How should thermography results be compared from one annual survey to the next?

Compare like with like: the same equipment references, the same measurement points and a recorded load for every image. Then a finding can be tracked year on year as a measured temperature, a difference in °C from a matching reference, and the load at the time. Repaired items should be re-imaged and closed out, not carried forward.

Why raw temperatures don’t compare on their own

A connection’s temperature depends on the current flowing through it and the conditions around it. A board surveyed at a light load one year and a heavy load the next can look worse without anything having changed, or better while a joint is deteriorating.

So every image needs the load recorded with it, and every finding needs a reference: a matching phase or a similar component under the same load. The useful number is the difference in °C between the two, read alongside the load. Where anyone estimates what a reading would be at a different load, that figure should be labelled as an estimate and shown next to the measured value, never in place of it.

Use the same equipment references every year

Year-on-year comparison falls apart when one report says ‘DB-3’ and the next says ‘second floor riser board’. We use the site’s own board, way and tap-off references, and work from the site’s asset list. The first survey, ideally the commissioning survey on a new installation, sets that list.

Anything that could not be opened or imaged is recorded with the reason. Next year, that list is the first thing to check, because a board missed two years running is a gap in the record.

Close out last year’s findings

Each annual report should start by going back through the previous one. Every earlier finding ends up in one of three places:

Repaired and re-imaged: the electrician’s work is recorded and a new image under load confirms the change.
Still present: the new reading, load and °C difference sit next to last year’s, so the change is visible.
Not accessible: the reason is recorded, so it doesn’t quietly drop off the list.

We cover what happens between finding and fix in what happens after a survey finds a hot connection.

What a trend tells you, and what it doesn’t

A difference in °C that grows at the same point, under similar load, is a reason to have it investigated sooner. A thermal image shows where heat is and how much; it does not show why. The cause is for the site’s electrician to find when the cover is off and the circuit is safe to work on. Ti inspects and reports; we do not carry out repairs.

Start with a good baseline

On a new installation, the commissioning survey is the first page of the record. On one London data centre build, 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 one located by its reference. Once put right and re-imaged, that record becomes the baseline every annual survey is compared against. See commissioning thermography vs the annual survey and thermography evidence for the handover pack.

Frequently asked questions

Do we need the same thermographer every year?

No, but the method and references should stay the same, and the report should show the load, the reference point and the measurement position for each finding so anyone can repeat it.

What if the load is much lower this year?

The report should say so and state where that limits the comparison. If a finding matters, a re-image at a higher load may be worth planning.

Can you work from another provider’s previous report?

Yes, if it carries equipment references, loads and images. We map our findings to its references so the history carries on.