At Tesco Controls, a Software Engineer plays a vital role in designing, developing, and deploying the mission-critical systems that keep public infrastructure running safely. Unlike traditional software roles focused solely on web applications or SaaS products, software engineering at Tesco Controls sits at the intersection of software development, industrial automation, and electrical engineering. You will write the control logic, configure the SCADA (Supervisory Control and Data Acquisition) systems, and design the human-machine interfaces (HMIs) that monitor and manage water treatment plants, transportation networks, and environmental systems. Your work directly impacts millions of people by ensuring clean water delivery, reliable wastewater treatment, and efficient public utilities. The role is intellectually stimulating and highly collaborative, requiring you to bridge the gap between digital code and physical hardware. You will frequently interact with electrical engineers, project managers, and field technicians to test your software in a physical shop environment before deploying it to real-world municipal facilities. This position requires a unique blend of analytical thinking, systems design, and physical-world problem-solving. Candidates who succeed in this role enjoy seeing their code have a tangible, physical impact on the environment and society.
Phone Screen
reportedInitial phone screen with a recruiter to discuss your background, career goals, and basic alignment with the role.
What to demonstrate
- Initial phone screen with a recruiter to discuss your background, career goals, and basic alignment with the role
- Depth in Automation / automated process control
How to prepare
- Be able to walk your CV end to end in two minutes, and say why this company specifically.
- Have your salary expectations, notice period and location constraints ready, and ask for the rest of the loop in writing.
Semi-Technical Conversation
reportedDiscussion with the hiring manager to dive deeper into your experience with control systems and software engineering.
What to demonstrate
- Discussion with the hiring manager to dive deeper into your experience with control systems and software engineering
- Depth in Automation / automated process control
How to prepare
- Answer aloud and timed: What is latching logic, and why is it important in motor control circuits?
- Answer aloud and timed: How do you handle communication failures between a PLC (Programmable Logic Controller) and a SCADA system?
Onsite Panel Interview
reportedImmersive onsite visit including a presentation, office tour, panel interview with team members, and a written test.
What to demonstrate
- Immersive onsite visit including a presentation, office tour, panel interview with team members, and a written test
- Depth in Automation / automated process control
How to prepare
- Answer aloud and timed: Describe your experience with HMI design and how you ensure an operator can easily understand system states.
- Answer aloud and timed: Explain the difference between AC and DC power and how they are typically used in a control panel.
PracHub editorial advice for the preparation topics above.
Show an interest in the physical hardware
During your shop tour, show genuine curiosity about how the control panels are assembled and wired. Ask questions about the components, the assembly process, and how the software team collaborates with the shop technicians.
Emphasize a safety-first mindset
Because Tesco Controls designs systems for critical infrastructure, safety and reliability are paramount. When answering technical or situational questions, always highlight how your design choices or troubleshooting steps prioritize operator safety and system uptime.
Do not dismiss the basic electrical concepts
Even if your background is purely in Computer Science, failing to demonstrate basic electrical literacy (like understanding how a switch or relay works) can be a red flag for a systems integration company.
Choose a category, try a prompt, then open its approach, worked solution or follow-up when you need it.
Track a rolling failure rate per destination for circuit decisions
The egress service delivers about 1,500 webhooks per second across roughly 40,000 destinations, each call bounded by a 10 second timeout. Maintain, per destination, the failure rate over the trailing 60 seconds so a caller can ask before dispatch whether the circuit should open. Attempts arrive as (destination_id, finished_at_ms, outcome). Requirement: amortised O(1) per attempt, with total memory bounded by the destination count rather than by traffic. Give the structure, its exact memory, and the rule that stops a destination with three attempts from opening a circuit.
Approach
- Name the exact-deque version and then reject it as the default. Holding timestamps and advancing a tail pointer past anything older than now minus 60 seconds is a correct two-pointer window at amortised O(1) per attempt, but its memory tracks in-window traffic, so one destination in a retry storm holds hundreds of thousands of entries while thousands of quiet destinations hold none.
- Use a ring of 60 one-second buckets per destination, each bucket a pair of counters for attempts and failures. On an attempt, advance the ring by the elapsed whole seconds, zeroing at most min(elapsed, 60) buckets, then increment the head. That is amortised O(1) with a fixed footprint per destination.
