Electrical panel thermal imaging: what the scan finds, and how the covers come off safely

01Why panels are scanned under load

Most electrical failures in a panel start at a connection: a lug that was never torqued, a terminal that loosened with years of heating and cooling, a breaker whose contact has worn. Each one adds a little resistance, and resistance carrying current makes heat.

The heat grows faster than the load. At a resistive joint the power turned into heat is the current squared times the resistance, so doubling the current makes four times the heat. That is why a panel is scanned energized and carrying its normal load, and why a connection that looks fine at night can be the hottest thing in the room at the afternoon peak.

A thermal camera shows that heat in seconds, without touching anything. A thermographer then measures it, compares it with identical parts under the same load, and grades how urgent it is. See electrical infrared inspections for how we run a full survey.

02What the camera checks in a panel

With the dead-front off, a thermographer works through the panel from the supply down:

• Main lugs and incoming conductors. Every amp in the panel passes through them, so a poor main termination affects everything downstream.
• Breaker terminals. Each breaker's line and load connections, compared with the breakers beside it.
• Breaker-to-bus connections. Heat at the line end of a breaker can come from a worn or loose connection to the bus behind it.
• Neutral and ground bars. Neutral terminations can carry more current than expected where non-linear loads such as drives, LED lighting and electronics share the panel.
• Conductors and insulation. A conductor that is warm along its whole length points to overload; one that is hottest at its end points to the termination.
• Phase balance. The three phases of a circuit should look alike. One phase hotter than the others, or one noticeably cooler, is worth a clamp-meter reading.
• Fuses and fuse clips in fused panels and disconnects, where tired clip springs heat the fuse ends.
• Starters in motor control centres. Contactor and overload terminals, where one phase running hotter than the other two usually means a loose or corroded connection. The photos below come from MCC buckets.

Our Level II thermographers are also journeyman electricians, so the open panel gets an electrician's eye too: they point out non-thermal problems they see during the scan as well.

03How hot is too hot

A temperature on its own says little. A breaker terminal at 45 °C could be normal in a warm room or a problem beside identical terminals at 25 °C. Findings are graded by temperature difference (ΔT), preferably against a similar component under similar load, and against ambient air only when there is nothing to compare with.

The guidance most electrical thermographers use in North America is NETA's Table 100.18, from the ANSI/NETA Maintenance Testing Specifications:

Summarized from ANSI/NETA MTS Table 100.18. Check the edition your program follows.

Two things change the grade. The first is load: the same loose lug reads very differently at 30% and at 90% of normal load, so the load at the time of the scan belongs in the report.

Where normal load is not possible, NFPA 70B guidance is to scan at no less than 40% of normal circuit loading. The second is criticality: a probable deficiency on the feeder to an operating room or a production line is scheduled sooner than the same reading on a spare circuit.

04Taking the cover off safely

The camera never touches anything. The risk in a panel scan comes earlier, when the dead-front comes off energized equipment.

NFPA 70E, and CSA Z462, Canada's closely aligned workplace electrical safety standard, treat these as two different tasks. NFPA 70E's table for estimating the likelihood of an arc flash (Table 130.5(C)) lists infrared thermography and other non-contact inspections done outside the restricted approach boundary as a task where an arc flash is not likely, and that line expressly excludes opening doors or covers. Opening covers to expose energized parts is listed as a task where an arc flash is likely.

The scan itself is low-risk. Removing the cover is energized electrical work, and it is planned like energized electrical work.

In practice that means:

• Covers are removed and reinstalled by a qualified electrician, ours or yours, under your site's procedure.
• PPE is chosen from the panel's arc flash label or the site's risk assessment, not guessed.
• The thermographer stays outside the restricted approach boundary while scanning.
• Panels that cannot be opened safely while energized are listed in the report as not inspected, with the reason, rather than skipped quietly.

Infrared windows. Switchgear and motor control centres that are scanned often, or that carry high incident energy, can be fitted with infrared inspection windows so the camera sees in without the door opening.

They need planning: a window passes only part of the infrared energy, so the camera has to be set for that window's transmission, and the camera sees only what lines up with the window. We scan through windows where they are installed and say in the report what could not be seen.

No arc flash labels on your gear, or a study more than five years old? See our arc flash studies and the background in understanding arc flash hazards.

05What a panel scan cannot tell you

An infrared scan reads surface temperature under the load of the day. A good report says what that leaves out:

• Whether a breaker will trip. A breaker can run cool for years and still fail to open on a fault. Trip function is proven by circuit breaker testing, usually during a planned shutdown.
• Circuits that were not loaded. A connection with no current through it makes no heat, however loose it is.
• What the camera cannot see. Connections behind barriers, inside breakers or at the back of the bus show only as heat that reaches a visible surface.
• Cold problems. In parallel runs, the failing conductor can be the cool one, because its current has moved to the others. See when the cold spot is the problem.

06After the scan

Anything urgent is reported to your site contact before we leave. The report usually follows within 10 business days, with thermal and visible photos of every finding, the measured temperatures and ΔT, the load at the time, a grade and a repair recommendation.

Then the scan pays for itself in three steps: repair the findings, re-scan the repaired connections under load to confirm the fix, and scan the same labelled panels on a schedule. NFPA 70B-2023 sets a maximum of 12 months between infrared surveys, and 6 months for equipment in poor condition. A terminal that is a few degrees warmer every year is repaired on your schedule instead of failing on its own.

For costs, frequency and what the full report should contain, see our guide to electrical infrared inspections in Canada. If the scan is for an insurer, see infrared inspections for insurance.

07Questions