Amazon Comissioning

Question 1

“Tell me about yourself”

Answer 1

I’m an electrical engineer with a strong focus on power systems, system integration, and safety-critical testing. My background includes hands-on lab and system-level work, AutoCAD experience, and troubleshooting electrical and electro-mechanical systems. I’m especially strong at breaking down complex systems, identifying failure points, and working across teams to make sure systems operate safely and reliably. I’m also very comfortable learning new systems quickly and applying documentation and specs directly in real test environments.

Question 2

How would you troubleshoot a power system issue in a data center?

Answer 2

I’d start by reviewing alarms and logs from the BMS or monitoring systems to localize the issue. Next, I’d verify the power distribution path — checking PDUs, breakers, and connections to ensure correct configuration. I’d then use measurement tools like multimeters or oscilloscopes to check voltage, continuity, and signal integrity. From there, I’d trace the power path back to the source to identify where the deviation occurs. Throughout the process, I’d prioritize safety procedures and document findings clearly.

Question 3

Conflict with stakeholders

Answer 3

S – The lead engineer and program manager disagreed on when and how batteries could be charged — specifically temperature limits, heater duration, and charging timing.
T – I needed to align technical safety requirements with program schedule needs.
A – I organized a meeting with all stakeholders, reviewed the battery specifications and heater requirements, and presented a clear, data-backed path forward. I facilitated discussion so both sides understood the risks and constraints.
R – We reached agreement on a charging procedure that met safety requirements and kept the program moving forward.

Question 4

Tight Deadline

Answer 4

S – We had a tight deadline to complete FlatSAT integration, but reaction wheels couldn’t be tested because their addresses were unknown.
T – I needed to identify the correct addresses quickly so testing could continue.
A – I wrote a script that iterated through all possible addresses, spun each reaction wheel to identify it, and mapped each device to its physical location. I then reprogrammed the addresses correctly.
R – We stayed on schedule, completed integration, and avoided delaying downstream testing.

Question 5

Cross-Functional Teamwork

Answer 5

S – During battery TVAC testing, multiple teams were involved: mechanical, thermal, and software.
T – My role was to ensure the system was test-ready across all disciplines.
A – I coordinated with the mechanical team to ensure structural integrity, worked with the thermal team to verify thermocouple placement and measurement coverage, and collaborated with the software team to confirm data collection and analysis were properly integrated.
R – The testing was completed successfully with accurate data and no mechanical or integration issues.

Question 6

Failure / Troubleshooting

Answer 6

S – While testing the PCDU and OBC together, communication failed initially.
T – I needed to restore communication so testing could proceed.
A – I reviewed the PCDU specification and noticed a star-grounding requirement. I connected the chassis of the power supply, PCDU, and OBC according to the grounding diagram.
R – Communication immediately began working, testing resumed, and the issue was resolved without hardware changes.

Question 7

What is A/B redundancy, and how do you validate it during commissioning?

Answer 7

A/B redundancy means the IT load is supported by two independent power paths. During commissioning, I validate it by performing failure testing on each path independently, verifying that the load remains supported without interruption when one side is lost.
Keywords:
Independent paths, failure testing, no single point of failure

Question 8

Walk me through the major components of a data center power system.

Answer 8

Utility power enters the facility and feeds switchgear. From there, power goes through UPS systems to provide conditioned, uninterrupted power. Generators provide backup during utility outages, typically through ATS systems. Power is then distributed through PDUs or RPPs to the IT load, usually in an A/B redundant configuration.

Keywords to hit:
Utility → Switchgear → UPS → Generators → ATS → PDU/RPP → IT load
A/B redundancy

Question 9

Walk me through commissioning a UPS system.

Answer 9

A:

I start by reviewing design intent and drawings. Then I verify installation, grounding, and inspections. Next, I perform pre-functional checks, followed by functional testing under load. I validate alarms, bypass operation, battery performance, and finally perform integrated testing with upstream and downstream systems.

Keywords:
Design intent, grounding, load testing, alarms, bypass, batteries

Question 10

What are common causes of UPS trips during commissioning?

