Question 1

How do you approach sizing a circuit breaker and conductor for a given load?

Accepted Answer

I calculate the continuous load current, apply the 125% factor per NEC for continuous loads, then size the conductor for ampacity and the breaker to protect it, checking voltage drop stays under about 3% for branch circuits. I also verify the conductor and breaker combination matches, since an oversized breaker won't protect an undersized wire.

Question 2

Walk me through how you'd troubleshoot a circuit that keeps tripping its breaker.

Accepted Answer

I first check for an obvious short or ground fault with a megohmmeter, then measure actual load current against the breaker rating to rule out simple overload before suspecting a wiring fault. I isolate sections of the circuit systematically rather than randomly swapping components.

Question 3

How do you calculate voltage drop for a long conductor run and what do you do if it exceeds limits?

Accepted Answer

I use the conductor's resistance per unit length, the current, and the run length to calculate drop, comparing it against the 3% branch circuit and 5% total guideline from NEC recommendations. If it's too high I upsize the conductor rather than just accepting the loss, since it affects both equipment performance and energy waste.

Question 4

Describe your process for performing an arc flash hazard analysis.

Accepted Answer

I gather the system's fault current and clearing time data, then calculate incident energy at each equipment location per IEEE 1584, which determines the required PPE category and boundary distances. I make sure the resulting labels are actually posted on the equipment, since the analysis is only useful if the field crew can see it.

Question 5

How do you approach designing a grounding system for a facility?

Accepted Answer

I follow NEC Article 250 requirements for grounding electrode conductors and bonding, ensuring low-impedance paths back to the source, and I test the final ground resistance, typically targeting under 25 ohms for a single electrode. Proper grounding is what makes overcurrent protection actually work correctly during a fault.

Question 6

What's your process when commissioning a new piece of equipment before it goes live?

Accepted Answer

I verify all connections against the as-built drawings, perform insulation resistance and continuity testing before energizing, and do a controlled startup with the equipment isolated from load initially. Skipping insulation testing before first energization risks damaging equipment on a fault that testing would have caught.

Question 7

How do you handle a situation where you find an existing installation that's out of code compliance during a project?

Accepted Answer

I document it clearly with photos and code references, and flag it to the client and AHJ as appropriate rather than just quietly working around it, since liability follows anyone aware of a hazard. Whether it gets fixed immediately depends on severity, but I don't let it go unreported.

Question 8

Walk me through how you'd size a transformer for a new electrical service.

Accepted Answer

I calculate the total connected load with appropriate demand factors per NEC Table 220, add margin for future growth typically 20 to 25%, then select a standard transformer size that covers that kVA requirement. Undersizing based only on current load ignores the cost of a service upgrade a few years later.

Question 9

How do you approach power factor correction for an industrial facility with a low power factor penalty?

Accepted Answer

I calculate the existing power factor from utility billing data, size capacitor banks to bring it up to around 0.95, and check for resonance risk with any variable frequency drives already on site before installing. Correcting power factor without checking for harmonics can actually create new problems.

Question 10

Describe how you coordinate protective device settings across a distribution system.

Accepted Answer

I build a time-current coordination study so upstream breakers trip after downstream ones for a fault, minimizing the outage to just the affected circuit rather than the whole building. Poor coordination is a common cause of nuisance outages that affect far more equipment than the actual fault required.

Electrical Engineer interview questions and sample answers

Job-specific questions

1. How do you approach sizing a circuit breaker and conductor for a given load?

2. Walk me through how you'd troubleshoot a circuit that keeps tripping its breaker.

3. How do you calculate voltage drop for a long conductor run and what do you do if it exceeds limits?

4. Describe your process for performing an arc flash hazard analysis.

5. How do you approach designing a grounding system for a facility?

6. What's your process when commissioning a new piece of equipment before it goes live?

7. How do you handle a situation where you find an existing installation that's out of code compliance during a project?

8. Walk me through how you'd size a transformer for a new electrical service.

9. How do you approach power factor correction for an industrial facility with a low power factor penalty?

10. Describe how you coordinate protective device settings across a distribution system.

Behavioral questions

11. Tell me about a result you are proud of.

12. Describe a time you improved how something was done.

13. Tell me about a time you had to deliver under pressure.

14. Give an example of working with a difficult colleague or customer.

15. What is something you learned from a mistake?

Before the interview

Interview questions for related jobs