WiremanWireman · Find a hot connection with a thermal camera: troubleshooting for electricians · 2023 NEC ·
Find a hot connection with a thermal camera
Scan under load, compare like with like, and judge how serious a hot spot is.
Before you start
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How it works
A loose or corroded connection has extra resistance, and current through it makes heat (I²R). A thermal camera shows that heat before the connection fails. It doesn’t measure temperature directly; it measures infrared energy coming off a surface, and how much a surface gives off depends on its emissivity. Shiny metal gives off little and reflects a lot, so readings on bare lugs can be badly wrong, while tape, paint and insulation read accurately.
Every question and answer in this guide. Tap “Step by step” to walk through it.
- Is the equipment carrying a good share of its normal load?
- Yes, 40% or moreTest: Scan and compare
- Similar parts all within a few degreesNo problems found
- One spot hotter than matching partsHow much hotter is it than the matching part on the other phases?
- About 1–3 °CSmall difference: investigate and watch
- About 4–15 °CTest: Check whether it’s carrying more currentExpect: Similar current on all of them.
- Similar current, so it’s resistanceHigh-resistance connection
- The hot one carries much more currentHeat from current, not a bad connection
- More than 15 °CMajor hot spot: repair now
- All phases evenly hotTest: Measure current on every conductorExpect: Phases below the rating; neutral current reasonable compared with the phases.
- Within ratingsNo problems found
- At or above the ratingHeat from current, not a bad connection
- Neutral near or above phase currentHarmonic heating
- Light load or mostly offWait for more load
- Yes, 40% or moreTest: Scan and compare