Jun 2017

Thermal Imaging of Electrical Equipment

The benefits of an Electrical Preventive Maintenance (EPM) program at an industrial or commercial facility are well known. In our January 2005 article “Electrical Testing,” we explained that deterioration of electrical equipment is normal, but equipment failure is not a certainty if an effective EPM program identifies and recognizes factors that can accelerate deterioration and provides measures for coping with them and addressing deficiencies. The majority of property losses involving electrical equipment are related to poor operating conditions (i.e., overload, deteriorated insulation, loose connections) or environment (i.e., poor ventilation, dirty or corrosive environments, contamination, combustible storage). Typically, an effective EPM program includes performing regular visual inspections, maintaining good housekeeping practices, and performing electrical inspections and tests including thermal imaging (infrared (IR) scans) and insulation-resistance measurements.

This article provides further information on the benefits and recommended frequencies of thermal imaging. It also addresses how to inspect higher voltage electrical panels that may not be safe to open while energized.

Thermal imaging can detect deteriorated insulation or poor physical connections in switchgear/equipment before they become major problems. Scans should be conducted at least once for a facility that has electrical equipment considered essential to production or is a significant fire exposure. At some smaller locations, a survey may not be economically warranted unless the fire exposure is unusually high. Newly installed equipment should also be included in the thermal imaging program.

The frequency of follow-up IR scans typically depends on the number of problems found during the initial survey. At large facilities with a harsh environment, IR scans may be required every six months for the first few years.

The following table lists some electrical equipment that should be IR tested as well as the recommended frequency of testing.


Test Frequency

Electrical Bus Bars

3 to 5 years


1 to 5 years depending upon electrical rating and type of switch

Rotating Machinery

1 to 3 years


Dry: 1 to 3 years;  Liquid: 3 to 5 years

The testing intervals may be gradually reduced as the number of discovered issues decreases (trending analysis) and causes are properly addressed.

For a more detailed breakdown of testing frequencies and equipment that should be part of an EPM program, see NFPA Standard 70B, Recommended Practice for Electrical Equipment Maintenance or FM Global Property Loss Prevention Data Sheet 5-20, Electrical Testing.

Due to recent emphasis on personnel safety, many electrical panels, including some that were previously inspected/tested, can no longer be opened while energized due to the equipment’s calculated voltage, incident energy rating or company regulations. In order to provide complete coverage of all electrical assets by your thermal imaging predictive maintenance program, IR windows (or IR view ports) can be installed.

These view ports comply with regulatory standards (including OSHA, NFPA 70E, etc.) and similar electrical safety mandates. The view ports eliminate inherently high risk tasks, such as removing panels or opening hinged doors, making IR scans safer for personnel, equipment and processes. Workers are able to perform IR scans while keeping energized equipment closed and in normal operating condition.

To some degree, all view ports have a limited field of view within the switchgear enclosure. Square IR windows provide best in class field of view, up to 65% more optic area than similar sized round windows. To maximize the effectiveness of an IR scanning program using view ports, the ports should be installed strategically in areas where problems are likely to occur or have occurred in the past. These locations typically include the rear panels of switchgear enclosures where main bus bar bolted connections, main circuit breaker switchgear contacts, and/or cable terminations can be viewed.

IR windows should be installed by a licensed electrician to help ensure proper window placement and field of view, and to ensure the arc-resistant integrity of the switchgear is not compromised.

Reference Documents:
NFPA Standard 70B, Recommended Practice for Electrical Equipment Maintenance
FM Global Property Loss Prevention Data Sheet 5-20, Electrical Testing