Whether it is a company interview, a vetting check or your oral exam, marine high voltage interview questions separate the candidates who really understand the ship’s electrical plant from those who only memorised definitions. After 15+ years as a Senior ETO on high-voltage ships, here are the questions that come up again and again — with the model answers interviewers and examiners actually want to hear.
Safety questions
How do you make an HV circuit safe to work on?
Permit to work → isolate and rack out the breaker → lock off → prove the voltage detector on a known live source → test dead → prove the detector again → apply earthing → display notices → start work. Earthing after isolation discharges stored charge and holds the circuit at earth potential.
What are the dangers of HV compared with LV?
Arc flash and arc blast, flashover across an air gap without contact, stored capacitive charge, induced voltage and step/touch potential. With HV you can be injured without ever touching the conductor — which is why approach distance and PPE matter.
Systems questions
Why is HV used on ships and at what voltages?
For large loads, higher voltage means lower current for the same power, so smaller cables, less weight and lower losses. Typical marine HV: 3.3 kV, 6.6 kV and 11 kV.
Why is the HV neutral high-resistance earthed?
A resistor in the neutral limits earth-fault current so the first earth fault alarms but does not trip the ship. The vessel keeps running while you locate the fault, and transient overvoltages are limited.
What interlocks protect HV switchgear?
You cannot rack a closed breaker, the earth switch cannot close on a live circuit, and the panel will not open unless the circuit is isolated and earthed. They enforce the correct sequence — never defeat one.
Maintenance questions
How do you test an HV motor’s insulation resistance?
Isolate, discharge and earth first; use a 5 kV insulation tester; take 1- and 10-minute readings for the Polarization Index (PI ≥ 2 is healthy); discharge the winding afterwards. We cover this in detail in our guide to insulation resistance testing on ships.
Preparing for the oral? See the full breakdown of ETO oral exam questions on high voltage, and grab the free practice set below.
Disclaimer: For exam preparation and revision only. Not a certified STCW course.