🌡️ Thermal Imaging Reference

Infrared Thermography Inspection Guide, Emissivity Tables & Severity Criteria

Severity Criteria

Emissivity Tables

Calculators

Electrical Limits

Mechanical

Best Practices

🔥 NETA MTS Delta T Severity (vs Similar Component)

Compare temperature rise above a similar component under similar loading conditions.

Priority	ΔT Rise	Severity	Recommended Action
1	1-10°C (1-18°F)	Minor	Monitor - possible deficiency
2	11-20°C (19-36°F)	Intermediate	Repair at next scheduled outage
3	21-40°C (37-72°F)	Serious	Repair as soon as possible
4	>40°C (>72°F)	Critical	Repair immediately - failure imminent

Comparing Similar Components

This is the preferred method when comparing identical equipment under the same load. Examples: comparing phases in a 3-phase system, identical breakers, parallel transformers.

🌡️ NETA MTS Delta T Severity (vs Ambient)

Compare temperature rise above ambient air temperature when no similar component is available.

Priority	ΔT Rise	Severity	Recommended Action
1	1-10°C (1-18°F)	Minor	Monitor condition
2	11-20°C (19-36°F)	Intermediate	Warrants investigation
3	21-40°C (37-72°F)	Serious	Repair as time permits
4	>40°C (>72°F)	Critical	Repair immediately

⚠️ Load Considerations

These criteria assume full load conditions. If equipment is at partial load, the severity may be higher than indicated. Temperature rise is approximately proportional to load squared (I²R losses).

🔢 Severity Assessment Calculator

Reference Type

Temperature Unit

Hot Spot Temperature

°C

Reference Temperature

°C

Current Load (%)

Ambient Temperature

°C

Temperature Rise (ΔT)

°C

Severity Level

Serious

SERIOUS

Recommended Action

Repair as soon as possible. Monitor closely until repairs can be made.

📊 Thermal Severity Visual Scale

Failure Rate vs Temperature

The failure rate of electrical components doubles for every 10°C temperature rise above normal operating temperature. A component running 30°C above normal has 8× the failure rate.

📐 Understanding Emissivity

0.0 (Perfect Mirror)0.51.0 (Blackbody)

Emissivity (ε) measures how efficiently a surface emits thermal radiation compared to an ideal blackbody (ε=1.0):

High emissivity (0.9-1.0): Matte, dark, organic surfaces
Medium emissivity (0.5-0.9): Oxidized metals, concrete
Low emissivity (0.1-0.5): Polished/bare metals

⚠️ Why Emissivity Matters

Incorrect emissivity causes significant temperature errors. A polished copper busbar (ε=0.07) measured with ε=0.95 could show 50°C when actually at 150°C!

⚡ Common Industrial Materials - Quick Reference

Material	Emissivity	Notes
Electrical Tape (black)	0.95	Excellent reference
Paint (any color, matte)	0.90-0.95	Most paints work well
Rubber/Plastics	0.90-0.95	Wire insulation
Steel (oxidized)	0.85-0.95	Rusted or heat-treated
Concrete/Brick	0.90-0.95	Building surveys
Steel (polished)	0.10-0.30	Difficult - use tape
Copper (polished)	0.02-0.07	Very difficult!
Aluminum (polished)	0.02-0.10	Very difficult!
Copper (oxidized)	0.50-0.80	Better than polished
Aluminum (oxidized)	0.20-0.40	Still challenging

🔩 Metals Emissivity Table

Metal	Condition	Temp (°C)	Emissivity
Aluminum	Polished	20-100	0.02-0.10
Aluminum	Rough surface	20-50	0.06-0.07
Aluminum	Heavily oxidized	50-500	0.20-0.40
Aluminum	Anodized	20	0.77
Brass	Polished	20	0.03
Brass	Oxidized	20-200	0.40-0.65
Bronze	Polished	20	0.10
Cast Iron	Polished	200	0.21
Cast Iron	Oxidized	100-200	0.64-0.78
Chromium	Polished	150	0.06
Copper	Highly polished	20	0.02
Copper	Polished	20-100	0.03-0.07
Copper	Slightly oxidized	20	0.20-0.30
Copper	Heavily oxidized	20	0.50-0.80
Copper	Black oxidized	20	0.88
Gold	Polished	130	0.02
Inconel	Oxidized	500	0.70-0.85
Iron	Polished	450	0.16
Iron	Fresh rusted	20	0.61
Iron	Heavy rust	20	0.85-0.95
Lead	Polished	130	0.06
Lead	Oxidized	20-200	0.28-0.63
Nickel	Polished	20-100	0.05-0.07
Nickel	Oxidized	200-600	0.37-0.57
Silver	Polished	20-500	0.01-0.03
Stainless Steel	Polished	20	0.07-0.17
Stainless Steel	Lightly oxidized	20-500	0.30-0.50
Stainless Steel	Heavily oxidized	500	0.70-0.90
Steel	Polished sheet	950	0.55
Steel	Oxidized	200	0.79
Steel	Galvanized new	20	0.23
Tin	Polished	20-100	0.04-0.06
Titanium	Polished	200	0.15
Titanium	Oxidized	500	0.50-0.60
Zinc	Polished	230	0.05

