100+ Electrical Design Engineer Interview Questions and Answers

Cable sizing is calculated using the formula for voltage drop, which takes into account resistive and inductive drop. Voltage drop is limited to 5% to ensure efficient power transmission.

• Cable sizing is determined by calculating the voltage drop using the formula: VD = (I * L * R * 2) / 1000

• Resistive drop is calculated using Ohm's Law: Vr = I * R

• Inductive drop is calculated using the formula: Vi = I * X

• Voltage drop is limited to 5% to prevent excessive power loss and ensure e...read more

Explanation of lighting calculation, light loss factor, utilisation factor, and minimum lux required in substation.

• Lighting calculation involves determining the amount of light required in a space.

• Light loss factor is the reduction in light output due to factors such as dirt, dust, and aging of lamps.

• Utilisation factor is the ratio of light received by a surface to the total light output of the lamps.

• Formula for lighting calculation: Total light output = Area x Required lux l...read more

Percentage Impedance is a measure of the voltage drop in a transformer during a short circuit. It determines the ability of the transformer to withstand short circuit currents.

• Percentage Impedance is the ratio of the rated voltage of a transformer to the short circuit current at its terminals, expressed as a percentage.

• It represents the internal impedance of the transformer and is usually provided by the manufacturer.

• A higher percentage impedance means a higher voltage drop d...read more

The input required for a single line diagram includes information about the electrical system components and their connections.

• Information about the electrical system components such as generators, transformers, switchgear, and loads

• The connections between these components including the type of connection and the ratings of the equipment

• The voltage level of the system and the type of system grounding

• The protective devices such as circuit breakers and fuses

• Any special requirem...read more

Hazardous area classification involves categorizing areas based on the presence of flammable gases, vapors, or dusts.

• Hazardous areas are classified based on the likelihood of the presence of flammable substances.

• Temperature Class refers to the maximum surface temperature of equipment that can be used in a hazardous area.

• Hazardous areas are categorized into zones based on the frequency and duration of the presence of flammable substances.

• Examples of hazardous areas include oil...read more

Earthing calculation standards and resistances for substation and lightning protection.

• Earthing calculation involves determining the resistance of the earth electrode system.

• The standard used for earthing calculation is IEEE 80.

• The resistance in substation should be less than 1 ohm.

• The resistance for lightning protection should be less than 10 ohms.

• Factors affecting earthing calculation include soil resistivity, electrode material, and electrode spacing.

• Earthing calculation i...read more

OLR setting in a star-delta connection determines the transition point between star and delta mode.

• OLR stands for Overload Relay.

• In a star-delta connection, the motor is initially started in star mode to reduce the starting current.

• After a certain time, the motor is switched to delta mode for normal operation.

• The OLR setting determines the current threshold at which the transition from star to delta occurs.

• The OLR setting should be adjusted based on the motor's rated current ...read more

E-Plan, AutoCAD, and E-CAD are all software used in electrical design engineering, but they have differences.

• E-Plan is a specialized software for electrical engineering design and documentation.

• AutoCAD is a general-purpose computer-aided design (CAD) software used in various industries.

• E-CAD refers to the use of CAD software specifically for electronic design and circuit board layout.

• E-Plan focuses on electrical schematics, panel layouts, and wiring diagrams.

• AutoCAD is more v...read more

MCB, MCCB, and MPCB are circuit breakers used for electrical protection. They differ in their current ratings and trip characteristics.

• MCB stands for Miniature Circuit Breaker and is used for low current applications up to 125A.

• MCCB stands for Molded Case Circuit Breaker and is used for higher current applications up to 2500A.

• MPCB stands for Motor Protection Circuit Breaker and is used for protecting motors from overload and short circuit.

• MCBs are classified based on their tr...read more

The two earthing terminals in a motor provide redundancy and ensure safety in case of a fault.

• The first earthing terminal is connected to the motor frame, providing a path for fault current to flow and preventing electric shock to personnel.

• The second earthing terminal is connected to the motor winding, providing a path for fault current to flow and protecting the motor from damage.

• Having two earthing terminals ensures redundancy, so that even if one connection fails, the oth...read more

Motor feeder and power feeder requirements are essential for electrical design engineers to ensure proper functioning of electrical systems.

• Motor feeder requirements include selecting the appropriate motor size, voltage, and current rating.

• Power feeder requirements involve determining the load requirements and selecting the appropriate cable size and voltage drop.

• Proper coordination and protection devices such as circuit breakers and fuses must be selected for both motor and ...read more

The motor contribution to the short circuit current is significant and needs to be considered in electrical design.

