Combiner box anomaly
Abnormal heating in or around a DC combiner box — typically a high-resistance termination or a failing protection device carrying the combined current of many strings. Treated as a safety-critical finding.
Thermal signature
A localised hot signature at combiner or enclosure positions rather than on module glass: a warm lug, breaker or fuse-holder position standing out against the enclosure, or the enclosure body itself reading well above its surroundings.
Typical ΔT
10–40 °C or more at the affected termination. Because combiner faults sit on high-current aggregation points, they are escalated to the safety class at lower ΔT than module-level findings (typical industry interpretation aligned with IEC TS 62446-3).
What causes it
- Loose or under-torqued lugs and busbar terminations
- Corroded or thermally cycled connections
- Failing breakers, fuse holders or DC disconnects
- String imbalance overloading individual inputs
Power impact
A combiner failure can take every connected string offline at once, and the failure mode — arcing at a high-current DC termination — is a genuine fire hazard. The exposure is measured in whole blocks of the site, not single modules.
Recommended action
Fix: immediate
Act immediately. Have a qualified electrician inspect the combiner: thermographic confirmation at close range, torque check on all terminations, and replacement of any heat-damaged devices. Follow site procedures for working on or isolating live DC aggregation equipment.
Frequently asked questions
Why do combiner findings outrank most module findings?
Current and consequence. A combiner aggregates the output of many strings, so a single failing termination carries far more current than any module connection, and its failure can drop or endanger a whole block of the array rather than one panel.
Can aerial thermography really see inside a combiner box?
Not through a closed metal enclosure — what it sees is abnormal external heating of the enclosure or exposed terminations, which is itself a red flag. The aerial finding is a trigger for a close-range inspection with the enclosure opened by an electrician, not a substitute for one.
Related anomalies
Suspect combiner box anomaly on your site?
Fly the site, upload the thermal frames, and get every module graded against this taxonomy — severity-ranked, with flagged imagery and per-module locations. Quote your site size in seconds.
ΔT figures and abnormality classes on this page describe the typical industry interpretation aligned with IEC TS 62446-3 — indicative engineering guidance, not normative text from the specification. Temperature differentials are only meaningful when captured at ≥600 W/m² irradiance (per the TS) and verified on site before repair work.