Q: A 15kW 3-phase motor keeps overheating and tripping thermal relay. The line is down with high production pressure. How would you troubleshoot?

LOTO safety -> Measure 3-phase current (balanced? over-rated?) -> Check voltage, phase loss -> Motor: megger > 1MΩ, winding resistance -> Load: seized bearing, jammed conveyor -> Thermal relay. LOTO must be mentioned first. Most common cause: single phasing. Clamp meter and megger are mandatory tools.

Question 1

Please introduce yourself, your background and experience in electrical/electronics/automation. What industrial systems or automation lines have you worked with?

Accepted Answer

Education summary -> Experience (PLC, SCADA, panels, distribution) -> Core skills -> Reason for applying. Mention PLC brands you've worked with immediately. State certifications if any. If you have FDI experience, emphasize international standards (IEC, NEC).

Question 2

Describe your experience designing and wiring industrial electrical panels. What systems, capacity, and standards?

Accepted Answer

Panel types (MDB/DB, PLC, MCC, ATS) -> Capacity, voltage -> Standards (IEC 61439, NEC) -> Process -> Software (EPLAN). Mention specific brands (Schneider, ABB, Siemens). Know short circuit calculations, CB selection by Icu/Ics. FDI factories require IEC 61439.

Question 3

Do you have experience building preventive maintenance plans for factory electrical systems? Describe KPIs you track.

Accepted Answer

Classify equipment by criticality -> PM schedule -> KPIs: MTBF, MTTR, unplanned downtime %, PM compliance rate. Distinguish PM (time-based), PdM (condition-based), and RCM. Thermography effectively detects loose connections. FDI factories use SAP PM or Maximo.

Question 4

Explain differences between PLC programming languages per IEC 61131-3 (Ladder, ST, FBD). When to choose each, and what PLC brands have you used?

Accepted Answer

Ladder (visual, discrete) -> Structured Text (complex calculations, PID) -> FBD (analog, continuous data) -> Experience: Siemens TIA Portal, Allen Bradley Studio 5000, Mitsubishi GX Works. Siemens and Mitsubishi are most common at Japanese/Korean/European FDI factories in VN, Allen Bradley at American ones. Prepare real code examples.

Question 5

What is SCADA and what components make up factory SCADA architecture? What HMI design principles do you follow?

Accepted Answer

Architecture: Field devices -> PLC/RTU -> Communication -> SCADA Server -> HMI -> Historian. HMI design per ISA-101: high-performance graphics, grayscale background. Employers want to see full architecture understanding. Know OPC UA - the Industry 4.0 protocol. OT cybersecurity (IEC 62443) is increasingly valued by FDI factories.

Question 6

Explain the 3-phase electrical system in industrial plants. Why 3-phase over single-phase? What is power factor and how to improve it?

Accepted Answer

3-phase: 3 sine waves 120 degrees apart -> Advantages: higher efficiency, better motors -> Power factor: low PF means penalties -> Improvement: capacitor banks, VFDs. EVN heavily penalizes PF < 0.85. Know load calculations, cable selection per IEC 60364. Harmonic knowledge from VFDs and filtering is advanced.

Question 7

A 15kW 3-phase motor keeps overheating and tripping thermal relay. The line is down with high production pressure. How would you troubleshoot?

Accepted Answer

LOTO safety -> Measure 3-phase current (balanced? over-rated?) -> Check voltage, phase loss -> Motor: megger > 1MΩ, winding resistance -> Load: seized bearing, jammed conveyor -> Thermal relay. LOTO must be mentioned first. Most common cause: single phasing. Clamp meter and megger are mandatory tools.

Question 8

The automation system loses communication between PLC master and slave I/O on Profinet. Some stations show "Station not reachable". How would you troubleshoot?

Accepted Answer

Determine scope (topology) -> Physical checks (cable, switch, slave power) -> Configuration (IP conflict, device name, firmware) -> Diagnostics (TIA Portal, Proneta, ping) -> EMI/noise. Profinet is the most common standard at Siemens-based factories. Proneta (free tool) for network scanning. EMI from VFDs is often overlooked.

