Overheating Transformers & Switchgear Failures – Who Is Liable? (UK Guide)

Introduction

When a transformer or a piece of switchgear overheats, the damage can spread fast: smoke and fire risk, power loss, damaged plant, spoiled stock, and business interruption. The big question that follows is usually the same: who is liable? In the UK, liability depends on who owned the equipment, who controlled it day-to-day, what maintenance was required, and whether anyone breached a duty of care.

This article explains the most common liability routes after overheating failures in transformers, LV/HV switchgear, busbars, and associated protection equipment. It’s written for property owners, facilities managers, manufacturers, and contractors who need a clear view of risk, evidence, and insurance.

Common causes of overheating (and why they matter for liability)

Overheating is rarely “bad luck”. The cause often points directly to the responsible party.

• Loose connections and high resistance joints (e.g., lugs, terminations, busbar joints)
• Overloading (increased demand, new machinery, EV chargers, HVAC upgrades)
• Poor ventilation or blocked airflow in substations/switch rooms
• Ageing insulation and partial discharge leading to progressive failure
• Protection settings issues (incorrect relay settings, coordination failures)
• Contamination and moisture ingress (dust, salt air, water leaks)
• Harmonics and power quality problems from non-linear loads
• Poor workmanship during installation, modification, or repairs
• Manufacturing defects (materials, design, assembly)

A good investigation will link the failure mode to a controllable factor: maintenance, design, installation, operation, or environment.

Liability basics in the UK: duty, breach, causation, loss

Most liability disputes come down to four questions:

1. Who owed a duty of care? (owner, occupier, contractor, manufacturer, etc.)
2. Was there a breach? (poor maintenance, unsafe work, defective product)
3. Did the breach cause the failure and loss? (not just “it happened”)
4. What losses are recoverable? (property damage, business interruption, third-party losses)

Contracts also matter. A party may accept responsibility in a lease, service agreement, or works contract even if they didn’t “cause” the problem in a practical sense.

Who could be liable? The usual suspects

1) The building owner or landlord

If the transformer/switchgear is part of the building’s electrical infrastructure, the landlord often has obligations to keep it safe and maintained—especially in multi-let buildings.

Landlord liability is more likely where:

• The lease makes the landlord responsible for base build electrical systems
• The landlord controls access to the substation/switch room
• Maintenance is arranged centrally (via managing agent)
• Known issues were not addressed (hot spots, nuisance trips, ageing kit)

Even where a tenant operates equipment day-to-day, a landlord may still be liable if they retained control or failed to manage foreseeable risks.

2) The tenant or occupier

Tenants can be liable where they:

• Overload the system by adding equipment without assessing capacity
• Block ventilation, store items in electrical rooms, or restrict access
• Ignore warning signs (burning smell, discolouration, repeated trips)
• Fail to maintain tenant-owned distribution boards, MCCs, or local switchgear

In practice, liability often turns on the lease: who is responsible for “plant and machinery”, who must maintain, and who must not alter without consent.

3) Facilities management (FM) provider or maintenance contractor

Maintenance contractors can be liable if they:

• Miss obvious defects during inspections
• Fail to torque/secure terminations correctly
• Use incorrect parts or poor-quality consumables
• Don’t follow manufacturer guidance or safe systems of work
• Fail to recommend urgent remedial works (or fail to document it)

A key point: liability isn’t only about what was done—it’s also about what should have been flagged. If a contractor’s reports repeatedly say “satisfactory” while evidence shows progressive overheating, that can become central.

4) Electrical installation contractor (design and build / project works)

If the overheating follows recent works—panel replacement, load upgrades, generator/UPS installation, EV charging, PV, or a change in protection settings—then the installing contractor may be in the frame.

Common allegations include:

• Wrong cable sizing or inadequate derating
• Poor termination practices
• Incorrect protection coordination
• Failure to commission properly
• Failure to test under load or record baseline thermal readings

5) The manufacturer (product liability)

Manufacturers may be liable where a defect in design, materials, or manufacturing caused the failure. This can include:

• Inadequate creepage/clearance distances
• Defective insulation systems
• Poor-quality contacts leading to overheating
• Inadequate thermal design or rating claims

Product liability claims are evidence-heavy. Preserving failed components and maintaining a clear chain of custody is crucial.

6) The Distribution Network Operator (DNO) or IDNO

If the transformer is on the network side, ownership may sit with the DNO/IDNO. Liability can arise where:

• Network equipment was defective or poorly maintained
• There was a failure to manage known risks
• Outages or faults were caused by network-side issues

However, DNO responsibilities and limitations can be complex, and some losses may be excluded or capped depending on the circumstances and agreements.

7) Designers, consultants, and dutyholders

Where a consultant specified the equipment or protection scheme, or where dutyholders under CDM had responsibilities, liability can extend to:

• Poor design decisions
• Inadequate risk assessment
• Failure to coordinate interfaces between systems

Shared liability: it’s often not “one party”

Overheating failures frequently involve multiple contributing factors: ageing kit, increased load, marginal ventilation, and a loose termination after a minor modification. In those cases, liability may be split.

