This guidance supports electrical thermography practitioners in delivering safe, consistent, and high‑quality electrical thermography surveys.
Training and Pathways
Practitioners undertaking electrical thermography must possess both thermographic competence and electrical competence. These two skill sets are complementary and essential for safe, accurate, and meaningful inspections.
Thermography Competence
Practitioners should be trained and certified in accordance with recognised thermography standards.
Recommended competence levels include:
- PCN/ITC Category 1 – foundational competence for data capture and basic interpretation
- PCN/ITC Category 2 – required for detailed analysis, diagnosis, and report sign‑off
- PCN/ITC Category 3 – for advanced diagnostics, programme design, and technical leadership
These levels ensure practitioners understand thermal physics, emissivity, measurement uncertainty, and the correct application of imaging techniques.
Electrical Competence
Electrical competence is critical for understanding how electrical systems operate, how they fail, and how to work safely around energised equipment.
While the 18th Edition (BS 7671) provides important grounding in wiring regulations, it does not provide sufficient knowledge of:
- Electrical failure mechanisms
- Load behaviour and imbalance
- High‑resistance joints and connection degradation
- Thermal signatures associated with electrical faults
- Switchgear construction and internal componentry
- Safe working practices around live assemblies
- HV system architecture and fault modes
To competently perform electrical thermography, practitioners should have:
1. Practical electrical experience
Hands‑on experience with electrical installations, maintenance, or inspection is essential. This includes familiarity with:
- Distribution boards and switchgear
- MCCs and control panels
- Busbar systems
- Transformers and HV apparatus
- Cable terminations and jointing practices
2. Understanding of electrical failure modes
Practitioners must be able to recognise and interpret thermal patterns associated with:
- Loose or deteriorated connections
- Overloaded circuits
- Phase imbalance
- Harmonic loading
- Mechanical wear in contactors and breakers
- Cooling issues in HV equipment
- High‑resistance joints and bolted connections
3. Knowledge of electrical safety principles
This includes:
- Live working boundaries
- Arc‑flash risk and mitigation
- Safe isolation principles (even when not isolating)
- PPE selection and limitations
- Safe access to switchrooms and substations
4. HV‑specific competence (where applicable)
- For practitioners inspecting HV systems, additional knowledge is required, such as:
- HV switchgear types and construction
- Insulator and bushing behaviour
- Transformer cooling systems
- Common HV failure mechanisms
- Safe approach distances and substation protocols
Combined Competence
Electrical thermography is most effective when practitioners possess both:
- The technical ability to capture and interpret thermal data
- The electrical understanding to diagnose the underlying cause safely and accurately
This combined competence ensures that findings are meaningful, actionable, and aligned with industry best practice.
Equipment Specification
The quality and suitability of thermal imaging equipment has a direct impact on the accuracy, reliability, and credibility of an electrical thermography survey. Practitioners must ensure that the equipment they use meets the technical requirements of electrical inspection and is capable of capturing meaningful, repeatable, and diagnostically useful data.
All equipment used for electrical thermography should comply with the principles and performance expectations set out in ISO 18434‑1, which defines requirements for condition monitoring using thermography, including measurement practices, equipment capability, and data quality.
Minimum Equipment Standards
Thermal imaging cameras used for electrical thermography must not be low‑specification devices or phone‑based clip‑on attachments. These devices typically lack the resolution, optical quality, temperature measurement accuracy, and focus control required for professional electrical diagnostics.
Key Technical Requirements
1. Optical Focus Capability
- Cameras must have optically focusable lenses (manual or motorised).
- Fixed‑focus or “focus‑free” devices are not suitable, as they cannot reliably resolve small electrical components or terminations.
- Accurate focus is essential for correct temperature measurement and anomaly detection.
2. Spatial Resolution and IFOV
- The camera’s Instantaneous Field of View (IFOV) must be appropriate for the target size and distance.
- Practitioners must ensure that the smallest component of interest (e.g., a cable lug, breaker terminal, busbar joint) occupies enough pixels to produce a reliable measurement.
- Cameras with insufficient resolution or poor IFOV performance risk missing defects or producing misleading results.
3. Thermal Sensitivity
- Equipment should have adequate thermal sensitivity (NETD) to detect small temperature differences typical of early‑stage electrical faults.
- Higher sensitivity enables clearer identification of subtle anomalies such as high‑resistance joints or phase imbalance.
4. Temperature Range
- The camera must support a temperature range suitable for electrical applications, including elevated temperatures associated with overloaded or deteriorating components.
- HV applications may require extended temperature ranges to capture hotter components safely and accurately.
5. Calibration and Maintenance
- Cameras must be regularly calibrated in accordance with manufacturer recommendations and in line with ISO 18434‑1 expectations for measurement accuracy.
- Practitioners should maintain calibration records as part of their quality assurance process.
6. Appropriate Lensing
- Wide‑angle, standard, and telephoto lenses may be required depending on the environment.
