Reflectivity in Electrical Thermography: How It Affects Thermal Imaging and How to Control It

Technical guidance for Certified Thermal Electrician™ professionals

Thermal cameras do not actually “see” temperature — they detect infrared radiation. In electrical thermography, one of the biggest sources of error is reflectivity: shiny or low-emissivity surfaces that reflect IR from other objects instead of accurately showing their own temperature.

For a Certified Thermal Electrician™, understanding reflectivity is essential to avoid false readings, misdiagnosed “hot spots,” and incorrect NFPA 70B severity classifications.

🔥 1. The Physics Behind Reflectivity

All materials interacting with infrared energy can:

• Emit IR (emissivity)
• Absorb IR
• Reflect IR (reflectivity)

For opaque electrical components (metals, most plastics), transmissivity in the IR band is essentially zero. That means the two dominant properties are:

• Emissivity (ε) – how well the surface emits IR energy.
• Reflectivity (ρ) – how much IR energy it reflects from the environment.

For most metals used in electrical equipment:
ε + ρ ≈ 1

So when emissivity is low (shiny aluminum, polished copper), reflectivity is high. These surfaces behave like IR mirrors and can reflect:

• Hot transformers
• Other energized components
• Sunlight
• Space heaters or process equipment
• You and your own body heat

⚡ 2. Why Reflectivity Is Dangerous in Electrical Thermography

Reflective surfaces can create serious interpretation errors:

• False hot spots – the camera sees a reflection of a hot object, not a hot component.
• False cold spots – an overheated component reflects a cooler ceiling or wall.
• Wrong ΔT values – inaccurate temperature rise calculations for NFPA 70B severity.
• Incorrect maintenance actions – tightening good connections, missing failing ones.

NFPA 70B acknowledges these issues by emphasizing proper camera settings, emissivity, and reflected temperature in infrared thermography sections. Reflectivity must be controlled and accounted for to ensure reliable inspections.

🔩 3. Common Reflective Surfaces in Electrical Systems

Highly reflective or low-emissivity surfaces are found almost everywhere in electrical equipment:

• Bare aluminum lugs and bus bars
• Tin-plated or polished copper lugs
• Stainless steel hardware (screws, bolts, washers)
• Metallic nameplates and cover plates
• Breaker handles and toggle surfaces (some plastics are semi-reflective in IR)
• Conduit bodies and fittings with bright finishes
• Painted metal with glossy finishes

These surfaces can easily reflect hot conductors, transformers, other breakers, or even the thermographer’s own body heat into the camera.

🧠 4. How the Thermal Camera “Sees” a Reflective Surface

A thermal camera measures total infrared radiation reaching the detector from a particular direction. For a reflective surface:

Total observed IR = Emitted IR + Reflected IR

On a high-reflectivity metal:

• Emitted IR is low (low emissivity)
• Reflected IR is high (large portion of incident energy is reflected)

This means:

• The camera may show the temperature of the reflected environment instead of the component.
• Adjusting the emissivity setting alone cannot fix reflection errors.

Reflectivity must be managed physically (angle, surface treatment, or alternate target), not just mathematically.

🛠️ 5. Practical Techniques to Handle Reflectivity in Electrical Thermography

A Certified Thermal Electrician™ must be able to recognize reflective surfaces and apply the right mitigation method.

📐 Technique 1: Change Your Viewing Angle

Reflective surfaces behave like mirrors at certain angles. If you view a shiny lug straight on, you may be capturing a reflection of something else.

• Avoid imaging perfectly perpendicular to shiny metal.
• Shift your position horizontally or vertically.
• Use an angle of approximately 30°–60° relative to the surface.

By changing position, you can often make the “hot” reflection disappear or drastically change, revealing the true surface condition.

🚶 Technique 2: Move Yourself and Identify Reflected Sources

If an apparent hot spot moves or changes intensity simply because you moved your body or the camera:

• It is very likely a reflection, not a true emission.

Look around for:

• Hot nearby transformers or bus ducts
• Sunlit windows or skylights
• Space heaters or process equipment
• Your own reflection on bright bus or enclosures

🎯 Technique 3: Apply a High-Emissivity Target (When Safe)

When the system can be safely de-energized, you can apply a small high-emissivity “target” to the surface:

• Matte black electrical tape
• High-emissivity stickers
• Nonconductive, flat black marking in a small area

These surfaces have emissivity typically in the 0.95–0.97 range and give far more accurate temperature readings compared to exposed shiny metal.

Important: Application of any physical material to exposed energized parts must follow NFPA 70E. Do not apply tape or markings to energized lugs.

🧵 Technique 4: Use the Insulation or Adjacent High-Emissivity Surface

When direct surface treatment is not possible, you can:

• Measure the insulation jacket near the termination.
• Measure the breaker body instead of shiny screw heads.
• Measure nearby bus insulation or epoxy-coated sections.

These materials have higher emissivity and can be used as a thermal proxy for conductor heating, especially for trend analysis and comparative evaluation.

📊 Technique 5: Compare Similar Components (NFPA 70B Approach)

NFPA 70B emphasizes comparing:

• Phase A vs. Phase B vs. Phase C
• Feeder vs. feeder
• Breaker vs. identical breaker under similar load

When multiple components have similar surface properties and reflectivity, relative temperature differences are still meaningful even if the absolute temperature is slightly distorted by reflection.

📏 6. Reflectivity and NFPA 70B ΔT Severity Classification

NFPA 70B allows severity classification based on:

• ΔT above ambient, and/or
• ΔT above similar components.

Reflectivity has the most impact on absolute temperature values. However, when all three phases or similar components have the same reflective properties, differences (ΔT) between them still help to identify anomalies.

Example:

• Phase A lug: 82°F
• Phase B lug: 84°F
• Phase C lug: 120°F

Even if absolute values are skewed by reflectivity, Phase C shows a ΔT of about 20°C or more above the others — a potential high-severity condition under NFPA 70B severity guidelines.

🚫 7. Common Reflectivity Mistakes in Electrical Thermography

• Assuming every hot-looking lug is truly hot – often it’s reflecting a nearby heat source.
• Relying only on emissivity setting – emissivity correction does not remove reflections.
• Imaging shiny breaker handles or screws – they often show reflections of your own body or surroundings.
• Scanning in direct sunlight without accounting for reflections – sunlit reflections can completely mask real heating.
• Ignoring camera position – standing directly in front of reflective bus or gear often results in imaging your own heat.

🏆 8. Summary for Certified Thermal Electricians™

Reflectivity is one of the primary sources of error in electrical thermography. A Certified Thermal Electrician™ must be able to:

• Identify reflective surfaces in electrical equipment.
• Use proper viewing angles and positions to minimize reflections.
• Apply high-emissivity targets when it is safe to do so.
• Use insulation, breaker bodies, or other high-emissivity surfaces as proxy measurement points.
• Apply NFPA 70B’s comparison-based methods to determine real ΔT and severity.
• Avoid false hot/cold readings caused by reflections of external heat sources.

When reflectivity is understood and controlled, thermal imaging becomes a precise, repeatable, and powerful tool for electrical diagnostics, code-aligned maintenance, and preventive reliability work.

To learn more about the Certified Thermal Electrician™ Program, visit:
https://ThermalElectrician.com