- State the footprint: 60 buckets times two 4-byte counters is 480 bytes of payload per destination, so 40,000 destinations is roughly 20 to 25 MB with per-entry overhead, bounded by the catalogue rather than by the rate. The cost is granularity, since the oldest bucket ages out in whole seconds, which is far tighter than the decision needs.
- Require a minimum sample before the circuit may open. A destination with three attempts and three failures reads as 100 percent and is not evidence; a floor of roughly 20 attempts in the window makes the ratio meaningful, and below that floor use a run of consecutive failures as the trigger instead.
Follow-up
- The fleet is 30 instances and each sees roughly a thirtieth of a destination's traffic. Where does the rate actually live, and what does a per-instance answer get wrong?
- A destination answers in 9.5 seconds and succeeds. It is not failing but it is consuming your per-destination concurrency. What signal should open the circuit here?
Identify the heaviest tenants in a five-minute window under memory pressure
The edge service handles about 3,000 requests per second across roughly 50,000 tenants, peaking near 9,000. Expose the 50 heaviest tenants by request count over the trailing five minutes so limits can be tightened before one tenant's backfill starves the fleet. You may not retain five minutes of raw records. Give the exact solution and its memory, then the bounded-memory approximation with its error stated as a formula, and say which you would ship and at what tenant cardinality that choice changes.
Approach
- Do the exact version first, because it is affordable at this cardinality: a ring of 300 one-second counters per tenant, advanced lazily, is 1,200 bytes of counters per tenant and roughly 60 to 90 MB for 50,000 tenants with overhead. Carry a running total and subtract the bucket you overwrite so a window read is O(1) rather than 300 adds.
- Extract the top 50 with a size-k min-heap over the tenant sums: O(d log k) for d tenants, against O(d log d) to sort them all. Maintaining the heap continuously instead of on query requires a tenant-to-heap-index map, because incrementing a count already inside the heap means sifting from a known position, and without that map you rebuild the heap on every request.
- State the approximation precisely rather than gesturing at sketches. Misra-Gries with m counters retains every item whose true count exceeds N/(m+1), and each retained count underestimates the truth by at most N/(m+1). With m = 1,000 and N = 900,000 requests in the window the error is roughly 900 requests, which is fine for spotting a tenant sending 50,000 and useless for ranking two tenants 200 apart.
- Say what breaks when the window slides: Misra-Gries and Space-Saving are insert-only and cannot be decremented as records age out. The workable construction is one summary per sub-window, say ten seconds, with 30 summaries merged at query time, and the merged error is the sum of the per-summary errors, so the bound degrades linearly in the number of sub-windows.
Follow-up
- The heaviest tenant is heavy because of one export job rather than user traffic. Should the limiter treat those as the same tenant?
- Two tenants sit tied at the boundary of the top 50. Does your answer flap, and does the flapping matter?
Archive a resource graph without breaking live references or recursing
Resources reference other resources within a tenant; for the largest tenant the reference table holds up to 2,000,000 nodes and 8,000,000 edges. Archiving a resource must archive everything reachable from it that nothing outside the set still references, refuse when a live external referrer exists, and terminate when references form cycles, which they legitimately do. Produce the archive order and the refusal list, targeting O(V+E). Say what stops the traversal crossing a tenant boundary, and why recursion is the wrong control structure at this size.
Approach
- Load the subgraph with the tenant predicate on both endpoints of the edge, not only on the side you started from. Scoping the left table alone is the classic cross-tenant leak: one mis-entered edge then pulls another tenant's resources into the traversal and, worse, into the archive.
- Traverse iteratively with an explicit stack. A 2,000,000-node graph can hold a chain deep enough to exhaust a native stack in the low tens of thousands of frames, and that failure is a process crash rather than an error you can return.
- Treat cycles as data rather than corruption: compute strongly connected components with Tarjan in O(V+E) using its own explicit stack, then condense. The condensation is a DAG, so a topological order over it gives the archive order, and every member of a component archives in one transaction because no order within a cycle is valid.
- Decide refusals with reverse edges. A candidate is archivable only if every in-edge originates inside the candidate set, so build the transpose or count in-degrees restricted to the visited set, and emit each blocked resource with the id of the external referrer, which is the only part of the answer an operator can act on.
