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Chief Study Guide > Electrical > Flashcards

Electrical Flashcards

1
Q

What is the voltage read between one leg of 480V - 3 phase and ground?

A

277 volts

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2
Q

What is the difference between a motor starter and a contactor?

A

Motor starter has overload heaters

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3
Q

What is ground fault protection?

A

Senses any ground leakage and opens circuit.

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4
Q

What are several causes of high running amps on an air handler?

A

Bad bearings, belt too tight, alignment out.

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5
Q

What is the term “Locked Rotor Amps”?

A

Current draw with rotor standing still (upon startup)

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6
Q

If you read voltage with a voltmeter across a fuse while it is still installed, is the fuse good or bad?

A

Bad

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7
Q

What is a megger used for?

A

Test insulation resistance

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8
Q

How would you correct a newly installed 3 phase motor that was found to be running backwards?

A

Check phase rotation. Switch A and B phase

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9
Q

What is the max load you should put on a single pole 30 amp breaker?

A

24 amps (80%)

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10
Q

What is a VFD?

A

Variable Frequency Drive

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11
Q

What does CT stand for and what does it do?

A

Current Transformer. It measures amperage

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12
Q

How many amps does a standard 60 watt 120 volt light bulb use?

A

.5 amps. Amps = Watts / Volts

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13
Q

Electrical Fuses are rated in what?

A

Amps and Time

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14
Q

What is the difference between KW and KVA?

A

Power Factor is used in KW and not in KVA.

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15
Q

If I told you that a system was rated at a .8 Lagging Power Factor can you tell me what that indicates.

A

It is rated to run with the Current lagging the voltage due to having a higher Inductive Reactance. (As opposed to Capacitive Reactance or a pure resistive load.) They could also describe how reactance causes the relationship between the voltage and current to change.

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16
Q

What does the term AWG refer to?

A

American Wire Gauge.

17
Q

What is the purpose of a transistor?

A

A transistor is a semiconductor device which is commonly used to amplify or switch electronic signals. A transistor is made of a solid piece of a semiconductor material, with at least three terminals for connection to an external circuit. It is used as a switch or a signal amplifier in a circuit.

18
Q

The bridge used for measurement of inductance is

A

Anderson Bridge

19
Q

What is impedance?

A

The opposition to the flow of current in an AC circuit

20
Q

What is reactance?

A

Opposition to the flow of alternating current caused by capacitance or inductance

21
Q

How Does a Battery Work? and How does a battery charge?

A
  • Battery has got two leads,one positive and other negative.Electrons gather at the negative terminal of the battery and if you connect a wire across negative to positive,then the electrons from negative end will quickly flow through the wire to the positive terminal.Normally you will have a load connected in the wire which reduces the flow of electrons like a bulb or motor.
  • Inside the battery itself, a chemical reaction produces the electrons. The speed of electron production by this chemical reaction (the battery’s internal resistance) controls how many electrons can flow between the terminals. Electrons flow from the battery into a wire, and must travel from the negative to the positive terminal for the chemical reaction to take place.
22
Q

Transformer core are laminated for what purpose?

A

Reduce eddy current losses

23
Q

The Frequency is measured by _________ bridge?

A

wiens bridge

24
Q

Hays bridge is used to measure___________ and Schering bridge is used to measure____________

A

Inductance, Capacitance

25
Q

What does AC and DC stand for in the electrical field?

A

Alternating Current and Direct Current

26
Q

What is a Surge suppressor?

A
27
Q

What happens to voltage in a series circuit?

A

Voltage drops off at each device. While the current remains the same

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