Thermography Inspection for Preventive Maintenance
Thermography inspections are a cornerstone of electrical preventive maintenance, used to identify potential issues in equipment like solar modules, breakers, switchgear, and transformers. By detecting infrared energy, these inspections reveal thermal abnormalities that can signal faults before they lead to complete equipment failures.
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Thermographic surveys should be performed during periods of maximum possible loading.
Source: NFPA 70B, Sub-Section, Test Parameters.
However, a common misconception persists, many believe thermography inspections can be effectively performed when electrical equipment is offline or de-energized. This is incorrect, as performing such inspections of offline equipment will produce inaccurate readings, rendering results useless. Industry standards, such as NFPA 70B and ANSI/NETA, mandate that electrical equipment must be under load to generate meaningful thermal data. Conducting inspections under operational conditions ensures accurate detection of issues, safeguarding personnel and equipment while enhancing system reliability and preventing costly downtime.
Capturing a thermal image of a short circuited solar panel
Importance of Load in Thermography Inspections
Thermography inspections rely on load to generate detectable heat in electrical systems, making operational conditions essential for accurate results. When electrical equipment like breakers, switchgear, or transformers is under load, current flows through conductors, producing heat due to resistance, which infrared cameras detect as thermal signatures. These signatures reveal anomalies such as loose connections or overloaded circuits, which are invisible when equipment is offline. Without a load on the system, no current flows, and thus no heat is generated. If no heat is generated it renders thermal readings meaningless, causing a high potential for missing critical faults.
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For example, a compromised crimp connection may appear normal when offline but show a significant temperature rise under load. Inspecting equipment in an operational state ensures that thermography can identify defects, enhancing safety by preventing unexpected failures and protecting personnel. Adhering to load requirements, as mandated by industry standards, is a crucial step for preventive maintenance and avoiding costly downtime.
Thermal image of energized high voltage transmission line
How Load Impacts Delta T
Delta T (ΔT) refers to the temperature difference between similar electrical components under load or between a component and ambient air. This is a critical metric in thermography inspections. Loads generate heat through current flow, enabling infrared cameras to detect anomalies like loose connections or overloads. Higher loads amplify stress on faulty components, resulting in more extreme ΔT differences.
For instance, a loose termination under a heavy load experiences increased resistance, producing a pronounced hot spot—potentially 20–50°F hotter than a properly functioning component—while the same connection under no load shows no thermal anomaly. This heightened ΔT is crucial for identifying defects that could lead to failures. For example, a damaged breaker may exhibit a significant ΔT under high load but will be seen as undetectable when offline. To ensure accurate ΔT measurements, ammeter readings verify comparable load conditions, aligning with standards like NFPA 70B, which emphasize live loads for reliable thermography results.
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Review of Industry-Accepted Standards
Industry standards universally mandate that electrical equipment be under load during thermography inspections to ensure accurate detection of thermal anomalies. These standards provide clear guidelines to enhance safety and reliability in electrical systems.
NFPA 70B (2023) – Standard for Electrical Equipment Maintenance
Section 7.4 of NFPA 70B (2023) requires thermography to measure Delta T (temperature differences) between similar components under similar loading conditions and against ambient air. It emphasizes removing covers for a clear line-of-sight and documenting all findings to ensure precise identification of potential issues.
Infrared thermography shall be used when required to verify temperature differences (L/T) of the following: (1) similar electrical components under similar loading and (2) comparison between electrical components and ambient air temperatures.
Source: 70B-14 Page 3.31
ANSI/NETA MTS (2023) – Standard for Maintenance Testing
The ANSI/NETA MTS (2023) standard mandates infrared inspections under normal operating conditions. This ensures that faults, such as loose connections or overloads, are detected when equipment is active, providing reliable data for maintenance planning. Testing parameters specify the following:
- Inspect distribution systems with imaging equipment capable of detecting a minimum temperature difference of 1° C at 30° C.
- Equipment shall detect emitted radiation and convert detected radiation to visual signal.
- Thermographic surveys should be performed during periods of maximum possible loading.
(Source: NETA MTS (2023), Section 9.3, Page 220.)
ANSI/NETA ATS (2025) – Standard for Acceptance Testing
The ANSI/NETA ATS (2025) specifies that new or retrofitted equipment must be inspected under load within 24 hours of installation. This requirement ensures that newly installed systems are verified for proper operation early in their lifecycle.
Infraspection Institute Standard
The Infraspection Institute Standard for Infrared Inspection of Electrical Systems & Rotating Equipment also requires that equipment be powered on and under sufficient load, preferably its normal operating load, for infrared inspections.
Equipment to be inspected shall be energized and under adequate load; ideally this is normal operating load. For acceptance testing, higher loads may be warranted. (8.2) Subject equipment shall be externally examined before opening or removing any protective covers to determine the possible presence of unsafe conditions. If abnormal heating and/or unsafe conditions are found, the end user or qualified assistant shall take appropriate remedial action prior to commencing the infrared inspection.
Source: Section 8.1 and 8.2 (Page 5.30)
Thermal image of energized substation equipment
Best Practices for Thermography Inspections
To ensure accurate and effective thermography inspections, your thermographer should comply with industry standards and reporting practices. These would include the following:
- Annual Inspections Under Load: Conduct inspections at least yearly with equipment under normal load conditions to capture reliable thermal data.
- Clear Line-of-Sight: Safely remove any covers to provide infrared cameras with an unobstructed view, enabling detection of anomalies like hot spots.
- Certified Thermographers: Employ professionals with a certificate and adequate training to accurately capture and interpret thermal images. This includes being FAA licensed to fly a drone while performing the inspections.
- Ammeter Verification: Use ammeter readings to confirm load conditions, ensuring valid Delta T measurements.
- Detailed Reporting: Record all findings, including ΔT values, per NFPA 70B and Infraspection Institute guidelines.
- Plan Ahead: Schedule inspections 4–6 weeks before maintenance to allow time for ordering repair parts.
- Follow Up Inspection: Verify repairs by reinspecting equipment, ensuring nothing was missed.
These practices optimize thermography’s role in preventing failures and ensuring personnel safety.
Getting Started with Drone Inspections
Accurate thermography inspections require electrical equipment to be under load, as mandated by standards like NFPA 70B, ANSI/NETA, and Infraspection Institute, to detect thermal anomalies that signal potential failures. Conducting inspections under operational conditions ensures reliable Delta T measurements, safeguarding personnel and preventing costly downtime.
Drone-based thermography offers an efficient solution for inspecting equipment like solar modules and switchgear, enabling rapid detection of issues across large systems. At The Drone Life, our FAA-licensed, thermography-certified pilots deliver high-resolution data to optimize maintenance. Don’t risk undetected faults—schedule a free consultation today to learn how our drone thermography services can enhance your electrical system reliability.
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