🧱 Non-Metals & Other Materials

Material	Type/Condition	Emissivity
Asphalt	Paving	0.93
Brick	Common red	0.93
Carbon	Lamp black	0.95-0.99
Ceramic	Porcelain/glazed	0.90-0.95
Concrete	Rough	0.94
Electrical Tape	Black vinyl	0.95
Enamel	White fused	0.90
Epoxy	Coating	0.89
Glass	Smooth	0.92-0.94
Gypsum	Drywall	0.90-0.92
Ice	Smooth	0.97
Lacquer	Black matte	0.97
Oil (thick film)	Any	0.82
Paint	Black flat	0.97
Paint	White	0.90-0.95
Paint	Aluminum	0.27-0.67
Paper	White	0.90-0.95
Plaster	Rough	0.89
Plastic	ABS	0.91
Plastic	PVC	0.91-0.93
Plastic	Polyethylene	0.85-0.95
Plastic	Nylon	0.87
Rubber	Hard (black)	0.94
Rubber	Soft (gray)	0.86
Skin (human)	Standard	0.98
Soil	Dry	0.92
Water	Distilled	0.96
Wood	Oak planed	0.90
Wood	Pine	0.84

🌡️ Temperature Conversion

Celsius (°C)

Fahrenheit (°F)

Kelvin (K)

Rankine (°R)

Conversion Formulas

°F = (°C × 9/5) + 32

K = °C + 273.15

🪞 True Temperature Calculator

Calculate true object temperature accounting for emissivity and reflected temperature.

Apparent Temperature

°C

Object Emissivity

Reflected Temperature

°C

Atmospheric Trans.

Estimated True Temperature

87.4

°C

Measurement Tips

Reflected temp = average background temperature
Indoor: usually ambient air temperature
Atmospheric transmission ≈ 1.0 for short distances

📊 Load-Adjusted Temperature Rise

Estimate temperature rise at 100% load based on partial load measurement.

Measured ΔT

°C

Current Load

ΔT at 100% Load

26.7

°C (estimated)

Adjusted Severity

Intermediate

IEEE Load Adjustment (I²R)

ΔT₁₀₀% = ΔT_meas × (100/Load%)²

🎯 Distance-to-Spot Ratio Calculator

Calculate minimum target size based on camera D:S ratio and distance.

D:S Ratio

Distance to Target

Minimum Spot Size

mm diameter

Target Should Be

mm (3× spot)

FORD Rule

Focus, Optics, Range, Distance - Target must be at least 3× larger than spot size for accurate measurement.

⚡ Electrical Component Maximum Temperature Limits

Reference values per IEEE, NEMA, and ANSI standards. Use absolute temperature as pass/fail criteria.

Component	Max Temp (°C)	Max Temp (°F)	Standard
INSULATION CLASSES
Class A Insulation	105	221	IEEE/NEMA
Class B Insulation	130	266	IEEE/NEMA
Class F Insulation	155	311	IEEE/NEMA
Class H Insulation	180	356	IEEE/NEMA
CONDUCTORS
Copper bus bar (bare)	70	158	ANSI C37.20
Copper bus bar (insulated)	105	221	ANSI C37.20
Silver-plated connections	105	221	IEEE
Tin-plated connections	90	194	IEEE
SWITCHGEAR
Circuit breaker contacts	70	158	ANSI C37.20
Fuse clips	70	158	UL/ANSI
Molded case breakers	90	194	UL 489
CABLES
THHN/THWN (90°C rated)	90	194	NEC
THW (75°C rated)	75	167	NEC
TW (60°C rated)	60	140	NEC
TRANSFORMERS
Dry-type (Class F)	155	311	IEEE C57.12
Oil-filled (top oil)	105	221	IEEE C57.91
MOTORS
Motor windings (Class B)	130	266	NEMA MG-1
Motor windings (Class F)	155	311	NEMA MG-1
Motor frame surface	90-100	194-212	Typical

Temperature Rise vs Absolute

Maximum temperatures assume 40°C ambient. For higher ambient, reduce maximum allowable temperatures accordingly.

