120, between line 2 and ground = 120, between line 3 and ground = 120.
480 voltage source readings should be: between line 1 and line 2 = 480, between line 1 and line 3 = 480, and between line 2 and line 3 = 480, between line 1 and ground = 277, between line 2 and ground = 277, between line 3 and ground = 277.
This test might be conducted at a fused disconnect, at a receptacle plug-in, at the motor leads, or at a 3ø circuit breaker.
LAB: Test a high voltage 1 phase power supply
High voltage single phase motors have two hot wires and a ground wire. Some heating element, welders, and AC units are also high voltage single phase (two phase). Connecting the volt meter probes between any of the two hot wires should produce a reading of source voltage +/- 5%
208 voltage source: between line 1 and line 2 = 208, between line, between line 1 and ground = 120, between line 2 and ground = 120.
480 voltage source readings should be: between line 1 and line 2 = 480, between line 1 and line 2 = 480, between line 1 and ground = 277, between line 2 and ground = 277.
Electric Circuits
1. What is the purpose of any electrical circuit?
2. What happens to the electrons in the wire when a voltage source is applied to the wire? (IM, Fig. 4-1 & 4-2; HV p. 337-338)
3. Are electrons consumed like firewood or gasoline?
4. What are the characteristics of a good insulator, a good conductor, and a
semiconductor? Give an example of each type of material. (HV p. 339)
5. What must every electric circuit contain?
6. Sketch and describe an open circuit and a closed circuit. (IM, Fig. 4-36)
7. Sketch and describe how to test a set of contacts (a switch). (IM, Fig. 4-40)
8. What is the function of a voltmeter, ammeter, and ohmmeter. (HV p. 347-348)
9. Sketch how a voltmeter is connected into a circuit.
10. Why is a voltmeter a high resistance instrument?
11. Sketch and describe a voltage drop and a voltage rise. (IM, Fig. 4-19)
12. What are the uses of a bar graph on a DMM?
13. How are ghost voltages produced?
14. What is a practical application of using ghost voltages when troubleshooting circuits? (IM Fig 4-36)
Check-off Method
As you troubleshoot circuits you will work from a wiring diagram or schematic. To check to see if the circuit is wired correctly, use the check off method. Working from the schematic find and trace each wire. When the wire is checked and verified to be correctly placed and securely connected, check mark the wire on the schematic. Work through the circuit in a logical order and make sure to check every wire. This method works for most electrical and electronics circuits and even hydraulic and pneumatic circuits. Make sure the circuit is de-energized when using the check off method since you are likely to come into contact with potentially live components, or you could pull loose a live wire that might cause a dangerous short circuit.
Learning Activities: Use the Check-off Method on all lab activities.
LAB: Describe how you will find an operational short or a wiring problem.
Use the check-off method when you have a malfunctioning circuit, but the fuse or circuit breaker does not blow. For example, two lights might light when only one should light. Make sure the circuit is completely de-energized. Study the system prints and locate the part of the circuit that is likely to contain the fault then use the check-off method to locate the problem. Look for crossed wires connecting two branches of a circuit, incorrectly installed wiring, or incorrectly numbered wires or swapped wires, 6 for 9 for example.
LAB: Sketch and describe how to locate an open circuit and test contacts using a voltmeter.
The circuit will be de-energized if there is a series open, for example a light switch that turns off all the lights.
If the switch you are testing with your voltmeter and switch is closed you should read nearly .000 volts. This means that no voltage is being used “dropped” as the current flows through the closed contacts. You do not want contacts using voltage or they will heat up and eventually fail. Depending on the sensitivity of the meter you might actually see a very small reading, for example 136 mV instead of .000V. When you read the meter display make sure you read not just the numbers but the units that the numbers represent. The trick is to watch the meter readout since it will change as the contact change position. When switch is open you should read source or ghost voltage, more on ghost voltage later. When the contacts close the meter screen will go blank the read nearly zero volts. Individual lengths of wire can be tested using a voltmeter with the same readings.