From a practical standpoint, that means:

• Multiple insurers may be involved
• Recovery actions (subrogation) can run in parallel
• Early evidence gathering matters, because parties will defend their position quickly

What evidence typically decides the outcome

If you want a defensible position—whether you’re claiming or defending—focus on evidence that shows control, competence, and causation.

• Ownership and responsibility documents: leases, O&M manuals, adoption agreements
• Maintenance records: planned preventative maintenance (PPM), test certificates, service reports
• Thermal imaging history: IR surveys, hot spot photos, trend reports
• Load studies: maximum demand data, power quality reports, harmonic measurements
• Commissioning records: settings files, protection coordination studies
• Condition monitoring: dissolved gas analysis (DGA) for oil-filled transformers, partial discharge testing
• Incident timeline: alarms, trips, call-outs, temporary repairs
• Photos and component preservation: failed lugs, contacts, busbar joints, insulation

If there’s a fire, the fire investigator’s findings and the electrical engineer’s root cause analysis will carry significant weight.

Regulatory and safety context (why it matters)

While liability is often contractual, safety duties can influence negligence arguments.

Relevant UK frameworks may include:

• Electricity at Work Regulations 1989 (duty to maintain systems to prevent danger)
• Health and Safety at Work etc. Act 1974 (general duties to protect people)
• BS 7671 (wiring regulations) as a benchmark for good practice
• HSE guidance and manufacturer instructions for maintenance and safe access

A failure to follow widely accepted standards can make it harder to defend a claim.

Which insurance policies may respond?

Liability and first-party cover are different. You may have cover for your own losses even if you can’t pin liability on someone else.

Property damage and business interruption

• Commercial property insurance can cover damage to insured property and may include business interruption.
• Machinery breakdown / engineering inspection policies can be relevant for sudden and accidental breakdown of plant, including electrical equipment (cover varies).

Public liability and products liability

• Public liability may respond if third parties suffer property damage or injury due to your negligence (e.g., a tenant’s kit damaged due to landlord-controlled switchgear failure).
• Products liability may respond for manufacturers/suppliers where a defective product causes damage.

Professional indemnity

• Professional indemnity (PI) may respond where the allegation is a professional failing (design error, specification issue, incorrect settings advice), rather than faulty workmanship.

Contractors’ insurance

• Contractors may rely on public liability, contract works, and sometimes Erection All Risks (EAR) depending on the project.

Policy wordings and exclusions matter. Electrical failures can trigger debates around wear and tear, gradual deterioration, defective workmanship, and “resultant damage”.

Practical steps after an overheating incident

How you act in the first 48 hours can affect both liability and insurance.

1. Make safe: isolate power, secure the area, prevent re-energisation.
2. Notify stakeholders: landlord/tenant/FM/DNO as relevant.
3. Preserve evidence: don’t discard failed parts; photograph before disturbance.
4. Document the timeline: alarms, smells, trips, load changes, recent works.
5. Engage competent investigators: electrical engineer, fire investigator if needed.
6. Notify insurers early: property and liability insurers may need prompt notice.
7. Control communications: avoid speculative blame in emails; stick to facts.

How to reduce future liability exposure

Even if you never have a major failure, good controls reduce both risk and disputes.

• Capacity and load management: review maximum demand before adding load
• Routine thermal imaging: trend hot spots, not just one-off surveys
• Torque and termination controls: documented torque settings and QA checks
• Ventilation and housekeeping: keep switch rooms clear and cool
• Protection reviews: settings reviews after any system change
• Clear responsibility mapping: leases and service contracts should state who maintains what

FAQs

Who is responsible for a transformer in a commercial building?

It depends on ownership and the lease. In some sites the transformer is network-owned (DNO/IDNO). In others it’s privately owned and maintained by the landlord or the occupier.

If the tenant overloads the system, is the landlord still liable?

Potentially. If the landlord retained control of the main switchgear and failed to manage capacity, there may be shared liability. Lease terms and evidence of warnings/consent are key.

Can a maintenance contractor be liable if they didn’t cause the fault?

Yes—if they failed to identify and report foreseeable defects, or if their inspection and testing fell below expected standards.

Does insurance cover overheating and electrical failure?

Often, but not always. Property policies may cover resultant damage and business interruption. Engineering/machinery breakdown policies can be relevant. Exclusions for wear and tear or gradual deterioration may apply.

What evidence should we keep?

Keep failed components, photos, maintenance records, thermal imaging reports, load data, and commissioning/protection settings. Chain of custody matters if a dispute is likely.

Conclusion and next step

Overheating transformer and switchgear failures sit at the intersection of engineering, contracts, and insurance. Liability can fall on the party that owned the equipment, controlled the environment, performed the work, or failed to maintain and monitor known risks. The best outcomes come from early evidence preservation, clear documentation, and a structured investigation.

If you want help reviewing your responsibilities, tightening maintenance documentation, or arranging the right mix of property, engineering, and liability cover, speak to a specialist commercial insurance broker who understands electrical plant and complex claims.