SSE · Software Engineer
Updated · 2026-10-02

SSE Software Engineer
Interview Guide

THE 60-SECOND BRIEF

At SSE, the Software Engineer role is not a traditional IT position. It is a critical engineering function embedded within the core of the energy sector. You will be responsible for designing, maintaining, and optimizing the complex control and operational systems that keep essential infrastructure running. This role bridges the gap between software logic and physical electrical grids, playing a vital part in the transition to a net-zero future. Your work will directly impact the reliability and efficiency of energy distribution. Whether you are working on OT (Operational Technology) systems, Control Systems, or Power System Engineering, your code and logic directly influence how power is managed across Scotland and beyond. This is a role for engineers who thrive on high-stakes environments where precision, safety, and system stability are the primary measures of success.

This guide is scoped to a Software Engineer candidate at SSE.

No round sequence has been reported for SSE. Confirm the format with your recruiter.

Technical and Domain ExpertiseTechnical Rigor and System ReliabilityRole Requirements & Qualifications

24 min read

Browse Software Engineer questions

See the practice prompts

22Practice promptsAcross five skill areas

At SSE, the Software Engineer role is not a traditional IT position. It is a critical engineering function embedded within the core of the energy sector. You will be responsible for designing, maintaining, and optimizing the complex control and operational systems that keep essential infrastructure running. This role bridges the gap between software logic and physical electrical grids, playing a vital part in the transition to a net-zero future. Your work will directly impact the reliability and efficiency of energy distribution. Whether you are working on OT (Operational Technology) systems, Control Systems, or Power System Engineering, your code and logic directly influence how power is managed across Scotland and beyond. This is a role for engineers who thrive on high-stakes environments where precision, safety, and system stability are the primary measures of success.

01

Preparation focus

editorial

No round sequence has been reported for this company, so confirm the format with your recruiter and work the reported questions below.

What to demonstrate

  • Breadth across the topics this company reports testing
  • Whether you confirm the format before preparing for it

How to prepare

  • Ask the recruiter for the sequence, the duration of each stage and whether you will be writing code
  • Work the reported questions below and time yourself
PracHub preparation framework ↗

PracHub editorial advice for the preparation topics above.

01

Focus on the "Why

When discussing past projects, explain the business or safety impact of your decisions.

02

Safety First

Always mention how you accounted for safety and risk mitigation in your technical answers.

03

Know your stack

Research the specific tools or protocols (like SCADA or specific PLC logic) used by the team you are interviewing with.

Choose a category, try a prompt, then open its approach, worked solution or follow-up when you need it.

19 technical prompts0 include a worked solution

Diff a projection against the primary without per-row point reads

hard
reconciliationrange hashingthrottling

The listing projection has drifted and some rows show a stale version. The primary holds 40,000,000 resource rows across 12,000 tenants while serving 1,200 writes and 14,000 reads per second. The obvious repair, reading each resource row and comparing its version against the projection, is correct and would eventually finish. Explain precisely why it is unacceptable here, then give a diff that finds the differing rows, state its complexity, and make it safe to run against a live primary. Replication lag is usually under 100 ms and is not bounded.

Approach
  1. Quantify the naive cost rather than calling it slow: 40,000,000 point reads at even 0.5 ms each is over five hours serialised, and the only lever is concurrency, which is exactly what you cannot spend. The primary's pool is sized for the write path, and 40,000,000 random reads evict the buffer cache that sustains the 85 percent cache hit rate, so the audit degrades the system it is auditing.
  2. Replace random access with one ordered pass per side. Both sides can be read in (tenant_id, resource_id) order, which is a sequential scan on each and a merge join in O(n) time and O(1) memory. For a dense diff that is the whole answer, and it reads the primary once instead of 40,000,000 times.
  3. For the expected sparse case, compare range hashes instead of rows: partition the key space, compute per range an order-independent aggregate over hash(resource_id, version), compare aggregates, and descend only into ranges that differ. With d differing rows and branching factor B, at most d ranges mismatch per level, so the drill-down examines O(d log_B(n/d)) ranges and reads full rows only in mismatching leaves.
  4. Aggregate with a sum modulo 2^64 or a multiset hash, never XOR. XOR is order-independent but self-cancelling, so two rows wrong in the same way, or a row duplicated on one side, leave the range aggregate matching and the range is declared clean.
Follow-up
  • The diff reports 900 stale rows. How do you decide between patching those rows and rebuilding the projection from resource_revision?
  • Same job, but the projection lives in a search index that cannot be scanned in key order. What changes?

