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Electrical thermography severity

Enter the hot spot temperature, a similar component’s temperature, ambient and current to get the repair priority per NETA criteria and the estimated temperature at full load.

Pre-sizing and estimating tool: results do not replace design, calculations or reports signed by a licensed professional, nor verification against the applicable codes and standards.

Check
Component

Suggested by type; confirm with the manufacturer (temperature-rise limits in IEC 61439-1 and UL 489).

Thermogram
Load

Exponent 2 for purely resistive heating; 1.6 to 1.8 compensates for higher heat loss at high temperatures.

Several points? Batch inspection (paste from Excel)

One row per point: name; hot spot temperature; similar component (may be blank); ambient; measured current; rated current. Temperatures in page units. Component type, limit and exponent come from the fields above.

See what was read
—Repair priority (NETA)
—

Measured ΔT against the criteria

NETA priority bands for both criteria; the black bar is the measured value.

Tap the chart to see the values.

Estimated temperature versus load

Rise over ambient corrected with the square of current (or the exponent entered).

Tap the chart to see the values.

The report gathers this page's inputs, results, equations, assumptions and references, with fields for project, engineer and revision. In the print dialog, choose Save as PDF.

Method, assumptions and references

Equations used

ΔT similar = hot spot T − similar component T; ΔT ambient = hot spot T − ambient T
NETA, similar: 1–3 °C priority 4; 4–15 °C priority 3; above 15 °C priority 1
NETA, ambient: 1–10 °C priority 4; 11–20 °C priority 3; 21–40 °C priority 2; above 40 °C priority 1
Load correction: T(load) = T amb + (T measured − T amb) × (load ÷ measured load)ⁿ, n = 2

Assumptions and limits

  • Temperatures already corrected for emissivity and reflected temperature in the camera; shiny metal surfaces need high-emissivity tape or paint.
  • Load correction is an estimate; wind, enclosure closure and convection change the actual temperature.
  • The priority adopted is the more severe of the two criteria.

Standards and technical documents

  • ANSI/NETA MTS-2023: Standard for Maintenance Testing Specifications, Table 100.18 (thermographic survey)
  • NFPA 70B:2023: Standard for Electrical Equipment Maintenance (infrared thermography at least annually)
  • ISO 18434-1:2008: Condition monitoring and diagnostics of machines — Thermography — General procedures
  • ABNT NBR 15572:2013: Ensaios não destrutivos — Termografia — Guia para inspeção de equipamentos elétricos e mecânicos
  • ASTM E1934-99a: Standard guide for examining electrical and mechanical equipment with infrared thermography

U.S. regulations

  • OSHA 29 CFR 1910.333 and NFPA 70E: work on or near energized equipment, arc flash risk assessment and PPE
  • NFPA 70B:2023: electrical maintenance program, adopted by many authorities having jurisdiction and insurers

Frequently asked questions

What ΔT indicates a problem in thermography?

Under NETA criteria, more than 15 °C (27 °F) above a similar component under the same load, or more than 40 °C (72 °F) above ambient, calls for immediate repair. Between 4 °C and 15 °C over the similar component, a deficiency is probable.

Why correct for load?

Heating grows with the square of current. A spot with a 30 °C rise at 50% load can reach a 120 °C rise at full load.

How often should electrical thermography be done?

NFPA 70B:2023 requires at least one survey per year, at the highest practical load. Critical equipment or assets with a failure history call for shorter intervals.