185 microhms on a busbar joint. Thermography showed nothing at that point — no temperature differential, surface contact looked stable. Standard IR review would have passed it.

At rated load on a busbar of that rating, 185 μΩ of contact resistance dissipates several kilowatts of heat continuously at that joint. Thermography would eventually have detected it — but not pre-energisation, and not before load had been applied. Ductor testing identified the value immediately. A polarity check then indicated reversed installation. Re-assembled correctly, the joint measured 22 μΩ.

The resolution took approximately an hour before energisation. The scenario that follows from powering up a reversed busbar joint at rated current has a different cost profile.

Pre- vs post-energisation intervention

A contact resistance fault identified pre-energisation is a mechanical correction — reassembly, re-torque, re-test, documentation update. Identified post-energisation under load, the same fault is a thermal event unfolding in a live system, with all that follows from unplanned outage, remediation scope, delay penalties, and potential equipment damage.

~1 hr
pre-energisation correction
EUR2-5M
post-energisation exposure

The limitation of thermography as a standalone method

Thermography is a necessary part of the verification picture — it's not a sufficient one. It identifies conditions that are already generating heat. Pre-energisation reviews take place at low or zero load. At that point, a resistance fault at a busbar joint is invisible to a thermal camera because the thermal signature hasn't developed yet. The fault is present. It just doesn't present visually until load is applied.

Ductor testing measures contact resistance directly, at the joint, independently of load conditions. It identifies the fault before it becomes a thermal event. Polarity verification identifies installation errors — reversed joint orientation, incorrect phasing — that thermography has no mechanism to detect at any load level.

Commissioning workflows that rely on IR as the primary or sole method of joint verification are working within a detection blind spot. The joint in this case would have passed an IR-only review without a flag. The ductor reading and polarity check are what brought it to light.

What the review is looking for: Ductor results for every busbar joint, not just those that appear suspicious on visual or IR review. A threshold of under 25 μΩ per joint is the commonly applied reference for new installations — values above this warrant investigation before energisation. Polarity check records should be present for all joints in the assembly.

When the finding matters

The window for cost-effective resolution is pre-energisation. That's when a 185 μΩ reading is a maintenance task. Once the system is live under load, the same finding is an operational incident. Independent pre-energisation review with ductor and polarity coverage is what creates that window. A commissioning process limited to IR doesn't.