RQ Chapter 8 - Quiz - commercial ref - 7/16/17

What is a good rhyme to remember the wiring terminals of a potential relay ?

" 5,2,1, Can She Run "

What are the 4 things a technician needs to know when choosing a contactor ?

1. The number of poles 2. The compressor amperage 3. The line voltage of the load 4. The control circuit voltage

What are 3 types of start relays ?

1. current relays 2. potential relays 3. positive temperature co-efficient relays ( PTC )

What are the 3 voltage ratings are on a potential relay ? What do they stand for ?

1. pick-up voltage - the voltage it opens contacts 1 and 2. 2. drop out voltage - the minimum voltage required to keep the contacts open . 3. continuous voltage - the maximum continuous voltage the coil open brackets between contacts 5 and 2 ] can handle.

What are the 2 functions of a start relay ?

1. provide full power to the start winding 2.to open the start winding circuit when the motor is up to speed

What is the nominal rpm of a 2- pole motor ? a. 3,000 , 1,600 , and 1,200 rpm b. 3,600 , 1,800, and 1,200 rpm c. 7,200 , 3,200 , and 1,600 rpm

3,600 , 1,800, and 1,200 rpm

On a single phase motor, if the ohm reading for R-S to 6 ohms and the ohm reading for R - C is 1.5 ohms, what should be the ohm reading for S -C ? a. 4.5 ohms b. 7.5 ohms c. 3 ohms

4.5 ohms

A start cap is added to a start relay for compressors on what type of system - cap tube or TEV systems ? Why ? a. A cap tube system , because it needs pressure to push through the tube. b. A TEV system , because the system does not equalize during the off cycle. c. A TEV system, because the valve opens on start up and pressurizes the system .

A TEV system, because the system does not equalize during the off cycle.

How is a motor starter different from a contactor ? a. A motor starter breaks and makes all 3 circuits. b. A motor starter has overloads. c. A motor starter shuts off the circuit breaker, then resets it.

A motor starter has overloads.

what is the difference between the windings in a 3 phase motor and a single phase motor ? a. A single phase has both start and run windings. b. A three phase motor has only start windings. c. A single phase motor has only run windings.

A single motor has only run windings.

Motor overloads open a circuit in responsive to what ? a. Voltage only, if iit is an external overload. b. Amperage only, if it is an internal overload. c. Heat, amperage, or a combination of the two , depending on the overload.

Heat, amperage , or a combination of the two, depending on the overload.

A single phase motor makes no sound, and does not try to start . What is the first thing to check ? a. If the motor has full voltage to the compressor terminals. b. If the internal overload is open. c. If the motor is mechanically seized.

If the motor has full voltage to the compressor terminals.

If a 3 phase compressor is not even trying to start, what is the first thing to check ? a. If the motor has full voltage to the compressor terminals. b. If the internal overload is open. c. If the motor is mechanically seized.

If the motor has full voltage to the compressor terminals.

How is the start capacitor wired in the electrical circuit ? a. In series with the run winding b. In parallel with the run winding c. In series with the start relay

In series with the start relay

Why do some manufacturers add a resistor to a start cap ? a. It makes the capacitor cheaper to manufacture. b. It bleeds off excess electrical charge when the capacitor is not in the circuit. c. It adds excess electrical charge to the capacitor in order to provide more of a phase shift during start-up.

It bleeds off excess electrical charge when the capacitor is not in the circuit.

Why is resistor removed before using a meter to check the capacitor ? a. It will cause the meter to give an inaccurate reading. b. It will harm the electrical meter. c. It could overheat and cause a fire.

It will cause the meter to give an inaccurate reading.

How is a current relay checked within ohmmeter ? a. L-S contacts should be open , and the relay coil [ L - M ] , should have measurable resistance. b. L- S contacts should be open , and the relay coil [ L - M ] should have no resistance. c. L -S contacts should be closed, in the relay coil [ L - M ] have infinite resistance.

L -S contacts should be open, and the relay coil [ L -M ] should have measurable resistance.

How is a magnetic overload different from a thermo-disc- type external overload ? A Magnetic overloads are not as accurate as thermo-type overloads. b. Magnetic overloads accurately respond only to amperage and are not affected by ambient air temperature. c. Thermal overloads must be used on open motors ; magnetic overloads must be used on compressors.

Magnetic overloads accurately respond only to amperage and are not affected by ambient air temperature.