Inspection Approach
A structured, repeatable, and fully auditable methodology is essential for delivering consistent and reliable electrical thermography surveys.
Recommended Approach
- Conduct surveys under normal load conditions, ensuring that equipment is energised and operating in a representative state.
- Follow a systematic inspection route that covers all relevant energised assets, ensuring no equipment is overlooked.
- Capture thermal and visual images for every asset inspected, not only those with identified anomalies. This creates a complete audit trail and supports future comparison, trend analysis, and verification of survey completeness.
- Record all relevant contextual information, including load conditions, environmental factors, emissivity settings, reflected temperature values, and any access limitations.
- Inspect electrical assets with covers removed where appropriate, provided this has been suitably risk‑assessed, authorised by the duty holder, and carried out in accordance with site safety rules and statutory requirements. Removing covers can significantly improve diagnostic accuracy by exposing terminations, busbars, and internal components that may otherwise be obscured.
- Apply standardised processes and documentation, ensuring consistency between practitioners and across multiple survey cycles.
- Ensure all findings are traceable, with image references, asset IDs, and location details clearly linked within the final report.
This approach ensures that the survey is not only technically robust but also transparent, repeatable, and defensible—key expectations for professional electrical thermography.
Safety
Electrical thermography involves working in close proximity to energised equipment, and safety must be the primary consideration throughout the inspection process. Practitioners must ensure that all activities are carried out in accordance with statutory requirements, site rules, and recognised industry best practice.
Key Safety Requirements
- Comprehensive risk assessment: All inspections must be supported by a suitable and sufficient risk assessment that considers electrical hazards, arc‑flash potential, access constraints, environmental conditions, and the specific characteristics of the equipment being inspected.
- Safe working near live equipment: Practitioners must understand and respect safe approach distances, arc‑flash boundaries, and the limitations of their PPE. Only trained and competent personnel should work in areas where live conductors are exposed.
- Removal of panel covers:
- Electrical assets may be inspected with covers removed only where it is safe, justified, and formally risk‑assessed.
- Removal must be authorised by the duty holder or responsible person on site.
- Practitioners must ensure that removing covers does not expose them or others to unacceptable risk, and that appropriate control measures (e.g., barriers, insulated tools, PPE) are in place.
- Where covers cannot be safely removed, this limitation should be recorded and reflected in the report.
- Use of appropriate PPE: Practitioners must wear PPE suitable for the environment and the equipment being inspected, including arc‑rated clothing where required.
- Clear communication and coordination: Practitioners must liaise with site representatives to ensure safe access, confirm operational status of equipment, and coordinate any switching or isolation required for safe inspection.
- Environmental and situational awareness: Conditions such as confined spaces, elevated working areas, poor lighting, or high ambient temperatures must be considered and managed.
- Documentation and traceability: All safety considerations, access limitations, and deviations from standard practice must be documented to ensure transparency and accountability.
This safety framework ensures that electrical thermography is carried out responsibly, with full regard for the risks associated with working on or near energised electrical systems.
Reporting Criteria
Reporting is a critical component of electrical thermography and must provide a clear, accurate, and fully auditable record of the inspection. Reports should follow recognised standards and present findings in a way that supports safe, informed decision‑making by duty holders, maintenance teams, and insurers.
Standards and Structure
Reports should be aligned with the principles and reporting expectations set out in ISO 18434‑1, including:
- Clear documentation of inspection conditions
- Accurate temperature measurements
- Traceable image records
- Consistent severity classification
- Transparent methodology
Auditability Requirements
To ensure the survey is fully auditable:
- Thermal and visual images must be provided for every asset inspected, not only those with identified anomalies.
- This demonstrates survey completeness
- Supports future comparison and trend analysis
- Provides evidence for insurers and compliance bodies
- Each image must be clearly referenced with:
- Asset ID or description
- Location
- Panel or circuit designation
- Date and time stamp
- Load conditions, environmental factors, emissivity settings, and reflected temperature values must be recorded to support measurement accuracy and repeatability.
- Any access limitations or safety restrictions (e.g., covers that could not be removed) must be documented transparently.
- All findings must be traceable back to the original thermal and visual images.
Content of a Professional Report
A high‑quality electrical thermography report should include:
- Executive summary with key findings and recommended actions
- Methodology statement referencing ISO 18434‑1 and site‑specific considerations
- Asset‑by‑asset results, including:
- Thermal and visual images
- Temperature measurements (absolute and differential)
- Load conditions
- Severity rating (e.g., low, medium, high, critical)
- Suspected root cause
- Recommended remedial actions
- Prioritisation of defects, enabling maintenance teams to plan interventions effectively
- Safety notes, including any hazards observed during inspection
- Appendices containing asset lists, calibration details, and any deviations from standard practice
Severity Assessment
Severity ratings should be based on:
- Temperature rise above comparable phases or components
- Load conditions at the time of inspection
- The criticality of the asset
- The likelihood and consequence of failure
- Relevant industry norms and engineering judgement