🔍 Common Electrical Thermal Anomalies

Thermal Pattern	Likely Cause	Root Cause	Action
One phase hot (3-phase)	Loose connection	High resistance joint	Re-torque or replace
Two phases hot	Load unbalance	Uneven loading	Balance loads
All phases equally hot	Overload	Excessive current	Reduce load or upsize
Hot fuse/breaker	Poor contact or overload	Worn contacts	Replace
Hot cable splice	Poor workmanship	Inadequate connection	Redo splice
Motor hot spot	Bearing or winding issue	Friction or insulation	Inspect
Transformer hot spot	Cooling or internal fault	Blocked cooling	Clean, inspect
Capacitor hot	Internal failure	Dielectric breakdown	Replace

⚙️ Bearing Temperature Guidelines

Condition	Surface Temp	ΔT vs Motor	Action
Normal	<70°C (158°F)	<10°C	Continue monitoring
Elevated	70-85°C	10-20°C	Check lubrication
High	85-100°C	20-35°C	Schedule inspection
Critical	>100°C (212°F)	>35°C	Immediate action

Bearing Inspection Notes

Compare inboard vs outboard bearings
Max temp limited by lubricant (80-120°C)
Surface temp is lower than internal
Recently greased bearings run warmer

🔌 Motor Surface Temperature

Insulation Class	Max Winding	Typical Surface
Class A	105°C	75-85°C
Class B	130°C	90-100°C
Class F	155°C	105-115°C
Class H	180°C	120-130°C

Surface temperature is typically 20-40°C lower than internal winding temperature.

⚠️ Motor Thermal Patterns

Uniform heating: Overload or cooling problem
One end hot: Bearing issue
Hot spot on frame: Rotor/stator problem
Hot feet: Alignment or soft foot

🏭 Mechanical Equipment Temperature Guidelines

Equipment	Normal	Warning	Critical	Notes
Rolling element bearings	<70°C	70-85°C	>100°C	Limited by lubricant
Sleeve bearings	<60°C	60-75°C	>90°C	Oil film critical
Gearbox (splash lubed)	<80°C	80-95°C	>110°C	Oil temp dependent
Gearbox (force lubed)	<65°C	65-80°C	>95°C	Check oil cooler
Hydraulic system	<60°C	60-70°C	>82°C	Oil degrades faster
Belt drives (belt surface)	<50°C	50-65°C	>80°C	Tension/alignment
Couplings	<45°C	45-65°C	>80°C	Misalignment indicator
Steam traps (downstream)	<100°C	100-150°C	=Steam temp	High = failed open
Pump packing/seal	<80°C	80-95°C	>110°C	May need adjustment
Conveyor bearings	<60°C	60-75°C	>90°C	Often poor lubrication

Mechanical Inspection Tips

Compare similar equipment under similar loads
Account for environmental factors (sun, wind)
Establish baselines during normal operation
IR complements - doesn't replace - vibration analysis

✅ Pre-Inspection Checklist

☐ Equipment at normal operating load (>40%)
☐ Equipment energized for minimum 2 hours
☐ Camera thermally stabilized (15+ min on)
☐ Ambient temperature recorded
☐ Wind conditions noted (outdoor)
☐ Emissivity set correctly
☐ Reflected temperature measured and set
☐ PPE appropriate for arc flash hazard
☐ Safe distance maintained
☐ Previous reports reviewed for baselines

⚠️ Common Mistakes to Avoid

Mistake	Result	Solution
Wrong emissivity	Major temp errors	Verify material, use tape
Target too small	Averaged/low reading	Get closer or telephoto
Reflections	False hot spots	Change angle, add tape
Low load inspection	Missed problems	Inspect at >40% load
Camera not stabilized	Drift in readings	Allow 15+ min warm-up
Ignoring wind	False normal readings	Note conditions
Not focusing	Wrong temps	Always focus first
Solar loading	False hot spots	Inspect shaded side

📋 Report Documentation (NFPA 70B)

Per NFPA 70B 2023, reports should include:

Date, time, and location of inspection
Thermographer name and certification
Camera make, model, serial number
Ambient temperature and conditions
Equipment identification and location
Load conditions at time of inspection
Thermal image (thermogram) of anomaly
Visual image for reference
Temperature of exception and reference
Delta T value and reference used
Severity classification/priority
Recommended corrective action
Emissivity and reflected temp settings

📚 Applicable Standards

Standard	Title/Scope
NFPA 70B	Electrical Equipment Maintenance
NFPA 70E	Electrical Safety in the Workplace
NETA MTS	Maintenance Testing Specifications
NETA ATS	Acceptance Testing Specifications
ASTM E1934	Guide for Examining Equipment with IR
ASTM E1933	Measuring/Compensating for Emissivity
ISO 18434-1	Thermography General Procedures
IEEE C37.20	Switchgear Temperature Limits

Certification Programs

ASNT - Level I, II, III
Infraspection Institute - Certified Infrared Thermographer®
ITC - Infrared Training Center Levels