Answer 10

A:

Common causes include incorrect breaker settings, grounding issues, overload conditions, incorrect sequencing, or configuration errors. I isolate the issue by reviewing logs, verifying settings, and testing subsystems individually before re-integrating.

Keywords:
Settings, grounding, overload, logs, isolate

Question 11

What is an ATS and how do you test it?

Answer 11

A:

An Automatic Transfer Switch transfers load between utility and generator power. During testing, I simulate loss of utility power, verify correct transfer timing, confirm stable generator operation, and ensure the load transitions back safely when utility is restored.

Keywords:
Transfer timing, generator stability, safe retransfer

Question 12

Q: How do you test generators without risking uptime?

Answer 12

A:

I follow approved procedures, confirm redundancy is available, notify stakeholders, and perform controlled testing using load banks or scheduled transfer tests. Safety and communication are critical.

Keywords:
Procedures, redundancy, load banks, communication

Question 13

What is IST and why is it important?

Answer 13

Integrated Systems Testing validates that multiple systems operate correctly together under real failure conditions. It’s important because many failures only appear when systems interact, not during isolated tests.

Keywords:
System interaction, failure scenarios, real-world validation

Question 14

What documentation is produced during commissioning?

Answer 14

Typical documentation includes pre-functional checklists, functional test procedures, test results, issue logs, as-built drawings, and final commissioning reports.

Keywords:
Checklists, results, as-builts, reports

Question 15

A data hall loses power — what do you do?

Answer 15

First, I ensure safety. Then I determine scope and impact, review alarms and logs, identify which power path failed, isolate the fault, and coordinate recovery. I document findings and corrective actions.

Keywords:
Safety first, scope, logs, isolate, recovery

Question 16

Why is grounding critical and how do you verify it?

Answer 16

Proper grounding ensures safety, stable reference points, and reliable communication. I verify grounding by reviewing design documents, inspecting physical connections, and testing continuity and impedance where required.

Keywords:
Safety, reference, continuity, impedance

Question 17

What risks do you watch for during commissioning?

Answer 17

Common risks include human error, misconfiguration, incomplete testing, poor communication, and inadequate documentation. I mitigate these through checklists, peer reviews, and controlled testing.

Keywords:
Human error, checklists, controlled testing

Question 18

How do you ensure safety in live environments?

Answer 18

I follow lockout/tagout procedures, verify system state before work, stop work if conditions are unsafe, and communicate clearly with all stakeholders.

Key phrase to memorize:

“I stop work immediately.”

Question 19

How do you commission a data center cooling system?

Answer 19

I start by reviewing design intent and control sequences. I verify installation and instrumentation, then perform pre-functional checks on components like CRAHs or CRACs. I validate airflow, temperature sensors, alarms, and control logic. Finally, I perform integrated testing to confirm the cooling system responds correctly to load changes and failure scenarios.
What they’re listening for:
Design intent → sensors → controls → failure response

Question 20

What’s the difference between CRAH and CRAC?

Answer 20

CRAC units use compressors and refrigerant to provide cooling, while CRAH units use chilled water supplied by a central plant. CRAHs are more common in large data centers because they’re more efficient and scalable.

Question 21

How do you test cooling redundancy?

Answer 21

I simulate failure of a cooling unit or pump and verify remaining systems maintain acceptable temperature and airflow. I monitor sensor data, alarms, and control responses to ensure redundancy works as designed.

Question 22

What do you do if cooling can’t keep up?

Answer 22

I first confirm sensor accuracy and airflow. Then I check control logic, valve or damper positions, and equipment status. If needed, I reduce load or stop testing to prevent thermal risk and coordinate corrective action.

Key phrase:

“Protect the equipment first.”

Question 23

What documentation is produced during commissioning?

Answer 23

Commissioning documentation typically includes pre-functional checklists, functional and integrated test procedures, recorded test results, issue or punch lists, as-built drawings, and a final commissioning report that documents system readiness and outstanding risks.