Are the contacts ( L - S ) of a current relay normally open (NO) or normally closed ( NC ) ? a. NO b. NC

NO

If the ohm reading from T2 to ground ( on the suction line ) is infinite (OL) , is there a problem ? Why ? Why not ? a. Yes, there should be measurable resistance to ground. b. No, there should not be any measurable resistance to ground. c. It depends ; the motor would have to be running to check it.

No, there should not any measurable resistance to ground.

If a 3 phase compressor seems to be mechanically locked up, what is the next step ? a. Quote the customer a new compressor. b. Reverse the motor rotation to see if the compressor will run. c. Rebuild the compressor.

Reverse the motor rotation to see if the compressor will run.

On a 3 phase compressor motor, If the ohm readings for T1 - T2 is 2 ohms, what would be the ohm reading between T2 and T3 , and between T3 and T1 ? a. T2-T3 = 6 , T3 - T1 = 8 b. T2 - T3 = 8 , T3 -T1 = 6 c. T2 -T3 = 2 , T3 - T1 = 2

T2-T3 = 2 , T3 -T1 = 2

During star-up , as the compressor motor speed increases the amperage does what ? a. increases b. decreases c. stays about the same

decreases

A motor draws LRA only when the motor is mechanically locked up . a. True b. False

false

The contacts ( 1-2) of a potential relay are normally open (NO ) ? a. True b. False

false

What size compressors use current relays ? a. compressors over 1 hp b. compressors up to 3 Hp c. fractional horsepower compressors

fractional horsepower compressors

The amperage load rating of a compressor contactor is listed under which rating, the inducting rating or resistance load rating ? a. inductive load rating b. resistance load rating

inductive load rating

On a current relay, what do the terminal designations, , L, M, and S stand for ? a. line, main winding and start winding b. load, middle winding , and short winding c. line, minor winding and start winding

line , main winding and start winding

What are the two main weakness of 3 phase motors : a. wire size and circuit breaker size b. phase loss and voltage unbalance c. high amperage and low voltage

phase loss and voltage unbalance

What may be the problem with a single phase motor that starts and runs for a few seconds, but goes out on overload ? a. bad start capacitor b. start relay contacts stuck closed c. weak overload

start relay contacts stuck closed

What is a PTCR ? How does it open the circuit to the start winding ?

the PTC relay is a solid state relay, that increases its resistance to current flow when it heats up . When the compressor motor starts there is full power through the PTCR to the start winding. Within a few seconds the current draw of the compressor heats up the ceramic disc inside the relay. Heat transforms the conducting properties of the disc to an insulator. The material stops the flow of power to the start winding as effectively as the opening of a set of contacts , but without using moving mechanical parts.

On a 3 phase compressor, If the ohm reading for T1 - T2 , T2 - T3 , and T3 -T1 were all infinite resistance, What is the problem ? a. The compressor motor is shorted to ground. b. All the compressor windings have shorted open . c. The motor overload is open.

the motor overload is open.

The contactor must be replaced whenever a 3- phase compressor is replaced. a. T b. F

true

What are the 2 basic functions of a start relay ? a. A start relay provides full power to the start winding on start up , and then de-energizes the start windings when the motor is up to speed. b. The start relay provides full power to the start windings on start - up, and then provides a phase shift to keep the motor turning. c.The start relay provides a phase motor , then reverses the phase shift to keep the motor running .

A start relay provides full power to the start winding on start-up, and then de-energizes the start windings when the motor is up to speed.

Checking the start -up voltage at the compressor terminals can be dangerous. Why ? a. Because voltage must be checked with the power turned off. b. Because a slip of the meter probe could cause a short circuit. c. Because it is difficult to tell which is the start terminal and which is common.

Because a slip of the meter probe could cause a short circuit.

How is a potential relay checked with an ohmmeter ? a. The switch contacts (1-2) should be closed and the relay coil ( 5-2 ) should have measurable resistance . b. The switch contacts (1-2) should be open and the relay coil ( 5- 2 ) should have infinite resistance. c. The switch contacts ( 1-2) should be closed , and the relay coil ( 5-2 ) should have no resistance.

Te switch contacts ( 1-2 ) should be closed and the relay coil ( 5-2 ) should have measurable resistance.

What are considered the poles of a motor ? a. the rotor and stator b. the bundles of wires for the run windings , or for the start windings. c. the negative and positive fields of magnetic reactors.

