Should power factor correction capacitor banks be included in an electrical thermography survey?

Yes. Power factor correction (PFC) capacitor banks sit on the main LV switchboard and carry current whenever their steps are switched in, so they belong in the same live survey as the switchgear. Image them under load with the steps in service recorded, and compare like with like, because capacitors, reactors and discharge resistors are built to run warm.

Why PFC panels get missed

Many surveys image the main switchboard and the distribution boards and skip the PFC panel beside them. It is often a separate cabinet supplied and serviced by a specialist, and it can look like a box that looks after itself. Inside are fuses, contactors, cable terminations and busbar connections carrying real current, the same kinds of connection a thermographic survey is there to check anywhere else in the building.

What we image in a PFC panel

The incoming supply terminations and the busbar connections inside the panel
Step fuses and fuse holders
Step contactors and their terminals
Capacitor terminals and cable connections
Detuning reactors, where fitted, and their connections
Cooling fans and filters, where heat build-up inside the cabinet is visible

Which steps are in?

A PFC panel switches its capacitor steps in and out as the site load changes. A step that is out when the image is taken carries no current, so a poor connection on it will not show. That is why we record which steps are energised at the time of the survey, alongside the load, and why the survey works best during normal working hours when the site is drawing its usual load. If some steps never switch in during the visit, the report says so, so that nobody reads a clean image of an idle step as a pass.

What runs warm by design

Several parts of a PFC panel are meant to be warm. Detuning reactors run warm in normal service, capacitors give off some heat, and discharge resistors warm up after a step switches out. Shiny busbar and terminal surfaces can also reflect heat from elsewhere in the cabinet. The useful comparison is like with like: one phase against the others on the same step, and one step against the others of the same rating. A connection that stands out from its neighbours under similar load is worth reporting. A reactor that is simply warm, like every other reactor in the bank, usually is not.

What the report gives you

Each finding is located on the panel and step, with the measured temperature, where on the component it was taken, the reference it was compared against and the load at the time. The specialist who maintains the PFC equipment then has something specific to investigate. Ti Thermal Imaging inspects and reports; the PFC specialist or the site’s electrical contractor investigates and carries out any work.

Why measurement detail matters

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. Every one was located and imaged before handover. The same discipline applies to a PFC panel: a figure only helps the person fixing it if it says exactly where it was measured and under what load.

Frequently asked questions

Does the PFC panel need to be switched off for the survey?

No. It is imaged live, with the site’s authorised person opening one cover at a time under the site’s permit system. Switching it off would remove the current the survey needs to see.

Who should open a PFC panel that is under a service contract?

Agree it before the visit with the site’s maintenance team and, where needed, the PFC service provider. Some sites ask the specialist to attend.

How often should the PFC panel be surveyed?

Most sites include it in the annual electrical survey of the main switchboard. The interval is set by the site’s own risk assessment and its insurer.