Thermographic Inspection of Electrical Panels: Measurement and Reporting
Thermographic inspection: Thermography is the fastest way to see a loose connection before it becomes a failure, provided it is done correctly.
ContentsThermographic inspection images the temperature of connections and components inside an assembly without contact, revealing problems that have not yet become failures. A loose busbar bolt or an oxidised terminal starts heating long before any breaker trips, and a thermal camera catches that early warning.
Why it is the first step in predictive maintenance
A large share of electrical failures begins with rising contact resistance. As resistance grows, more power is dissipated at that point, temperature rises, oxidation accelerates and the process feeds itself. The cycle takes weeks or even months. A survey carried out once or twice a year gives the opportunity to break it at the start.
Conditions for a valid measurement
Thermography is only meaningful under load. The general expectation is that at least 40% of rated current is flowing during the survey; below that, temperature differences disappear. Recording the load at the time of measurement is essential for comparison with later surveys. Where covers are to stay closed, infrared windows are used, which is preferable both for safety and for repeatability.
Temperature difference (ΔT) classification
What matters is not absolute temperature but the difference between similar points carrying similar load. Widely used priority bands are as follows:
Common findings
A hot spot alone is not a diagnosis; the pattern has to be interpreted.
| Pattern | Likely cause | Action |
|---|---|---|
| Spot heating at one connection | Loose or oxidised contact | Clean and re-torque with the panel isolated |
| One entire phase hot | Unbalanced load distribution | Redistribute loads between phases |
| Whole cable hot | Overload or undersized conductor | Review the load calculation and cable size |
| Device body hot, terminals normal | Ageing internal component | Plan replacement of the device |
Where measurement errors come from
Wrong readings usually come from surface properties. Bright copper and galvanised surfaces have low emissivity and appear colder than they really are, so applying a matt target label at measuring points is common practice. Measurement cannot be taken through glass or polycarbonate covers, because these materials do not transmit infrared. Reflections are ruled out by repeating the shot from a different angle.
What a report must contain
For a thermography report to be useful next year, it should include:
- Date, ambient temperature and the load at the time of measurement
- A thermal image plus a visual photograph from the same angle
- Reference point and the ΔT value
- The emissivity setting used and the measuring distance
- Priority band and recommended action
- Comparison with the previous survey
For the design-side counterpart of enclosure temperature, see thermal load and cooling.
Key takeaways: thermographic inspection
- Why it is the first step in predictive maintenance — A large share of electrical failures begins with rising contact resistance.
- Conditions for a valid measurement — Thermography is only meaningful under load.
- Temperature difference (ΔT) classification — What matters is not absolute temperature but the difference between similar points carrying similar load.
- Common findings — A hot spot alone is not a diagnosis; the pattern has to be interpreted.
- Standard source — IEC publication catalogue: iec.ch.
Frequently asked questions
How often should thermography be carried out?
Once a year is common practice for continuously operating industrial sites. On critical processes and where loading varies widely it is increased to every six months. Taking a baseline survey in the first year after commissioning makes later comparisons meaningful.
Does thermography replace maintenance?
No. It is a diagnostic method; findings are then corrected with the equipment isolated, through torque checks, cleaning and component replacement where needed.
Can infrared windows be fitted to any panel?
They can be retrofitted to most metal enclosures, but the opening must be made without compromising enclosure integrity or the degree of protection. See IP protection ratings.
Related articles
- Electrical Panel Maintenance: Periodic Inspection and Safety Recommendations
- Enclosure Material and Powder Coating: How to Choose Correctly
- Cable Zone and Cable Entry Design: Common Switchboard Mistakes
- All technical articles
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