The bundles of wires for the run windings, or for the start windings.

If a 3 phase compressor is getting full voltage, trying to start, but going out on an internal overload, what is the problem ? a. The compressor is grounded. b. The compressor winding are open . c.The compressor is mechanically seized, or locked up.

The compressor is mechanically seized, or locked up.

When replacing a capacitor , what is the rule about capacitor VAC ratings ? a. The new capacitor's VAC rating must be equal to , or greater than the capacitor it is replacing. b. The new capacitor's VAC rating must always be greater than the capacitor it is replacing. c. IF the MFD rating is the same as the original capacitor, the VAC can lower or higher than the original.

The new capacitors VAC rating must be equal to , or greater than the capacitor it is replacing.

How is the operation of a run cap different from that of a start cap ? a. A start cap has a higher VAC. b. A start cap remains in the circuit longer,, but a run cap has a lower MFD rating. c. The run capacitor remains in the circuit, but the start capacitor drops out after the compressor is up to speed.

The run capacitor remains in the circuit, but the start capacitor drops out after the compressor is up to speed.

How does a 1 phase motor accomplish its phase shift ? a. Voltage is delayed in order to energize the run winding sooner. b. A running winding is used to change the resistance when the motor starts. c. The start winding has more resistance which causes a phase shift, creating a slightly different angle to the magnetic pull of the stator.

The start winding has more resistance which causes a phase shift, creating a slightly different angle to the magnetic pull of the stator.

Why does a 1 phase motor need a phase shift to start the motor turning ? a. The windings are 120 degree out of phase and , therefore , difficult to realign. b. Single -phase motors do not have equal resistance ; they need something to equalize the phase shift. c. The windings are 180 degree out of phase; therefore, on start-up the stator and rotor have equal , but opposite attraction.

The windings are 180 degree out of phase; therefore, on start-up the stator and rotor have equal , but opposite attraction.

What indicates the contacts are bad on the contactor ? a. There is a voltage reading across the contacts of the contactor when pulled in. b. The contactor chatters or hums. c. There is 0 volts across the contacts of the contactor when pulled in.

There is a voltage reading across the contacts of the contactor when pulled in.

On a 3 phase compressor, if the ohm readings for T1 -T2 and T2 - T3 were each 3 ohms, and T3 -T1 winding is open . a. True b. False

True

Assume a technician has an emergency situation and needs a 15 u F x 370 VAC run capacitor. He has two of each of the following capacitors : 5 u F, 7.5 u F ,and 10 u F , all rated at 370 VAC. What combinations could he use and how would he wire them , in series or parallel ? a. Two 7.5 u F capacitors wired in series, and 5 u F wired in series. b. A 10 u F and a 5 u F capacitor wired in series, and a 7.5 u F wired in parallel. c. Two 7.5 u F capacitors wired in parallel, or a 10 u F and a 5 u F wired in parallel.

Two 7.5 u F capacitors wired in parallel , or a 10 u F and a 5 u F wired in parallel.

What formula is used to measure the percentage of voltage unbalance ? a. Vu= Va divided by ( Va + Vd ) b. Vu = Vd divided by Va c. Vu = Vd divided by ( Va + Vd )

Vu = Vd divided by Va

Why is it dangerous to dump out a compressor motor overload ? a. Without the overload, there is no motor protection. The motor could be damaged and the technician injured. b. It could trip the circuit breaker. c. The technician might short the overload while trying to disconnect it.

Without the overload, there is no motor protection. The motor could be damaged and the technician injured.

If a compressor start relay needs to be replaced, should the start capacitor be replaced as well ? Why or why not ? a. Yes, because a new capacitor always comes with a replacement relay. b. Yes, because if the relay fails, it is probably put a strain on the capacitor as well. c. No, because you should only replace what you know is bad.

Yes, because if the relay fails, it is probably put a strain on the capacitor as well .

What may bee the problem with a single phase motor that makes a humming sound, tries start , but goes out on overload ? a. bad start capacitor b. locked up compressor c. low voltage to the compressor d. all of the above

all of the above

Why does the cover of a compressor terminal box need to be left on ? a. Prevent hazards by fire if dirt and oil get into the control box. b. So the overload will properly since motor temperature and open during an overload condition. c. Prevents accidental contact with live wires by technician. d. all of the above

all of the above