Infrared thermography for electrical systems

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.

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:

1. Assign each finding to a responsible person and a repair date based on severity.
2. Repair under lockout, finding and fixing the root cause, not just retightening. A connection that overheated may have damaged the conductor or the terminal.
3. Rescan the repaired equipment under load to confirm the fix.
4. 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.

Planning a survey: what to have ready

A survey goes faster and finds more when the site is prepared. Before the thermographer arrives:

• A list or single-line diagram of the equipment to be scanned, in a sensible walking order
• Equipment labels that match the drawings, so findings can be located later
• Arc flash labels and the site's energized work procedures available for the qualified electrical worker who will open covers
• Access arranged to electrical rooms, locked panels and rooftop or outdoor equipment
• The survey scheduled for a time of normal or high load, not a holiday shutdown
• Last year's report on hand, so recurring findings can be compared

A typical case

During an annual scan of a commercial building, the thermographer finds that one phase of a feeder breaker in the main switchboard is noticeably warmer than the other two, while a clamp meter shows the three phases carrying similar current. Because the load is balanced, the temperature difference points to the connection rather than the circuit. The report ranks it as a priority finding, with a thermal image, a visible photo and the load at the time.

The building schedules a short outage. Under lockout, the electrical contractor finds the lug discoloured and the conductor strands darkened at the termination. Simply retightening would have left damaged material in place, so the contractor cuts back the conductor to clean copper, replaces the lug and torques it to the manufacturer's value. A rescan under load a few weeks later shows all three phases at similar temperatures, and the finding is closed.

Common mistakes

• Scanning at light load. A survey done at night or during a shutdown can miss problems that only show under full current.
• Trusting the number on the screen. Reflections and low-emissivity surfaces can make a hot part look cool and a cool part look hot.
• Opening live panels without the right controls. The survey must follow your energized work procedures every time.
• Not closing findings. A report that sits on a shelf finds the same hot spot next year, if it has not failed by then.

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