Identify the heaviest tenants in a five-minute window under memory pressure

medium
top-kheavy hittersstreaming

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
  1. 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.
  2. 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.
  3. 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.
  4. 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

medium
graph traversaltopological ordertenant isolation

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
  1. 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.
  2. 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.
  3. 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.
  4. 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?

Built from the topics and questions SSE candidates report; no round sequence has been reported.

Small steps. Visible outcomes.0 / 7 completed
ONE WEEK · YOUR PACE

Prepare, practise & reflect

One practical outcome each day. Spend longer where you need it.

0 / 7 done
01Establish the SSE format
  • No round sequence has been reported, so ask your recruiter for the sequence, the duration of each stage and whether you will write code.

Deliverable: A written reply from your recruiter confirming the format.

02Answer out loud: Technical and Domain Expertise
  • Answer aloud, timed: Describe your experience with OT (Operational Technology) and how it differs from standard enterprise software.
  • Answer aloud, timed: How do you ensure the stability and safety of a system when deploying updates to critical infrastructure?

Deliverable: Spoken answers to 2 reported Technical and Domain Expertise question(s), under time.

03Answer out loud: Technical Rigor and System Reliability
  • Answer aloud, timed: System lifecycle management – How you design for long-term maintenance and updates.
  • Answer aloud, timed: Fail-safe protocols – Your approach to ensuring systems remain stable during unexpected events.

Deliverable: Spoken answers to 2 reported Technical Rigor and System Reliability question(s), under time.

04Answer out loud: Role Requirements & Qualifications
  • Answer aloud, timed: Must-have skills: Proficient in relevant programming languages for control systems, strong understanding of OT/ICS concepts, and experience with systems engineering principles.
  • Answer aloud, timed: Nice-to-have skills: Familiarity with energy industry regulations, experience with SCADA systems, and a background in electrical or mechanical engineering.

Deliverable: Spoken answers to 2 reported Role Requirements & Qualifications question(s), under time.

05Consolidate
  • Re-work the problem you got wrong earliest in the week, from scratch, without looking at your previous attempt.

Deliverable: A second, cleaner solution to the problem you got wrong first.

06Rehearse your own examples
  • Prepare three examples from your own work where you made the decision, each with the outcome you can quantify.

Deliverable: Three examples written out, each with a number attached.

07Dry run for SSE
  • Run one full mock under time, then write down the two questions you most want to ask your interviewers.

Deliverable: A completed timed mock and two questions to ask.

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.

Describe your experience with OT (Operational Technology) and how it differs from standard enterprise software

medium
Technical and Domain Expertise

Describe your experience with OT (Operational Technology) and how it differs from standard enterprise software.

Approach
  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. 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 callers you do not own that their integration breaks

medium
deprecationcompatibilitystakeholders

A field in a write endpoint's response must change shape. You own the endpoint; you do not own the four internal callers or the outbound webhook consumers who read it. Describe a deprecation you were responsible for: what you shipped first, how you established who was actually reading the field, the window you gave and what set its length, what you did about the consumer who never moved, and how you decided removal was safe. Name the signal you used, not the announcement you sent.

