When should an electric bus depot have its electrical thermography survey?

During the overnight charging window, when most of the fleet is plugged in and the depot’s supplies carry their heaviest load. A daytime survey, with buses out on the road, sees charger supplies running at a fraction of that. The survey covers the intake, main switchboard, charger feeders and the AC side of each charger, plus workshop and depot boards.

Why timing decides the result

Thermography shows heat at connections carrying current. In a bus depot the big electrical load arrives when the buses do: in the evening, as vehicles return and chargers start, through to the early morning. By mid-morning most of the fleet is out and the charger feeders are lightly loaded. A survey booked for normal office hours will mostly image cables carrying very little, so the readings tell the operator little about how the supplies behave when it matters (see what load a survey needs).

What should be in scope

The intake and main LV switchboard, including any new section added for charging.
Charger feeder boards and the cables to each charger or charger cabinet, imaged on the AC side.
Depot and workshop boards: lighting, wash plant, compressors, pits and lifts.
Offices, control room and canteen distribution.

The vehicles themselves, their batteries and any DC charging components are outside an electrical distribution survey and are scoped separately with the charger supplier. The same applies to the AC side of battery storage on site (see EV charger and battery storage supplies).

Planning a night survey

Agree the visit with the depot engineer and the charging schedule, so the thermographer arrives once most of the fleet is plugged in. The depot’s authorised person opens panels; the thermographer records the number of vehicles charging and the load on each feeder at the time. Yard safety matters at night: the visit follows the depot’s own rules on moving vehicles, walkways and high-visibility clothing. Daytime boards, such as workshop and offices, can be imaged at the end of the day shift on the same visit.

New depots and conversions

Many depots are being converted from diesel to electric in stages. Each new block of chargers adds load to an intake and switchboard that may have been in place for years. A survey once a new phase is in full overnight use gives a baseline for the new feeders and shows how the existing switchboard copes with the extra load (see annual PPM electrical thermography).

What the report gives you

A same-day report from Ti Thermal Imaging that locates each finding by board, circuit and phase, with the measured temperature, where it was taken, the difference in °C from a matching reference and the load at the time. Ti inspects and reports; the depot’s electrical contractor investigates with the circuit isolated and carries out any work.

A finding from the busbar stage

Heavy load shows up what light load hides. On a London data centre build, commissioning thermography by our team found 16 busbar sections reading above 80 °C under test load, the highest 103.5 °C at a tap-off unit.

Frequently asked questions

Can the survey be done without stopping charging?

Yes. It is a live survey, so the fleet keeps charging throughout.

Does the same apply to rail or tram depots?

For the depot’s own low-voltage distribution, yes: survey when it is busiest. Traction power systems are scoped separately with the rail operator.

How often should a bus depot be surveyed?

Most sites survey annually, and again after a new phase of chargers comes into full use.