Should the bus coupler in a 2N data centre switch room be included in a thermography survey?

Yes, with one honest limit. In a 2N switch room the bus coupler is normally open, so its main contacts carry no current and show no heat. The survey should image the busbar and incomer connections on each side under normal load, record the coupler’s position, and image the coupler itself only when planned switching closes it under load.

Why the bus coupler is a special case

Thermography finds poor connections by the heat they give off when current flows through them. In most dual-fed data centre switch rooms the A and B sections run separately and the bus coupler between them stays open in normal running. An open coupler is energised on one or both sides but carries no load current, so a loose or degraded contact inside it gives off no extra heat and will not show on a thermal image. A clean image of an open coupler tells you very little, and a good report says so rather than counting it as a pass.

What can be imaged in normal running

Incomer circuit breaker terminations and cable boxes on each section
Busbar joints and droppers along each section of the switchboard
Outgoing way connections feeding UPS input, mechanical plant and distribution
The incoming connections to the coupler panel, where they carry the section’s current
Generator and changeover connections that are in service at the time

When the coupler can be assessed

The coupler’s own contacts and connections can only be assessed while it is closed and carrying load. That happens during planned maintenance, when one supply is taken out and the coupler is closed to keep the board fed, or during a planned transfer test. If the site has that switching planned, the survey can be timed to image the coupler panel once the load has settled. The switching is always carried out by the site’s authorised person under its own procedures; Ti never operates switchgear.

What the report should say

For every section we record the load at the time of imaging and the position of each coupler and incomer. If the coupler was open, the report states it was open and not thermally assessed, so the gap is visible to the client and their insurer rather than hidden. Each finding carries the measured temperature, where it was taken, the matching reference it was compared with and the difference in °C. Ti Thermal Imaging inspects and reports; the site’s electrical contractor investigates and carries out any work.

Why location 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 in a 2N switch room: a finding is only useful if it says which section, which joint and what load.

Frequently asked questions

Should we close the bus coupler just for the survey?

Not for the survey alone. Switching changes the site’s resilience and is a decision for the site’s operations team. If coupler switching is already planned, the survey can be timed around it.

Is the open coupler still worth looking at?

Yes, for the connections that carry current on the incoming side and for its general condition. The report is clear about what an open coupler can and cannot show.

Does the same apply to standby generator and changeover connections?

Yes. Any connection that is not carrying load on the day cannot be assessed thermally, so its position and load are recorded and the report says what was and was not covered.