Electrical Design Engineer Interview Questions UK: 8 Real Questions and What Interviewers Want

Before your Electrical Design Engineer interview, it helps to see the questions from the interviewer's side. We have picked eight from our set of 16 and added the reason each one gets asked.

Eight Electrical Design Engineer interview questions, and what the interviewer is thinking

1. How do you size a cable for a new circuit under BS 7671?

Why they ask: Cable selection is the most fundamental calculation an electrical design engineer does.

2. Explain how you would carry out a fault level study and why it matters for equipment selection.

Why they ask: Fault levels dictate switchgear and protection ratings, and errors are dangerous.

3. How do you achieve discrimination between protective devices, and what do you do if you cannot?

Why they ask: Selectivity affects reliability, so designers must be able to coordinate protection.

4. What are the key requirements for earthing and bonding in a design, and how do the different earthing systems affect it?

Why they ask: Earthing is essential for safety and an area where design errors cause serious harm.

5. Which design software have you used, and how do you ensure your drawings and schematics are accurate and well coordinated?

Why they ask: They want to know your tool experience and quality control habits.

6. You discover a cable sizing error in a design that has already been issued to the contractor, and cables are on order. What do you do?

Why they ask: They are testing honesty, urgency and practical error management.

7. Tell me about a time you solved a difficult design problem on an electrical project.

Why they ask: They want to see problem-solving depth in a real design context.

8. Why did you choose electrical design engineering, and what do you find most rewarding about it?

Why they ask: They want to understand genuine interest and fit.

A sample answer to question 1

How do you size a cable for a new circuit under BS 7671?

Cable sizing begins with the design current, taken from the load and any diversity applied. I choose the protective device rating to be at least that value, then select a cable whose current-carrying capacity, after applying correction factors, is not less than the device rating. Those factors cover ambient temperature, grouping of circuits, thermal insulation and the installation method from Appendix 4 of BS 7671. Next I check voltage drop against the limits, normally 3 per cent for lighting and 5 per cent for other uses on a low-voltage installation, using the mV/A/m values. Then I verify that the protective device will disconnect within the required time under fault conditions by checking earth fault loop impedance, and that the cable can withstand the prospective fault energy using the adiabatic equation, k squared S squared. If any check fails I increase the conductor size or change the protection. I record the calculations in design software such as Amtech or a validated spreadsheet.

Common mistake to avoid: Skipping the fault protection check; forgetting grouping and ambient factors

Want the rest?

Full model answers, key points and common mistakes for all 16 questions are on the Electrical Design Engineer interview questions page. The first five are free, no sign-up needed.