• The motor's impedance affects the short circuit current level.

• The motor's starting current can cause a significant increase in short circuit current.

• The motor's location in the electrical system can affect its contribution to the short circuit current.

• The motor's size and type can also impact its contribution to the short circuit current.

• Proper coordination and p...read more

APFC stands for Automatic Power Factor Correction. Series reactor is a device used to limit current flow.

• APFC is a system that automatically corrects the power factor of an electrical network.

• It uses capacitors to improve the power factor and reduce energy consumption.

• Series reactor is a device that is used to limit the flow of current in a circuit.

• It is used to protect equipment from overvoltage and to reduce harmonics in the system.

• An example of series reactor is a line rea...read more

Lux levels are calculated using the formula Lux = Lumens / Area (in square meters). Required lux levels vary depending on the specific application.

• Lux levels are calculated by dividing the total lumens of light by the area in square meters that the light is illuminating.

• For roads, recommended lux levels range from 10 to 20 lux for residential streets to 50 to 100 lux for highways.

• Workstations typically require lux levels between 300 to 500 lux for general office work, and up ...read more

The process for preparing a Single Line Diagram (SLD) involves identifying all electrical components and their connections.

• Identify all electrical components in the system

• Determine the connections between the components

• Represent the components and connections using standardized symbols

• Include power sources, distribution panels, transformers, circuit breakers, switches, and loads

• Ensure the diagram is clear, organized, and easy to understand

Sizing a cable tray involves considering the number and type of cables, environmental conditions, and support spacing. Cable trays are classified by material (steel, aluminum, fiberglass) and size (light duty, medium duty, heavy duty).

• Consider the number and type of cables to be installed in the cable tray

• Take into account environmental conditions such as temperature, moisture, and corrosive elements

• Determine the support spacing based on the weight of the cables and tray mate...read more

The cable size and circuit breaker rating for a 50KW motor at 30m distance from the panel depend on factors like voltage, current, and installation conditions.

• Calculate the full load current (FLC) of the motor using the formula: FLC = (Power (kW) * 1000) / (sqrt(3) * Voltage)

• Select a cable size based on the FLC, voltage drop considerations, and installation conditions

• Choose a circuit breaker rating based on the FLC and the motor's starting current requirements

• Consider factors...read more

Short circuit current from 1000kVA TF (5% Z) on a panel and determine its CB Fault current rating using IEC Standard.

• Calculate the short circuit current using the formula: Short circuit current = 1000kVA / (1.732 * 5%)

• Determine the CB Fault current rating based on the calculated short circuit current

• Refer to IEC Standard for guidelines on short circuit current calculations and CB ratings

The voltage in a 3-phase system is typically 415 volts.

• The voltage in a 3-phase system is higher than in a single-phase system.

• In industrial and commercial applications, the standard voltage for a 3-phase system is 415 volts.

• Other common voltages for 3-phase systems include 208 volts and 480 volts.

• The voltage between any two phases in a 3-phase system is equal to the line voltage.

• The voltage between any phase and the neutral in a 3-phase system is equal to the phase voltage.

Protection schemes for transformers and generators.

• Overcurrent protection

• Differential protection

• Distance protection

• Restricted earth fault protection

• Backup protection

• Buchholz relay protection

• Thermal overload protection

• Under/over voltage protection

• Neutral grounding protection

Fault current for primary and secondary side of transformer can be calculated using Ohm's law and transformer impedance.

• Determine the transformer impedance

• Calculate the voltage drop across the impedance

• Use Ohm's law to calculate the fault current

• For primary side, use the voltage rating of the transformer

• For secondary side, use the voltage rating of the load

• Consider the type of fault (3-phase, single-phase, ground fault) and the system configuration

• Example: Primary side fault ...read more

Eplan Electric allows generating various reports for electrical design projects.

• Reports can be generated for bills of materials, cable lists, terminal diagrams, and more.

• Reports can be customized to include specific information and formatting.

• Reports can be exported in various file formats, including Excel, PDF, and XML.

• Reports can be generated for individual pages or for the entire project.

• Reports can be scheduled to run automatically at specific intervals.

• Examples of report...read more

A rig platform is a structure used in offshore drilling operations to support drilling equipment and personnel.

• Rig platforms are typically located in bodies of water and are used for extracting oil and gas from beneath the seabed.

• They provide a stable base for drilling rigs, equipment, and crew to operate in harsh offshore environments.

• Rig platforms can be fixed (attached to the seabed) or floating (anchored to the seabed or kept in position by dynamic positioning systems).

For making LOP, the required data includes the electrical load details, power supply specifications, circuit layout, and safety regulations.