Follow-up
- The graph is read in one query and the archive writes a minute later. What can change in between, and how do you make the write safe?
- The candidate set is 400,000 resources. Is that one transaction, and if not, what does a half-finished archive look like to a reader?
Explain why the owner filter ignores the listing index
The only index on resource is (tenant_id, status, updated_at DESC, resource_id DESC). A new endpoint returns one user's resources across all statuses, newest created first: WHERE tenant_id = $1 AND owner_user_id = $2 ORDER BY created_at DESC LIMIT 20. On a tenant with 2M rows it takes 900 ms and EXPLAIN shows a sort above a large scan. Explain precisely why the existing index cannot serve it, give the index that can, and state which of these the new index still will not help: owner_user_id alone across tenants; the same query ordered by updated_at. PostgreSQL 16.
Approach
- Separate the two jobs an index does. For filtering, a composite btree is seekable only on a left prefix, so with no predicate on status the scan can at best range over tenant_id and test owner_user_id per row; PostgreSQL 16 has no btree skip scan to jump the unconstrained column.
- For ordering, the index is sorted by (status, updated_at) within a tenant and not by created_at, so the LIMIT cannot stop early: every matching row is read and then sorted. That is the 'Sort Method: top-N heapsort' line, and it is why the plan reads 2M rows to answer with 20.
- Derive the replacement from the access path — equality, equality, then the ordering column: CREATE INDEX CONCURRENTLY ON resource (tenant_id, owner_user_id, created_at DESC). The scan seeks to the (tenant, owner) range and walks 20 entries in order, so the Sort node disappears along with the row-read.
- Treat INCLUDE (title, status) as conditional, not free. An index-only scan still visits the heap for any row whose page is not marked all-visible, so on a table taking 1.2k writes/second the win depends on autovacuum keeping the visibility map current, and the wider index costs more on every insert.
Follow-up
- 90% of rows are status='active'. Would a partial index WHERE status = 'active' change your answer, and for which of the three queries?
- A dashboard runs this for 40 owners in one page load. What changes about the design?
Stop tag and share joins from fanning out a page
resource_tag is (resource_id, tag_id) with PK (resource_id, tag_id); resource_share is (resource_id, shared_with_user_id, permission). The tagged-and-shared listing inner-joins resource to both, filters tenant_id, tag_id = ANY($2) and shared_with_user_id = $3, orders by updated_at DESC and takes 50. Pages come back with fewer than 50 distinct resources and the total in the header is far too high. Explain the row multiplication, rewrite both the page query and the count query so each is correct, and name the index each one needs. PostgreSQL 16.
Approach
- Do the arithmetic against the predicates that are actually there. An inner join emits one row per matching child row, and both joins are filtered: tag_id = ANY($2) admits only the requested tags, shared_with_user_id = $3 admits one user's share rows. So a resource holding three of the requested tags and shared with $3 once yields three rows, not one — the multiplier is its count of matching tags times its share rows for that single user, and that second factor is 1 unless the table admits duplicate (resource_id, shared_with_user_id) pairs. LIMIT 50 then limits rows rather than resources, and COUNT(*) counts pairs — the header is the product, not the population.
- Reject DISTINCT as the fix. It deduplicates after the product has been built, so the planner must materialise and sort the fanned-out set before the LIMIT can apply, and it leaves any SUM or AVG in the same select list wrong.
- Rewrite both filters as semi-joins, keeping resource as the only row source: AND EXISTS (SELECT 1 FROM resource_tag rt WHERE rt.resource_id = r.resource_id AND rt.tag_id = ANY($2)) and the same shape against resource_share. A semi-join stops at the first match per resource and preserves the driving index order, so ORDER BY updated_at DESC, resource_id DESC LIMIT 50 still stops after 50 rows.
- Count with the same predicates and no join at all: SELECT count(*) FROM resource r WHERE r.tenant_id = $1 AND r.status = 'active' AND EXISTS (...) AND EXISTS (...). Nothing multiplies a resource, so the number is the population.
Follow-up
- The filter changes from 'any of these tags' to 'all of these tags'. Rewrite it and state what it costs relative to the ANY form.
- A resource can be shared with the same user twice under different permissions. Does your count change, and should it?
How do you design the control logic to run and stop a pump safely in an automated process?
