Should UPS bypass and maintenance bypass panels be included in a data centre thermography survey?

Yes, but what it can show depends on how the UPS is running. In normal double-conversion operation the static bypass and the external maintenance bypass carry little or no current, so they show no heat. The survey should image the connections that are carrying load, record which path each UPS is on, and list anything not assessed.

Why bypass paths are easy to get wrong

Thermography finds poor connections by the heat they give off when current flows through them. A UPS has more than one route to the load. In double-conversion running the load goes through the rectifier and inverter. The static bypass inside the UPS waits for a fault or overload, and the external maintenance bypass, often a wraparound panel with its own breakers, stays open until someone needs to work on the UPS. A connection on a path that carries no current gives off no extra heat, so a degraded joint there will not show. A clean image of an idle bypass is not a pass, and the report should not count it as one.

What can be imaged in normal running

UPS input (rectifier) supply terminations and the upstream breaker feeding them
UPS output terminations and the output breaker or isolator
The connections in the maintenance bypass panel that sit in the live load path, such as the UPS output and load-side terminations
Output distribution fed from the UPS, through to the critical load boards
Separate bypass input supply cables and terminations, recorded with their load, which may be close to zero

When the bypass path can be assessed

The bypass path can only be assessed while it is carrying load. That happens in two cases. Some UPS systems run in an eco or high-efficiency mode, where the load normally flows through the static bypass; on those sites the bypass is the live path and is imaged like any other loaded connection. The other case is planned maintenance, when the UPS is transferred to maintenance bypass so the engineer can work on it. If that transfer is already planned, the survey can be timed to image the bypass connections once the load has settled. The switching is always done by the site’s authorised person or the UPS maintainer under the site’s own procedures; Ti never operates switchgear or UPS controls.

What the report should say

For each UPS we record the operating mode, which path was carrying the load, and the current on the input, output and bypass where the site’s metering shows it. Anything on an idle path is listed as not thermally assessed, so the gap is visible to the client and their insurer. Each finding carries the measured temperature, where it was taken, the reference it was compared with and the difference in °C. Ti Thermal Imaging inspects and reports; the site’s electrical contractor or UPS maintainer 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 around a UPS: a finding is only useful if it says which unit, which path, which connection and what load.

Frequently asked questions

Should we put the UPS on maintenance bypass just for the survey?

Not for the survey alone. Transferring to bypass removes the UPS’s protection from the load and is a decision for the site’s operations team. If a transfer is already planned, the survey can be timed around it.

Is the inside of the UPS cabinet included?

Connections the site or UPS maintainer can safely expose are imaged under load. Anything behind fixed internal covers is listed as not viewed rather than assumed clear.

How often should the UPS connections be surveyed?

We include them in the annual electrical thermography survey, and recommend an extra look after a major load change or works on the UPS.