Junction box / terminal

Definition

The junction box connects the panel's internal circuit to the external cables and houses the bypass diodes. When the resistance of a solder joint, terminal or connector contact inside it rises, heat is generated as current flows. The heating is progressive. As the temperature rises, the contact degrades further and the resistance continues to rise.

Signs in the imagery

In the thermal image it shows as a sharply bounded hot area near the edge of the panel where the junction box sits. The heat passes from the back to the front surface. The rest of the panel is usually at normal temperature. Because the junction box is underneath the panel, it is generally not visible in the RGB image.

Possible causes

• A weak solder joint or loose terminal inside the junction box
• Corrosion or moisture ingress at the contacts
• A bypass diode heating up from carrying current continuously
• A badly crimped or mismatched connector

Effect on production and safety

The effect on production is usually small, but in terms of safety it is among the most serious anomalies. The heating can melt the junction box housing, burn the backsheet and lead to arcing. That is why it is listed first among the anomalies that carry fire risk.

Recommended action

Raise a work order immediately and check the junction box, its lid and the connectors in the field. If there is melting, discolouration or burn marks, isolate the panel safely and replace it. Also check panels and connectors in the same string that show similar heating.