How do you design the control logic to run and stop a pump safely in an automated process?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
Explain the concept of feedback loops and how you would use them to maintain a specific water level in a tank.
Explain the concept of feedback loops and how you would use them to maintain a specific water level in a tank.
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
What is latching logic, and why is it important in motor control circuits?
What is latching logic, and why is it important in motor control circuits?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
Explain the difference between AC and DC power and how they are typically used in a control panel.
Explain the difference between AC and DC power and how they are typically used in a control panel.
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
What are the primary differences between Modbus, Ethernet/IP, and Profibus protocols?
What are the primary differences between Modbus, Ethernet/IP, and Profibus protocols?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
Describe how you would set up a basic IP addressing scheme for a small localized control network.
Describe how you would set up a basic IP addressing scheme for a small localized control network.
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
What is the purpose of a relay, and how does it differ from a solenoid?
What is the purpose of a relay, and how does it differ from a solenoid?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
How would you troubleshoot a digital input channel that is not receiving a signal from a field sensor?
How would you troubleshoot a digital input channel that is not receiving a signal from a field sensor?
Approach
- Establish what changed and when, before forming any theory.
- Pick a bisection that eliminates candidates whichever way it turns out.
- Check the instrumentation before believing the symptom.
- Separate the trigger from the cause; the deploy is rarely the bug.
Follow-up
- What would you look at first, and what would it rule out?
- How would you tell a cause from a coincidence here?
Built from the rounds and topics Tesco Controls candidates report.
Prepare, practise & reflect
One practical outcome each day. Spend longer where you need it.
0 / 7 done01Map the Tesco Controls loop
- Write out the reported sequence: Phone Screen, Semi-Technical Conversation, Onsite Panel Interview.
- For each round, write one sentence on what it is judging, from the description above, and mark the one you are least ready for.
Deliverable: A one-page map of the 3 reported rounds, with the weakest marked.
02Work Automation / automated process control
- Spend the session on Automation / automated process control, which Tesco Controls candidates report being tested on.
- Write one worked example in Automation / automated process control and time yourself on it.
Deliverable: One timed worked example in Automation / automated process control.
03Work Control systems concepts
- Spend the session on Control systems concepts, which Tesco Controls candidates report being tested on.
- Write one worked example in Control systems concepts and time yourself on it.
Deliverable: One timed worked example in Control systems concepts.
04Work Pump control / industrial equipment control
- Spend the session on Pump control / industrial equipment control, which Tesco Controls candidates report being tested on.
- Write one worked example in Pump control / industrial equipment control and time yourself on it.
Deliverable: One timed worked example in Pump control / industrial equipment control.
05Answer out loud: Control Systems & Automation Logic
- Answer aloud, timed: How do you design the control logic to run and stop a pump safely in an automated process?
- Answer aloud, timed: Explain the concept of feedback loops and how you would use them to maintain a specific water level in a tank.
Deliverable: Spoken answers to 2 reported Control Systems & Automation Logic question(s), under time.
06Answer out loud: Basic Electrical & Networking
- Answer aloud, timed: Explain the difference between AC and DC power and how they are typically used in a control panel.
- Answer aloud, timed: How would you troubleshoot a digital input channel that is not receiving a signal from a field sensor?
Deliverable: Spoken answers to 2 reported Basic Electrical & Networking question(s), under time.
07Answer out loud: Behavioral & Collaboration
- Answer aloud, timed: Describe a time when you had to work with a multidisciplinary team (e.g., electrical engineers, project managers) to solve a tough technical problem.
- Answer aloud, timed: How do you handle situations where the project requirements are ambiguous or change mid-development?
Deliverable: Spoken answers to 2 reported Behavioral & Collaboration question(s), under time.
Expand any day for tasks and deliverables. Your progress is saved on this device.
Behavioural rounds judge the decision you made and what it cost.
How do you handle communication failures between a PLC (Programmable Logic Controller) and a SCADA system?
How do you handle communication failures between a PLC (Programmable Logic Controller) and a SCADA system?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
Describe your experience with HMI design and how you ensure an operator can easily understand system states.
Describe your experience with HMI design and how you ensure an operator can easily understand system states.
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
Describe a time when you had to work with a multidisciplinary team (e.g., electrical engineers, project manage
Describe a time when you had to work with a multidisciplinary team (e.g., electrical engineers, project managers) to solve a tough technical problem.