If a switch is open and you use a jumper wire to bridge the switch the equipment should start. Use extreme caution since the circuit will energize using this test. If the circuit energizes properly, then the component that is jumpered is defective. Be sure that you do not jumper around a load since this will cause a short circuit. Make sure the jumper is removed after the circuit is repaired. Use jumper wires of an odd colored wire so that you will notice it if it is left on the circuit.
LAB: Sketch and describe how to test contacts using an ohmmeter.
Always remove the component being tested from the circuit to get an accurate measurement and to avoid damaging your meter, or worse. Contacts will read nearly .000 ohms when closed, OL when open. Contacts that do not operate in this fashion are not operating correctly. The trick is to watch the meter readout since it will change as the contacts change position. If the closed contacts offer higher than expected resistance they are dirty or worn and must be replaced, or they are not closing completely and need adjustment.
IM, TESTING FUSES AND CIRCUIT BREAKERS, Fig. 4-36 p. 139
LAB: Sketch and describe how to locate multiple opens in series.
If there are several opens in series a high quality digital meter will register ghost voltage when the probes bridge one of the opens. Ghost voltage is usually a low voltage that has no logical explanation in terms of circuit operation. It results from the increased sensitivity of digital meters which are probably measuring the capacitive energy across the multiple opens.
The voltmeter will register near source voltage when the probes bridge all of the opens.
IM, TESTING CONTACTS, p. 144 Fig. 4-40.
Fuses
1. Sketch and describe the operation of a fuse. (HV p. 362)
2. What is the purpose of a fuse?
3. What type of fuse is used to protect electric motors? How does it operate?
4. Sketch and describe the ohmmeter test of a fuse. (IM, Fig. 4-35)
5. What does an ohmmeter measure? How does one work?
6. Why do you never use an ohmmeter on a live circuit?
7. What are the values of the following symbols: K = kilo = , M = mega = m = mille =
8. Sketch and describe the voltmeter test of a single fuse.
9. What is the purpose of a fused disconnect?
10. How will you test fuses in a three phase fused disconnect? (IM, Fig. 4-35)
11. Why do you not put in a higher rated fuse if a lower rated fuse keeps blowing?
12. What is the purpose of a circuit breaker? (IM, Fig. 4-35; HV p. 363-364)
13. How will you test a circuit breaker? (IM, Fig. 4-35)
14. What maintenance do circuit breakers or any seldom used switches require?
Learning Activities: IM, Over Current Protection Devices p. 136-138, Fig. 4-34 & 4-35
LAB: Test fuses and a circuit breaker using a voltmeter and an ohmmeter.
Single Fuse: An individual (single phase) fuse is tested using the same method as testing a switch or a set of contacts on a relay using a voltmeter. The probes are placed across the fuse, one on each end of the fuse. A good fuse receiving voltage will register near zero volts, a bad fuse will register source voltage or ghost voltage. If a fuse is not receiving voltage it will read 0 volts so you must determine that the correct voltage is being applied to the circuit as part of a fuse test.
If you think the fuse is bad (open), de energize and lock out the circuit then remove the fuse from its holder using a fuse puller, not any other tool! Place the fuse on a non conductive surface like wood and place the probes of the ohmmeter on either side of the fuse. A good fuse will register a very small resistance; a bad fuse will register OL.
Three phase fuses: After ensuring that there is power available to all three phases, fuses in a 3 phase fused disconnect are tested by placing one probe of the voltmeter on the line side (top) of one fuse, and the other on the load side (bottom) of the fuse next to it. The test proceeds as if you were testing a three phase power supply with the following readings.
208 voltage source: between line side fuse 1 and load side fuse 2 = 208, between line side fuse 1 and load side fuse 3 = 208, and between line side fuse 2 and load side fuse 3 = 208.
480 voltage source: between line side fuse 1 and load side fuse 2 = 480, between line side fuse 1 and load side fuse 3 = 480, and between line side fuse 2 and load side fuse 3 = 480.
If you think one of the fuses is bad, remove it from the circuit as described above and test it using an ohm meter.