What Does a Thermographic Survey Actually Detect?

The Principle: Heat Before Failure

Every electrical and mechanical fault produces heat before it fails. A loose cable termination develops resistance. Resistance generates heat. Left undetected, that heat escalates — insulation degrades, arcing begins, and the fault becomes a fire or a catastrophic failure. Thermographic surveys detect this heat signature at the earliest stage, when correction is simple and inexpensive.

The fundamental principle has not changed since thermography was first applied to electrical systems in the 1960s. What has changed is the precision of the cameras, the rigour of the methodology, and the insurance industry's recognition of thermography as a mandatory maintenance discipline.

Electrical Faults Detected by Thermography

Electrical thermography is the most common application of infrared inspection in commercial and industrial settings. A qualified thermographer scanning energised electrical equipment under live-load conditions will detect the following:

• Loose or high-resistance terminations — the most common finding. A cable that is under-torqued or corroded develops contact resistance, producing localised heat at the termination point. ΔT readings above ambient of 15°C or more indicate serious risk.
• Overloaded circuits and phase imbalance — circuits drawing current beyond their rated capacity show elevated temperatures across the conductor and breaker. Phase imbalance in three-phase systems is visible as asymmetric heating across phases.
• Failing breakers, contactors, and isolators — internal wear or carbon tracking causes resistance build-up inside switching devices, visible as hot spots that are not present in adjacent identical devices.
• Busbar heating and corroded bus joints — main switchgear busbars develop elevated temperatures at joints, bolted connections, and tap-off points where contact resistance increases over time.
• Neutral and earth conductor overloads — neutral conductors in unbalanced three-phase installations or installations with significant harmonic loads carry elevated current, detectable as differential heating versus phase conductors.
• PFC capacitor failures — power factor correction capacitor banks develop internal faults and overheating, detectable before they fail explosively.
• Incorrect cable sizing — undersized conductors run hotter than correctly sized equivalents at the same current, identifiable through comparative temperature measurement.

Mechanical Faults Detected by Thermography

Mechanical thermography monitors rotating and static equipment for friction, lubrication, and alignment faults. Applications include motors, gearboxes, conveyor systems, pumps, fans, and compressors.

• Bearing failures — failing or under-lubricated bearings generate heat through increased friction. Early-stage bearing degradation is detectable weeks before audible noise or vibration become apparent.
• Misalignment — shaft misalignment between coupled equipment produces asymmetric heating at the coupling point and across bearing housings.
• Belt tension issues — overtensioned or slipping belts generate friction heat detectable at pulleys and belt surfaces.
• Blocked or restricted cooling — motors with blocked ventilation paths or clogged cooling fins show elevated winding and frame temperatures.
• Overloaded motors — motors running above rated load show elevated temperatures across the frame and terminal box.

Building and Moisture Defects

Infrared cameras are equally effective for building envelope inspections, moisture detection, and insulation assessment:

• Moisture ingress in roofs and walls — wet insulation has different thermal mass to dry material, producing distinctive cool patches during thermal drift periods (shortly after sunset or sunrise).
• Insulation voids and deficiencies — missing or inadequate insulation in building envelopes shows as thermal bridging — heat loss in winter, heat gain in summer.
• Concealed water damage — water infiltration behind cladding, under screed, or within cavity walls is detectable before visible damage appears.

What Thermography Cannot Detect

Being precise about limitations is as important as stating capabilities. Thermography detects surface temperature variations. It cannot:

• Detect faults that are not generating heat at the time of inspection
• See through surfaces with very low thermal conductivity
• Confirm the cause of a hot spot — only that a temperature anomaly exists
• Substitute for electrical testing (insulation resistance, earth continuity) or mechanical condition monitoring

This is why load conditions at the time of survey matter. SANS 10142-1 and insurance underwriter requirements specify surveys be conducted at or above 40% of rated load. Below this threshold, fault signatures may be too small to detect reliably.

The Insurance Significance

A professional thermographic survey report documents the thermal condition of your electrical and mechanical infrastructure at a point in time. For insurers, it provides evidence that proactive maintenance is in place, that known faults have been identified and prioritised for correction, and that the risk of an electrical fire has been assessed and mitigated. This documentation is increasingly required at policy renewal and is a material factor in premium assessment for commercial and industrial properties.