What is ΔT in thermography?

ΔT (delta T) is the temperature difference between the measured component and a reference point (typically a similar component under the same load, or ambient temperature). It is the primary severity indicator in thermographic inspections.

What severity levels are used?

Common severity classification uses four levels: Minor (monitor), Intermediate (plan repair), Serious (repair soon), and Critical (immediate action). The ΔT thresholds vary by component type and industry standards.

What ΔT thresholds apply to electrical panels?

For electrical connections (ΔT over ambient): 1-10°C = Minor, 11-20°C = Intermediate, 21-40°C = Serious, >40°C = Critical. These thresholds are based on NETA MTS standards and are widely used in electrical thermography.

How does load affect thermography readings?

Temperature rise is approximately proportional to the square of the current (I²R heating). When equipment is not at full load, findings may be worse at full load. Always record the load percentage during inspection and extrapolate to full load conditions.

What are the main standards for thermography?

Key standards include ISO 18434 (condition monitoring by thermography), NETA MTS (electrical maintenance testing), ASTM E1934 (IR building surveys), and IEC 62446 (PV systems). ISO 18434 provides the overall framework for machine condition monitoring using IR.

Free Engineering Tool

Thermography Temperature Limits

Classify infrared inspection findings per ISO 18434. Enter component type and measured ΔT above reference to get severity classification and recommended action.

ISO 18434NETA MTSIR Inspection

Classification

Severity

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Measured ΔT

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Priority

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Recommended Action

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Temperature Thresholds for This Component

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Temperature Gauge

Electrical Components (NETA MTS, ΔT over ambient)

ΔT (°C)	Severity	Priority	Action
1–10	Minor	4	Monitor, repair at convenience
11–20	Intermediate	3	Plan repair at next scheduled outage
21–40	Serious	2	Repair as soon as possible
>40	Critical	1	Immediate action — risk of failure/fire

Mechanical Components

Component	Minor	Intermediate	Serious	Critical
Motor body	<10°C	10–25°C	25–40°C	>40°C
Bearing housing	<10°C	10–20°C	20–35°C	>35°C
Coupling	<5°C	5–15°C	15–25°C	>25°C
Steam trap	<20°C	20–40°C	40–60°C	>60°C
Insulation	<5°C	5–15°C	15–30°C	>30°C