• Electrical load details such as the type of equipment, power rating, and operating voltage are necessary.

• Power supply specifications like the voltage level, frequency, and phase configuration are important.

• The circuit layout, including the arrangement of components, wiring, and connections, is required.

• Safety regulations and standards mus...read more

Important technical data for transformers and motors include voltage, current, power rating, efficiency, and temperature rise.

• Voltage rating

• Current rating

• Power rating

• Efficiency

• Temperature rise

Clearance between cable tray and wet service pipe is maintained by using appropriate support systems and ensuring proper spacing.

• Use support systems such as clamps, hangers, and brackets to secure the cable tray and wet service pipe at appropriate distances.

• Ensure proper spacing between the cable tray and wet service pipe to prevent any contact or interference.

• Follow industry standards and regulations for minimum clearance requirements between different services.

• Regularly ins...read more

Exit sign lighting in corridors or pathways is designed to provide clear and visible guidance to occupants in case of emergency.

• Ensure exit signs are placed at all exits and change in direction

• Use photoluminescent materials for backup in case of power failure

• Provide adequate lighting levels to ensure visibility in all conditions

• Consider using LED lights for energy efficiency and long lifespan

Load list preparation involves identifying all electrical loads in a system and determining their power requirements to size transformers.

• Identify all electrical loads in the system, including lighting, equipment, HVAC, etc.

• Determine the power requirements of each load in terms of voltage, current, and power factor.

• Sum up the power requirements of all loads to calculate the total load on the system.

• Select an appropriate transformer size based on the total load and any future ...read more

A Variable Frequency Drive (VFD) is a type of motor controller that drives an electric motor by varying the frequency and voltage supplied to the motor.

• VFDs are used to control the speed and torque of AC induction motors.

• They convert fixed frequency and voltage input to variable frequency and voltage output.

• VFDs improve energy efficiency by matching motor speed to the actual load requirements.

• They are commonly used in HVAC systems, pumps, conveyors, and other industrial appli...read more

Designing a CCTV system involves selecting appropriate cameras, DVR/NVR, and cables based on requirements.

• Determine the coverage area and required resolution for each camera

• Select suitable cameras (e.g. dome, bullet, PTZ) based on the environment

• Choose a DVR/NVR with enough storage capacity and network connectivity

• Use high-quality coaxial cables (e.g. RG59) for analog cameras or Ethernet cables for IP cameras

• Consider using power over Ethernet (PoE) for easier installation

Harmonics in transformers are non-linear currents or voltages that can cause overheating, increased losses, and interference in electrical systems.

• Harmonics are multiples of the fundamental frequency in the power system, typically caused by non-linear loads like variable frequency drives or rectifiers.

• Impacts of harmonics include increased heating in transformers, higher losses, reduced power quality, and interference with communication systems.

• To reduce harmonics, methods su...read more

RTD stands for Resistance Temperature Detector. PT100 is a type of RTD that has a resistance of 100 ohms at 0 degrees Celsius.

• RTD stands for Resistance Temperature Detector.

• RTDs are sensors used to measure temperature by correlating the resistance of the RTD element with temperature.

• PT100 is a type of RTD that has a resistance of 100 ohms at 0 degrees Celsius.

• PT1000 is another type of RTD that has a resistance of 1000 ohms at 0 degrees Celsius.

• Other types of RTDs include PT50...read more

Di/Dos & Ai/Aos are input/output signals used in PLC programming for digital and analog signals.

• Di/Dos refer to digital inputs/outputs, used for binary signals like on/off switches

• Ai/Aos refer to analog inputs/outputs, used for continuous signals like temperature or pressure sensors

• Di/Dos are typically represented by discrete bits in PLC programming

• Ai/Aos are represented by analog values in PLC programming

• Examples: Di - a limit switch detecting a door open/close status, Ai - ...read more

The data required for making CSD includes specifications, schematics, component datasheets, and design constraints.

• Specifications of the electrical system

• Schematics of the circuit design

• Datasheets of the components being used

• Design constraints and requirements

HV switchgears are devices used to control, protect and isolate electrical equipment in high voltage power systems.

• Air-insulated switchgear (AIS)

• Gas-insulated switchgear (GIS)

• Hybrid switchgear

• Vacuum circuit breaker (VCB)

• Sulfur hexafluoride (SF6) circuit breaker

• Oil circuit breaker (OCB)

Voltage is the potential difference between two points in an electrical circuit, while current is the flow of electric charge through a conductor.

• Voltage is measured in volts (V) and current is measured in amperes (A).

