electrical_interview_prep_questions_answered_

Question 1

What is the difference between a delta and wye (Y) configuration?

Answer 1

• Wye: Line voltage is higher than phase voltage by square root of 3 (1.73)
• Delta: Line voltage and phase voltage are equal
• Phase Voltage: Voltage across a single winding
• Line Current: In Wye, equals phase current; in Delta, line current is higher than phase current

Delta offers higher reliability in phase failure; Wye offers flexibility but is more susceptible to voltage imbalances.

Question 2

What is the Line-to-Line Voltage (VLL)?

Answer 2

Voltage measured between any two phases in a three-phase system

Generally higher than line-to-neutral voltage due to phase separation of 120 degrees.

Question 3

What is the Line-to-Neutral Voltage (VLN)?

Answer 3

Voltage measured between one phase and the neutral point of the system

Represents the voltage available to a single-phase load.

Question 4

What is the difference between neutral and ground?

Answer 4

• Neutral: Carries current back to the power source
• Ground: Safety route used in cases of fault

Both serve different purposes in electrical systems.

Question 5

What does the WIDE mnemonic stand for?

Answer 5

• Width
• Height
• Depth
• Area

Used for dimensional measurements.

Question 6

What is the voltage read between one leg of a 480V – 3 phase system grounded in a Wye (Y) configuration?

Answer 6

277 volts

Calculated as 480V divided by square root of 3.

Question 7

What is ground fault protection?

Answer 7

An electrical safety system designed to prevent electric shock, equipment damage, and fire hazards

Detects leakage currents and interrupts power when necessary.

Question 8

If a fuse is ‘good’, what voltage read will you get across the installed fuse in a 120V system?

Answer 8

0 volts

The potential difference of voltage between the two points is 0.

Question 9

What is a megger used for?

Answer 9

Test the insulation of material

Essential for ensuring electrical safety.

Question 10

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

Answer 10

Switch 2 of the phases

This will reverse the motor direction.

Question 11

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

Answer 11

7,200 watts

Calculated using the formula: Max Watt = Amp Breaker capacity x 0.8.

Question 12

How do semiconductors work?

Answer 12

Materials with properties between conductors and insulators

Used in electronic devices to control the flow of electricity.

Question 13

What is pulse width modulation?

Answer 13

Technique to control power delivered to an electrical device by varying the width of pulses

Commonly used in motor control and LED brightness adjustment.

Question 14

What does VFD stand for?

Answer 14

Variable Frequency Drive

Controls the speed and performance of a motor.

Question 15

What does CT stand for and what does it do?

Answer 15

Current Transformer

Measures high current safely by converting it into manageable currents.

Question 16

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

Answer 16

0.5 amps

Calculated using the formula: Amps = watts / volts.

Question 17

Electrical fuses are rated in what?

Answer 17

• Voltage
• Current
• Time

Indicates how much voltage a fuse can safely interrupt, max current it can carry, and how quickly it will blow.

Question 18

What does the term AWG refer to?

Answer 18

American Wire Gauge

Standardized system to measure the diameter of round, solid, electrically conducting wires.

Question 19

What happens to voltage in a series circuit?

Answer 19

Voltage is the sum of the loads

Voltage is split between each load, lowering the voltage for each component.

Question 20

What is a UPS and what are its four major components?

Answer 20

• Battery: Stores charge
• Rectifier: Transforms AC to DC
• Inverter: Converts DC to AC
• Surge Protector: Protects from voltage surges

Uninterruptable Power Supply provides backup power.

Question 21

What types of UPS systems are there?

Answer 21

• Standby
• Line-Interactive
• Online Double Conversion

Each type has different operational characteristics and applications.

Question 22

If one of the components in a UPS system fails, can other components still power the load?

Answer 22

Yes

UPS systems are designed with redundancy to allow power transfer to bypass the failed component.

Question 23

How do you perform maintenance on a UPS?

Answer 23

• Visual inspection
• Monitoring load levels
• Temperature checks
• Battery terminal checks
• Runtime tests
• Servicing

Ensures the UPS operates effectively.

Question 24

What is a static switch?

Answer 24

Device that performs switching operations without moving parts

Utilizes power semiconductor devices for fast-acting applications.

Question 25

How does an **Automatic Transfer Switch (ATS)** operate?

Answer 25

Automatically switches between utility power and backup power source during outages ## Footnote Ensures continuous power supply.

Question 26

What are **paralleling requirements**?

Answer 26

* Equal Length * Same Material * Same Size * Same Insulation Type * Same Termination ## Footnote Ensures safe and effective operation of parallel conductors.

Question 27

What indicates that you are **'in phase'**?

Answer 27

* Same Frequency * Same Phase * Perfect Synchronization ## Footnote Essential for proper operation of electrical systems.

Question 28

What is required for **generator action**?

Answer 28

* Mechanical Energy Input * Engine Operation * Alternator Function * Voltage Regulation * Cooling and Exhaust * Control Panel ## Footnote These components work together to convert mechanical energy into electrical energy.

Question 29

How do you **increase the output voltage** on a generator?

Answer 29

Adjust the voltage regulator ## Footnote This maintains the desired voltage level.

Question 30

What is the standard **frequency** for a generator to run in the US?

Answer 30

60 Hz ## Footnote This frequency is standard for most electrical systems.

Question 31

How do we maintain the **speed of the generator** even with an increase/drop in load?

Answer 31

The generator control system adjusts the output ## Footnote Ensures frequency remains constant.

Question 32

What is the **RPM** of a generator rated at **480, 60 HZ, 4 poles**?

Answer 32

1800 RPM ## Footnote Calculated using the formula: RPM = (2 × 60 × Hz) / P.

Question 33

What voltage do you measure from **A to B** on a **Delta** transformer in a 480V system?

Answer 33

480 volts ## Footnote This is the phase-to-phase voltage.

Question 34

What voltage do you measure from **A to B** on a **Wye** transformer?

Answer 34

277 volts ## Footnote This is the phase-to-neutral voltage.

Question 35

What is the voltage read from **hot to neutral**, **hot to ground**, and **ground to neutral** in a household outlet?

Answer 35

* Hot to Neutral: 115V to 125V * Hot to Ground: Around 120V * Ground to Neutral: Approximately 0V ## Footnote Indicates a functioning circuit and proper grounding.

Question 36

If you had a **60-watt bulb** hooked up to a household outlet, how many amps would that lamp be using?

Answer 36

0.5 amps ## Footnote Calculated using the formula: Amps = watts / volts.

Question 37

If you ran **120V** across a fuse, is that fuse good or bad?

Answer 37

The fuse is good ## Footnote If it was bad, you could not run any volts through it.