Burns & McDonnell Senior Electrical Engineer Interview Questions and Answers

Load density refers to the amount of power consumed per unit area or volume.

• Load density is typically measured in watts per square meter or watts per cubic meter.

• It is used in electrical design to determine the distribution of power consumption in a given space.

• Higher load density may require more robust electrical systems to handle the increased power demand.

• For example, data centers have high load density due to the ...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 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...read more

CRI stands for Color Rendering Index, a measure of how accurately a light source illuminates colors compared to natural light.

• CRI is a scale from 0 to 100, with higher values indicating better color rendering.

• It is important in lighting design to ensure colors appear true and vibrant.

• LED lights typically have high CRI values, making them popular for applications where color accuracy is crucial.

UGR stands for Unified Glare Rating, a measure of the discomfort glare perceived by an observer.

• UGR is used in lighting design to evaluate the visual comfort of lighting installations.

• It takes into account factors such as the luminance of the light source, the position of the observer, and the reflectance of the surrounding surfaces.

• Lower UGR values indicate less glare and better visual comfort for the occupants.

• For ex...read more

Uniformity factor is a measure of how evenly distributed light is in a given space.

• Uniformity factor is calculated by dividing the minimum illuminance level by the average illuminance level in a space.

• A higher uniformity factor indicates more even lighting distribution.

• Uniformity factor is important in lighting design to ensure consistent lighting levels throughout a space.

• For example, in an office setting, a uniformit

Maintenance factor is a multiplier used in lighting design to account for the decrease in light output over time due to dirt, aging, and other factors.

• Maintenance factor is typically a value between 0 and 1, with 1 indicating no decrease in light output over time.

• It is used to adjust the initial illuminance level calculated for a space to account for the decrease in light output over the life of the lighting system.

• Fac...read more

Reflection index in rooms refers to the amount of sound reflected off surfaces within a room.

• Reflection index is important in determining the acoustics of a room.

• High reflection index can lead to echoes and reverberation.

• Materials like concrete and glass have high reflection index, while soft materials like carpets and curtains have low reflection index.

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

Earthing design involves creating a low-resistance path for fault currents to safely dissipate into the ground.

• Determine the type of earthing system needed based on the specific requirements of the electrical installation.

• Calculate the required size of the earthing conductors based on the fault current levels and soil resistivity.

• Ensure proper bonding of all metallic structures and equipment to the earthing system to p...read more

Earth loop impedance is the total impedance of the earth fault current path in an electrical circuit.

• Earth loop impedance is important for ensuring the safety of electrical installations.

• It is measured in ohms and is used to calculate the maximum fault current that could flow in the event of a fault.

• Low earth loop impedance is desirable as it helps to quickly trip circuit breakers in case of a fault.

• It is influenced by...read more

Designing a transformer room involves considering safety, space requirements, ventilation, and electrical codes.

• Ensure proper ventilation to prevent overheating of transformers

• Follow electrical codes and regulations for clearances and access

• Provide adequate space for maintenance and operation of transformers

• Consider safety measures such as fire protection and emergency shutdown systems

Cable tray sizing involves considering the current carrying capacity, voltage drop, and environmental factors.

• Calculate the total current carrying capacity required for the cables in the tray.

• Consider the voltage drop limitations based on the distance and load.

• Take into account the environmental factors such as temperature, humidity, and corrosive elements.

• Select the appropriate size and material of the cable tray base...read more

Spacing between smoke detectors depends on the type of detector and the manufacturer's recommendations.

• Spacing between smoke detectors is typically around 30 feet in residential areas.

• For high ceilings, detectors may need to be spaced closer together.

• Consult the manufacturer's guidelines for specific spacing requirements.

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 clear...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 u...read more

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 ...read more