• Voltage is the driving force that pushes current through a circuit.

• Ohm's Law states that voltage is equal to current multiplied by resistance (V=IR).

• Voltage can be stepped up or down using transformers, while current cannot.

• In a series circuit, the current is th...read more

The standards followed for cable trays are typically NEMA VE 1 and NEC, while the standards for earthing include IEEE 80 and IEC 60364.

• Cable trays are usually designed according to NEMA VE 1 and NEC standards.

• Earthing systems are typically designed following IEEE 80 and IEC 60364 standards.

• Compliance with these standards ensures safety, reliability, and proper functioning of electrical systems.

• For example, NEMA VE 1 provides guidelines for cable tray installation, while IEEE ...read more

CT and PT are used for current and voltage measurement respectively. Primary winding is connected to the source and secondary to the load.

• CT measures the current flowing in a circuit and steps down the current to a level that can be measured by an ammeter

• PT measures the voltage of a circuit and steps down the voltage to a level that can be measured by a voltmeter

• Primary winding is connected to the source and secondary winding is connected to the load

• CT and PT are used in powe...read more

Capacitor is used to reduce noise and improve the response time of photo diode.

• Capacitor helps in filtering out high-frequency noise from the output signal of photo diode.

• It also helps in improving the response time of the photo diode by reducing the effect of capacitance in the circuit.

• The value of the capacitor used depends on the frequency of the noise and the response time required.

• For example, in a photodetector circuit, a capacitor of 0.1uF can be used to reduce noise a...read more

MCC panel stands for Motor Control Center panel. Types of starters include DOL, star-delta, and soft starter.

• MCC panel is a type of electrical control panel that houses motor starters, drives, and other control equipment.

• Types of starters include Direct-On-Line (DOL), Star-Delta, and Soft Starter.

• DOL starter provides full voltage to the motor upon start, while star-delta starter reduces the voltage during start to minimize current.

• Soft starter gradually increases the voltage ...read more

MCB stands for Miniature Circuit Breaker and MCCB stands for Molded Case Circuit Breaker. They are used for electrical protection.

• MCB is a type of circuit breaker that automatically switches off electrical circuits during abnormal conditions such as overload or short circuit.

• MCCB is a type of circuit breaker that provides protection against overloads, short circuits, and ground faults.

• MCBs are commonly used in residential and commercial buildings to protect electrical circuit...read more

Selection of wires, connectors, fuses, and coverings for wiring harness involves considering factors such as current rating, voltage drop, temperature, and environmental conditions.

• Determine the current rating and voltage drop requirements for the application

• Select wires with appropriate gauge size and insulation material

• Choose connectors based on the number of wires, current rating, and environmental conditions

• Select fuses based on the current rating and voltage rating of th...read more

Voltage drop in cable can be calculated using Ohm's law and considering the cable length, current, and resistance.

• Determine the length of the cable

• Determine the current flowing through the cable

• Determine the resistance of the cable

• Use Ohm's law (V = IR) to calculate the voltage drop

• Select a cable size that will limit the voltage drop to an acceptable level

Designing an electrical system involves determining power requirements, selecting components, creating schematics, and ensuring safety.

• Determine power requirements based on the load and usage

• Select appropriate components such as transformers, circuit breakers, and wires

• Create schematics and diagrams to illustrate the system

• Ensure safety by following codes and regulations

• Consider maintenance and future expansion needs

The IP rating of a panel refers to its level of protection against solids and liquids. Panels can be separated by physical barriers or electrical insulation.

• IP rating indicates the degree of protection provided by a panel against dust and water. Higher IP ratings offer better protection.

• Separation of panels can be achieved through physical barriers such as walls, partitions, or enclosures.

• Electrical insulation is another form of separation, where panels are isolated from each...read more

NEC codes dictate wire sizing, load calculation, breaker sizing, and disconnect sizing for electrical design.

• NEC 310-16 provides guidelines for wire sizing based on ampacity and temperature rating

• NEC 220 provides guidelines for load calculation based on the type of building and its intended use

• NEC 240 provides guidelines for breaker sizing based on the wire size and load calculation

• NEC 430 provides guidelines for disconnect sizing based on the motor's full load current

• Complia...read more

Softwares used in Electrical Engineering include CAD, simulation, and analysis tools.

• CAD software like AutoCAD and SolidWorks are used for designing electrical systems and components

• Simulation software like MATLAB and Simulink are used to model and simulate electrical systems

• Analysis software like ETAP and PSCAD are used to analyze and optimize electrical systems

• Other software like LabVIEW and Altium Designer are also used in Electrical Engineering