Approach
  1. Establish the reader set empirically rather than from a wiki of owners: per-field usage counters keyed by principal, or access logs attributed to a consumer. State the blind spot of whichever you pick, since a consumer that reads the field only on a monthly job will not appear in a week of logs.
  2. Ship additive first. Populate the new field alongside the old one so no reader is forced to move, which is also what keeps a rolling deploy safe, because old and new instances answer the same requests at the same time and a rollback must still find the old shape present.
  3. Set the window from the slowest legitimate consumer's release cadence, not from your calendar, and decide separately what to do for a consumer with no release process at all, such as an external webhook endpoint you can only email.
  4. Convert silence into evidence before you rely on it: a short, low-traffic removal window that makes a still-dependent consumer fail visibly and loudly while you are watching, rather than at three in the morning after you have moved on.
Follow-up
  • How would you detect a consumer that reads the field only during a monthly export?
  • One caller refuses to move and has a commercial relationship behind it. What changes in your plan and what does not?

Ship under a deadline and bound the debt you chose

medium
paginationtechnical debttradeoffs

You have four days to ship a tenant-facing listing endpoint. The version you would defend uses keyset pagination over (tenant_id, status, updated_at DESC, resource_id DESC); the version you can finish uses LIMIT/OFFSET with no matching index. Describe a deadline call you actually made of this shape: what you shipped, what you knowingly deferred, how you bounded the damage with a mechanism rather than an intention, and the specific numeric condition that would force the follow-up. Name who you told and where you wrote it down.

Approach
  1. Name the deferred failure precisely instead of calling it slow. OFFSET n makes the database produce and discard n rows, so cost grows with page depth; without an index matching the sort, every matching row is read and sorted before the limit applies; and rows inserted between two page fetches shift across the boundary so items are skipped or repeated with nothing in the response to signal it.
  2. Bound the blast radius with something mechanical rather than a promise: cap maximum page depth, cap page size, restrict the endpoint to one internal caller, or keep it behind a flag. State which failure each cap removes and which it leaves standing.
  3. Attach a number to the trigger and wire it to an alarm: the first tenant crossing N resources, or the endpoint's p99 crossing its share of the 400 ms budget, so the debt announces itself instead of waiting to be remembered.
  4. Write it where the next engineer looks, which is the code and the ticket, not a chat message: what was deferred, why, the cap, and the trigger.
Follow-up
  • At what page depth does the offset version breach your latency budget, given your page size and row counts?
  • What breaks first when you switch to keyset pagination later, and what does a client holding an old page token see?
  • 01

    Describe your experience with OT (Operational Technology) and how it differs from standard enterprise software.

  • 02

    A field in a write endpoint's response must change shape. You own the endpoint; you do not own the four internal callers or the outbound webhook consumers who read it. Describe a deprecation you were responsible for: what you shipped first, how you established who was actually reading the field, the window you gave and what set its length, what you did about the consumer who never moved, and how you decided removal was safe. Name the signal you used, not the announcement you sent.

  • 03

    You have four days to ship a tenant-facing listing endpoint. The version you would defend uses keyset pagination over (tenant_id, status, updated_at DESC, resource_id DESC); the version you can finish uses LIMIT/OFFSET with no matching index. Describe a deadline call you actually made of this shape: what you shipped, what you knowingly deferred, how you bounded the damage with a mechanism rather than an intention, and the specific numeric condition that would force the follow-up. Name who you told and where you wrote it down.

PracHub preparation framework ↗
How long should I spend preparing for the technical interview?

Dedicate at least two weeks to reviewing your core technical domain. Focus on the specific systems mentioned in your job description, such as Control Systems or Protection Engineering, rather than general coding challenges.

SSE Software Engineer candidate reports ↗
Is the interview process mostly remote or in-person?

SSE often utilizes a mix of video screens and in-person interviews, particularly for roles located in areas like Inverness, Perth, or Glasgow. Check your specific invitation for location details.

SSE Software Engineer candidate reports ↗
What is the company culture like for engineers?

The culture is professional, safety-conscious, and mission-driven. You will find a team that values collaboration and long-term stability over the "move fast and break things" mentality common in other tech sectors.

SSE Software Engineer candidate reports ↗
What topics does SSE test in interviews?

SSE interviews most often cover Competency-Based Interviewing, Power Systems Engineering, Control Systems Engineering, Systems Engineering, and Project Management. The exact emphasis depends on the specific role you apply for.

SSE 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.