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
How do you handle situations where the project requirements are ambiguous or change mid-development?
How do you handle situations where the project requirements are ambiguous or change mid-development?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
Tell me about a time you made a mistake on a project. How did you identify it, and what did you do to resolve
Tell me about a time you made a mistake on a project. How did you identify it, and what did you do to resolve it?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
How do you manage your workload and prioritize tasks when working on multiple projects simultaneously?
How do you manage your workload and prioritize tasks when working on multiple projects simultaneously?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
Why are you interested in working in the water/wastewater and municipal infrastructure industry?
Why are you interested in working in the water/wastewater and municipal infrastructure industry?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
- 01
How do you handle communication failures between a PLC (Programmable Logic Controller) and a SCADA system?
- 02
Describe your experience with HMI design and how you ensure an operator can easily understand system states.
- 03
Describe a time when you had to work with a multidisciplinary team (e.g., electrical engineers, project managers) to solve a tough technical problem.
- 04
How do you handle situations where the project requirements are ambiguous or change mid-development?
How difficult is the technical written test during the onsite interview?
The test is generally considered average in difficulty. It focuses on fundamental electrical engineering knowledge, such as Ohm's law, identifying components on a basic schematic, and simple logic gates or control concepts. If you have an engineering background or have reviewed basic circuit design, you should feel comfortable.
Tesco Controls Software Engineer candidate reports ↗What is the company culture like at Tesco Controls?
The culture is highly collaborative, supportive, and community-oriented. Candidates frequently highlight the warm, welcoming environment during the onsite interview, the open-door policy of management, and the strong emphasis on teamwork. It is a place where people are genuinely eager to help you succeed.
Tesco Controls Software Engineer candidate reports ↗Do I need prior experience in the water/wastewater industry to apply?
While prior experience in water/wastewater or industrial automation is a tremendous advantage, it is not an absolute requirement. Tesco Controls values strong engineering fundamentals, a willingness to learn, and a solid problem-solving mindset. They are highly willing to train the right candidate who demonstrates curiosity and strong basic skills.
Tesco Controls Software Engineer candidate reports ↗How much travel is required for this Software Engineer role?
Travel requirements can vary depending on the specific team and project phase. Some roles may involve occasional travel to municipal sites for field commissioning, testing, and client meetings, while others are more focused on in-house development and factory testing. It is best to clarify this with the hiring manager during your initial interview.
Tesco Controls Software Engineer candidate reports ↗What topics does Tesco Controls test in interviews?
Tesco Controls interviews most often cover Automation / automated process control, Control systems concepts, Pump control / industrial equipment control, Automated process run/stop state logic, and Electrical knowledge (basic electrical theory). The exact emphasis depends on the specific role you apply for.
Tesco Controls Software Engineer candidate reports ↗Sources & methodology 3 sources ↗
No official company page is cited. Rounds and questions come from candidate reports and PracHub editorial material; each source shows the date it was read.
- 01Tesco Controls Software Engineer candidate reports ↗
Company-reported rounds, questions and FAQ.
Candidate reports · Accessed 2026-09-22 - 02PracHub Software Engineer practice ↗
PracHub practice material, not company-reported.
PracHub page · Accessed 2026-09-22 - 03PracHub preparation framework ↗
PracHub preparation guidance.
PracHub page · Accessed 2026-09-22
Explore related engineering environments and compare the preparation focus.
Vercel Software Engineer Interview Guide
Debugging practice for Vercel software engineer prep built on a reproduction you trust, narrowing to the smallest failing input, and changing one variable per run so the result stays attributable.
Together Ai Software Engineer Interview Guide
Failure-handling practice for Together Ai software engineer candidates: requests whose outcome a timeout leaves unknown, where a retry is safe, and deduplicating at the receiver instead of assuming exactly-once delivery.
Lambda Software Engineer Interview Guide
Failure-handling practice for Lambda software engineer candidates: requests whose outcome a timeout leaves unknown, where a retry is safe, and deduplicating at the receiver instead of assuming exactly-once delivery.
CoreWeave Software Engineer Interview Guide
Failure-handling practice for CoreWeave software engineer candidates: requests whose outcome a timeout leaves unknown, where a retry is safe, and deduplicating at the receiver instead of assuming exactly-once delivery.