Electrical Engineer interview questions and answers

"How would you size the supply for a new building?"

Describe the sequence. Collect the connected loads by category: lighting, small power, air conditioning, lifts, pumps, kitchen and any special equipment. Apply demand and diversity factors, because not everything runs at once. Add a margin for known future load, then convert to kVA at the expected power factor to size the transformer and main switchgear.

Say what you would check afterwards: the fault level the transformer implies, whether the utility can supply at that point, and whether standby generation or uninterruptible supply is needed for particular loads.

"Explain discrimination between protective devices."

Discrimination, or selectivity, means the device nearest a fault operates and the ones upstream do not, so a single fault does not black out the building. Achieving it means grading time and current characteristics: ratings that step up toward the source, and where curves overlap, time delays or devices designed for selectivity.

Add that discrimination is verified against the fault levels at each point, not assumed from ratings alone, and that it is a common finding in inspection reports because it is easy to get wrong when an installation is extended.

"A cable you specified is running warm. What do you do?"

Start with measurement rather than replacement. Check the actual load current against the design current, look for loads added since the design, and check the installation conditions: grouping, insulation, ambient temperature and how the cable is supported. Compare what is on site with what the design assumed, because the difference is usually the answer.

Then act in order: relieve the overload if there is one, confirm the protective device is correct, and if the cable is genuinely undersized for its conditions, plan a replacement rather than accepting it. Explain that you would record what changed and why.

"How do you make sure a design is buildable and maintainable?"

Talk about the practical side of design: access for maintenance, space for cable bending radii and future circuits, and labelling. Mention isolation points that allow part of the installation to be worked on while the rest runs, and equipment that can be obtained locally with spares. Say that you review designs with the people who will install and maintain them, because they see problems drawings hide.

"Tell us about a design decision you got wrong."

Give a real example, including the consequence and what it cost in time or money. Explain how it was found, how you corrected it, and what you changed in your method: a checklist item, a calculation you now always verify, or a review step you added. Engineers who claim never to have been wrong worry panels more than those who learn systematically.

"How do you work with contractors on site?"

Describe clear expectations and evidence: approved drawings and specifications, agreed inspection points, witnessing the tests that matter, and written instructions for changes rather than verbal ones. Say that you look for problems early, when they are cheap to fix, and that respect for the people doing the work gets better results than policing them.

"What is your responsibility for safety as a designer?"

Explain that design decisions shape risk long before anyone switches on: protection that disconnects in time, earthing that works, equipment rated for the fault level, adequate isolation, and arrangements that let maintenance happen safely. Add that you flag residual risks to the client and the contractor rather than assuming someone will notice them.