Question 9

Factory suddenly loses grid power. UPS maintains servers for 15 minutes. Diesel generator needs 30 seconds to start. How would you handle this?

Accepted Answer

First 30 seconds: ATS auto-transfers -> Check emergency systems (lighting, fire) -> Assess line (restart sequencing) -> Contact EVN -> Load management -> When power returns: verify V/Hz before transfer back. Power loss is the most critical incident. Know ATS, load shedding, generator capacity. Semiconductor factories: 1 second outage can cost millions.

Question 10

You need to maintain a live 380V panel. Describe the complete electrical safety procedure from preparation to re-energizing.

Accepted Answer

Work permit -> LOTO (de-energize -> lock -> tag -> prove-test-prove) -> Temporary grounding -> PPE (insulating gloves, arc flash rated) -> Perform work -> Remove lock/tag in order -> Re-energize -> Logbook. Electrical safety is the ABSOLUTE priority. Prove-test-prove is the gold standard. FDI factories follow NFPA 70E for arc flash. Missing LOTO can get you eliminated.

Question 11

Compare TIA Portal (Siemens) with Studio 5000 (Rockwell) for PLC programming. Do you have experience with EPLAN or AutoCAD Electrical?

Accepted Answer

TIA Portal: all-in-one (PLC+HMI+Drive+Safety), S7-1500 -> Studio 5000: tag-based, CompactLogix -> EPLAN: industry standard for schematics -> AutoCAD Electrical: easier learning curve. TIA Portal dominates in VN due to Siemens prevalence. Studio 5000 needed for American factories. EPLAN is standard at major panel builders. Prepare demos/screenshots.

Question 12

When would you use an oscilloscope, power analyzer, and thermal camera in factory electrical inspection?

Accepted Answer

Oscilloscope: waveform analysis, debug signals, check VFD PWM -> Power analyzer: PF, THD, energy audit -> Thermal camera: loose connections, phase imbalance, panel PM -> Megger: insulation. Thermal cameras are increasingly popular for predictive maintenance. Power analyzers are key for energy audits. Reading oscilloscope waveforms distinguishes junior from mid/senior.

Question 13

Factory has an old relay/contactor-controlled line, frequently breaking. Management wants PLC + HMI upgrade. How would you plan the retrofit?

Accepted Answer

Site survey (I/O, schematics, control sequence) -> Technical proposal (PLC, HMI, protocol) -> Design (EPLAN, programming, HMI) -> Budget & timeline -> Installation (I/O test, dry run, wet run) -> Training -> Handover. Retrofit is common at VN factories transitioning to Industry 4.0. Emphasize risk management (minimal downtime, fallback). Cost: 200M-1B VND. FAT/SAT are key milestones.

Question 14

Vietnam's electrical and automation industry is booming with semiconductors, renewables, and EVs. What is your 3-5 year career plan?

Accepted Answer

Specific passion -> Trend assessment (semiconductor, renewables, VinFast) -> Development plan (certifications) -> Position goals. Interviewers want to know if you

Question 15

What is your expected salary for this electrical/automation engineer position?

Accepted Answer

State range -> Basis (experience, PLC brands, certifications) -> Total compensation (night shift, hazard allowance) -> Flexibility. Vietnam Electrical salary (gross, Aug 2026): Fresher 7-15M, Junior 10-22M, Mid 15-35M, Senior 20-50M (semiconductor: 35-50M). Dual Siemens+AB commands premium. (Data as of Aug 2026. Verify latest)

Question 16

Do you have any questions about this position, the factory electrical/automation systems, or the company?

Accepted Answer

Ask 2-3 questions: (1) PLC brand and SCADA platform? (2) Total electrical capacity? (3) Industry 4.0 plans? Asking about PLC/SCADA shows you want to know your technology stack. On-call duty questions are practical since electrical engineers often work 24/7 shifts.