Can generator and ATS changeover panels be thermally imaged live?

Yes, but only part of an ATS or generator changeover panel can be surveyed under normal running. The mains side of the transfer switch carries the building load and can be imaged live. The generator side only carries current when the set is running on load, so it is best surveyed during the site’s planned on-load generator test.

Why the generator side is usually cold

Thermography finds problems by looking at connections while they carry current. In an automatic transfer switch (ATS) or changeover panel, the mains supply feeds the load almost all of the time. The generator incomer, its cables, terminations and the generator-side contacts sit energised but carry little or no current until the set starts and the switch transfers.

Image the panel on a normal day and the generator side will look cool and even. That tells you very little. A loose termination that would heat up within minutes of a real mains failure can look exactly like a sound one when no current flows.

What can be surveyed live, on any day

The mains incomer terminations and cables into the ATS or changeover panel
The mains-side contacts or switching device, where visible with covers opened by the site’s electrician
The common load-side busbars and outgoing terminations
Control supplies, fuses and small wiring inside the panel

These carry the building’s real load, so they can be imaged as part of the normal electrical thermography survey with nothing switched off.

How to survey the generator side properly

Many critical sites already run their standby generators on load at planned intervals, either on a load bank or by transferring the building onto the set. That is the window to image the generator side. We agree the timing with the site team so the thermographer is in the switch room once the set has been carrying load long enough for connections to reach a steady temperature, then image the generator incomer, the generator-side contacts and the terminations at the alternator output box where access is safe.

The report records which side of the switch each image was taken on, whether the load came from the building or a load bank, and the current at the time where the panel or set displays it.

Traps a good thermographer avoids

Heat from the engine. Exhaust, radiators and the engine block are hot by design. Readings are taken on electrical connections and compared like for like, not against the set itself.
Anti-condensation heaters. Many generator and changeover panels have heaters fitted to keep moisture out. They are warm by design and are noted, not reported as findings.
Bare and shiny metal. Busbar and lugs reflect heat from elsewhere. Readings are taken on painted or oxidised surfaces, and any reading on bare metal is noted as a limitation.

Why it is worth the effort

A standby supply is only tested for real when the mains fails. Commissioning work shows how much can hide in a new installation until it carries load: on one London data centre build this autumn, our commissioning thermography recorded 16 busbar sections reading above 80 °C under test load, the highest 103.5 °C at a tap-off unit, each located and imaged before handover. The same principle applies to the generator path. If it never carries current during a survey, it has never really been surveyed.

Ti inspects and reports. The client’s electrical team or contractor investigates any finding with the circuit isolated and carries out the work.

Frequently asked questions

Does the generator need to be run specially for the survey?

Not usually. We time our visit to the site’s existing on-load test so no extra run is needed.

Can the changeover panel be imaged without a shutdown?

Yes. Nothing is switched off for the thermography itself. Covers are opened by the site’s electrician under the site’s own safe system of work.

Should the generator side be surveyed every year?

Many sites include it in the annual electrical thermography survey by booking the visit on a test day. Sites with a critical standby supply, such as data centres and hospitals, may choose to image it at more than one test window a year.