PLC Engineer Interview Questions UK: 8 Real Questions and What Interviewers Want

Before your PLC 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 PLC Engineer interview questions, and what the interviewer is thinking

1. What does a PLC engineer do on a typical day, and what made you want to specialise in PLC programming?

Why they ask: To establish whether you understand the practical, site-based nature of the work.

2. Explain the PLC scan cycle and how it affects the way you write your programme.

Why they ask: The scan cycle is fundamental, and misunderstanding it leads to subtle bugs.

3. How do you structure a PLC programme so that it is easy to maintain and reuse?

Why they ask: Code quality is a major differentiator because other engineers will inherit your work.

4. Which PLC platforms have you used, and how do you organise a project in that software, for example in TIA Portal or Studio 5000?

Why they ask: They want to confirm hands-on platform experience and sensible project organisation.

5. How do you scale and handle analogue signals in a PLC, and how do you detect faults such as a broken wire?

Why they ask: Analogue handling is a routine task and failure detection shows a safety-minded approach.

6. How do you design fault handling and restart so a machine recovers safely after an emergency stop or loss of air?

Why they ask: Recovery logic affects safety and productivity, and poor design causes damage or unsafe starts.

7. It is 3am and a call tells you a line has stopped after a power dip and the PLC is in a major fault state. What do you do?

Why they ask: Out-of-hours fault response is common, and they look for calm, safe and systematic action.

8. Tell me about a time you wrote the PLC programme for a new machine from a specification. How did you go about it?

Why they ask: They want to see an end-to-end approach, from specification to proven software.

A sample answer to question 1

What does a PLC engineer do on a typical day, and what made you want to specialise in PLC programming?

My days vary between desk and site. At my desk I write and test logic in the programming software, design HMI screens, review specifications and produce documentation such as I/O lists and functional descriptions. On site I commission machines, test inputs and outputs, tune drives and chase faults with maintenance teams. Sometimes I am called to a stopped line to find out why a sequence is stuck, and a lot of that comes down to reading diagnostics, checking sensors and understanding the programme logic. What attracted me to PLC work is that it is very practical. You write something, then watch a real machine respond, and you quickly learn whether your thinking was right. I like the logic and structure involved, and I enjoy the satisfaction of making a line run reliably after fixing a stubborn fault. It also combines electrical, mechanical and software knowledge, so I never feel that I have finished learning.

Common mistake to avoid: Only describing coding; Not mentioning documentation

Want the rest?

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