Electrical Thermography Severity Scale Explained: ΔT, Priorities, and NFPA 70B/70E Guidance
Severity Isn’t a Color — It’s a Defensible Decision
In professional electrical thermography, the most valuable skill isn’t finding a hot spot — it’s translating temperature data into a consistent, repeatable severity decision that supports electrical maintenance best practices and electrical safety expectations.
What Is Thermography Severity?
Thermography severity is the classification of thermal findings based on temperature rise (ΔT) relative to a defined reference, used to prioritize maintenance actions and evaluate electrical reliability risk in a consistent, defensible way.
Why Severity Matters in the CTE™ Program
Severity gives your findings a standardized language so teams can prioritize work, schedule repairs, and reduce risk without guessing.
When you align severity with maintenance expectations (NFPA 70B) and electrical safety practices (NFPA 70E), thermography becomes a reliability tool — not just a collection of images.
Severity protects you professionally: it creates a defensible, repeatable method rather than “it looked hot.”
Severity Is the Bridge Between Thermography and Reliability
A thermal camera doesn’t “diagnose” a problem — it reveals thermal behavior. Severity is the discipline of turning that behavior into a clear maintenance decision. When severity is consistent, your program becomes predictable: inspections drive prioritization, prioritization drives action, and action drives reliability.
In the Certified Thermal Electrician™ approach, severity is built around ΔT (temperature rise) because ΔT provides a stable comparison across different ambient conditions and environments. A 120°F lug in a 110°F enclosure is not the same condition as a 120°F lug in a 70°F area — ΔT clarifies the risk story.
Where NFPA 70B and NFPA 70E Fit in a Thermography Program
Thermography sits at the intersection of maintenance and electrical safety. NFPA 70B establishes expectations for proactive maintenance and condition-based decisions. NFPA 70E establishes expectations for electrical safety work practices — including planning, risk assessment, and controls when approaching exposed energized conductors and circuit parts.
Severity supports maintenance prioritization. It helps you decide what should be addressed now, what should be scheduled, and what should be trended — without overreacting to normal operating heat.
The goal is to gather useful data while controlling risk. Severity affects the next steps: if a condition appears critical, you plan verification and corrective action with appropriate safety controls.
Important reminder
Thermography can be performed safely — but only when it’s planned and executed with proper electrical safety practices. Severity is not permission to “push closer.” It’s a tool to plan the next best maintenance action.
The Big 6: What Changes Severity Decisions in the Real World
Thermal patterns are load-driven. Document load when possible. Avoid overconfidence when equipment is lightly loaded unless you clearly state limitations.
A great image with a poor reference can create false urgency. Like-for-like comparisons under the same load are among the strongest real-world references.
Shiny metals can “lie.” Set emissivity appropriately, manage reflections, and use repeatable targets (tape/painted surfaces where allowed) to improve reliability.
Airflow, wind, covers, and enclosure heat soak can change what the camera sees. Note ventilation and whether doors/covers are open or closed.
If the target is smaller than your spot size, readings blend with background. Maintain reasonable angles and confirm you are measuring the actual component surface.
A small ΔT that is rising inspection-to-inspection can be more important than a one-time moderate ΔT that remains stable.
Making Severity Actionable: What Your Report Must Include
A severity label without context is just a color. A CTE-quality report supports a maintenance decision that others can trust. Your finding should clearly communicate what you saw, how you referenced it, and what the next action should be.
CTE™ reporting checklist (no fluff)
Include asset identification and location, load context when available, the reference method used (ambient, like-for-like, or trend), the measured temperature and reference temperature used to calculate ΔT, thermal and visual images with the target clearly identified, notes on limitations (emissivity estimate, reflections, cover position, distance/angle), and a clear recommendation tied to the severity logic.
Severity and the “False Alarm” Problem
One of the fastest ways to lose trust in a thermography program is to flag everything as urgent. Over-calling severity creates alarm fatigue and wastes maintenance resources. Under-calling severity can allow deterioration to continue until a failure occurs. The CTE™ framework exists to keep severity consistent and credible.
“Normal” is still valuable data. Green findings help establish baselines, confirm phase-to-phase balance, and validate improvements after repairs.
Yellow is the professional curiosity zone. Confirm the reference, validate emissivity assumptions, consider trending, and document conditions clearly.
Orange is where you expect a real contributor such as termination quality, imbalance, overload, damaged components, harmonic-related heating, corrosion, or mechanical looseness.
Red indicates serious risk. The right response is a coordinated plan: confirm conditions, coordinate with operations/maintenance, and proceed with appropriate safety controls.
The CTE™ Standard: Repeatable, Defensible, Teachable
The Certified Thermal Electrician™ Program trains severity as a system: select references correctly, document limitations, interpret ΔT consistently, and produce recommendations that maintenance teams can execute. When severity is standardized, multiple technicians can inspect the same facility and still speak the same language — even across seasons and operating conditions.
Professional note: This article is educational and supports thermography decision-making. It is not a substitute for your organization’s electrical safety program, procedures, or engineered risk assessments. Always follow applicable NFPA 70E work practices, site-specific rules, and manufacturer instructions.
