Infrared thermography uses a thermal camera to see heat in electrical equipment while it is energized and under load. Loose connections, overloaded conductors and failing components run hotter than they should, often long before they fail. A thermographic survey finds these hot spots so they can be repaired during a planned shutdown instead of after a fire or outage.
Why electrical problems show up as heat
Current flowing through resistance produces heat. A healthy connection has very low resistance, so it stays close to the temperature of the conductors around it. When a connection loosens, corrodes or is poorly made, its resistance rises and so does its temperature. Heat speeds up oxidation, which raises resistance further, and the problem gets worse until the connection fails.
Other causes of abnormal heating include:
- Overloaded circuits or conductors that are undersized for the load
- Unbalanced loads across phases
- Failing breakers, fuses, contactors and fuse clips
- Harmonics heating neutrals and transformers
- Internal faults in transformers, motors and bus
What can be scanned
- Switchgear, switchboards and distribution panels
- Motor control centres, starters and drives
- Transformers and their connections
- Busway and bus plugs
- Disconnects, fused switches and transfer switches
- Generator output connections
- Motors and their bearings and couplings
- Large lighting and HVAC panels
What makes a good survey
Load
Thermography only works when current is flowing. Equipment at light load may hide a problem that would show at full load. Schedule surveys when the building or process is running normally, and record the load on each piece of equipment at the time of the scan so the findings can be put in context.
Line of sight
Thermal cameras cannot see through closed metal covers or most glass. For most panels, covers must be opened or removed while the equipment is energized, which exposes people to shock and arc flash hazards. Infrared windows installed in the covers of larger equipment let scans be done with covers closed, which reduces that exposure.
Emissivity and reflection
Different surfaces give off infrared energy differently. Shiny metals such as bare copper, aluminum and polished bus reflect heat from their surroundings and can give misleading readings. A trained thermographer understands this, takes readings from suitable surfaces and adjusts camera settings, rather than trusting a number on the screen.
Qualified people
Two skills are needed: interpreting thermal images correctly, and working safely around energized equipment. Thermographers are typically trained and certified through recognized programs at different levels. Opening live equipment must be done by, or under the direct control of, a qualified electrical worker, following your arc flash program and CSA Z462.
Safety first. Removing covers from energized equipment is energized electrical work. It needs a hazard assessment, the right arc-rated PPE, approach boundaries and qualified workers. Never open live equipment just to take a picture. See arc flash basics.
Reading the results
Findings are usually ranked by severity based on the temperature rise, either compared with similar components under similar load or compared with ambient temperature. Industry testing organizations publish severity tables for this, and a good report states which criteria it uses. A typical report includes, for each finding:
- A thermal image and a matching visible-light photo
- The location and equipment identification
- Measured temperatures and the comparison used
- The load at the time of the scan
- A severity ranking and recommended action
Findings range from "monitor at the next survey" to "repair immediately." Serious findings may call for reducing load or arranging an outage right away.
After the survey
A thermographic survey has value only if the findings are fixed. Good practice:
- Assign each finding to a responsible person and a repair date based on severity.
- Repair under lockout, finding and fixing the root cause, not just retightening. A connection that overheated may have damaged the conductor or the terminal.
- Rescan the repaired equipment under load to confirm the fix.
- Keep reports and images so you can compare from one survey to the next.
Thermography is a complement to, not a replacement for, de-energized maintenance such as cleaning, torque checks and testing. Our guide on switchgear and panel maintenance covers how the two fit together. Thermal cameras are also used on building envelopes; see thermal imaging in building inspections.
How often to scan
Many facilities scan critical electrical equipment once a year. Insurers sometimes require or encourage periodic surveys, and critical sites such as data centres and hospitals may scan more often. New installations and major changes are worth scanning once they are carrying normal load.
How ehZee can help
Our electrical system inspections look at the condition of your distribution equipment and maintenance records, and can help you plan a thermographic survey, interpret the results and coordinate repairs with your electrical contractor.
Common questions
Can thermography be done without opening panels?
Only where infrared windows or viewing ports are installed, or for equipment with exposed connections. Otherwise covers must be removed by qualified workers with the right precautions.
Does a clean scan mean the equipment is fine?
It means no abnormal heating was seen at that load. It does not test insulation, breaker trip function or mechanical condition, which need other tests.