Solar Lattice

FailureMode

Junction Box Interconnection Failure

ID
fm:junction-box-interconnection-failure
IRI
https://solarlattice.org/kb/fm/junction-box-interconnection-failure
Status
active
Also known as
PVFS 1-14
Category
Modules

This failure is a bad connection inside the module junction box. Solder joints, wires, bypass diodes or tabbing ribbons can be disconnected, broken, burned, corroded or shorted. Typical causes are cold solder joints, residues on the joints, clamps or screws loosened by thermal cycling, and moisture getting into damaged boxes and corroding the contacts. Delamination that loosens the box can also break the contacts. Look for yellowed, browned, burned or bubbled potting, and for burn marks or discoloration behind and around the box. The fault itself may only be visible after the potting is removed. An IR camera shows the box as a hot spot. IV curves or open-circuit voltage measurements can confirm shorts, and the module may lose power or lose its protection against shading. Arcing in the box can start a fire, so treat any burn evidence as a safety issue and isolate the module first. Replace the module rather than repair the box, because repairs can easily lead to new fires. Good sealing of the junction box helps prevent the fault.

Claims

affects

c1 drafted · lead Junction box

c2 verified · fact Bypass diode

Faulty parts in the box can include bypass diodes or the connections to them.

verified by: joshuahamsaverified on: 2026-10-20

c3 drafted · lead Cell interconnect ribbon

Tabbing ribbons inside the junction box can be involved.

caused_by

c4 drafted · lead Solder bond defect

Cold solder joints from low soldering temperature, or chemical residues on the joints.

c5 drafted · lead Manufacturing defect

Chemical residues left on solder joints by the earlier production process.

c6 drafted · lead Thermal cycling

Day-night and seasonal cycles loosen mechanical clamped or screwed contacts.

c7 drafted · lead Moisture exposure

Water gets into bad or damaged boxes (adhesion loss, cracks, missing seal) and corrodes the contacts.

c8 verified · fact Delamination

Delamination near the box can loosen it, which puts mechanical stress on the internal contacts and breaks them.

verified by: joshuahamsaverified on: 2026-10-20

c9 verified · fact Mechanical stress

A loosened junction box puts stress on its internal contacts.

verified by: joshuahamsaverified on: 2026-10-20

c10 drafted · lead Junction Box Failure

In the worst case, junction box failures result in short-circuited or open-circuited module or cell strings.

review note: support check: partial - u14 says junction box failures cause interconnection failure in the worst case, but this reverses the direction, since the interconnection failure is the subject, not an effect of the box failure as a cause.

presents_as

c11 drafted · lead Corroded contacts

c12 drafted · lead Burn marks

Resistive heating can burn the encapsulant or backsheet behind and around the box.

c13 drafted · lead Yellow to brown discoloration

Potting material, encapsulant or backsheet can yellow or brown from heat.

review note: support check: partial - The potting material is said to appear yellowed/browned from heat, but the encapsulant or backsheet is described only as discoloured, not specifically yellow or brown.

c14 drafted · lead Hotspot in IR image

c15 drafted · lead Open string circuit

Depends on whether the bad contact is resistive, open, shorted or arcing.

review note: support check: partial - Open circuit is mentioned as one possible character depending on the contact, but an open string circuit is not a firmly stated symptom.

leads_to

c16 drafted · lead Glass Breakage

c17 verified · fact Arc fault

Internal arcing in the box can start a fire.

verified by: joshuahamsaverified on: 2026-10-20

detected_by

c18 drafted · lead Infrared thermography

c19 drafted · lead Electroluminescence imaging

c20 drafted · lead Visual inspection

c21 verified · fact IV curve tracing

verified by: joshuahamsaverified on: 2026-10-20

c22 drafted · lead Open-circuit voltage measurement

Shorts can be found with an open-circuit measurement.

c23 drafted · lead Junction box inspection

The fault may be hidden under potting material and only show once the potting is removed.

mitigated_by

c24 drafted · lead Module replacement

Repairing junction boxes can easily cause new fires.

c25 drafted · lead Proper junction box sealing

c26 drafted · lead Safety isolation

Give priority to isolation when there is evidence of arcing or burning.

review note: support check: partial - u10 advises prioritizing safety isolation for arcing or burn evidence, but it concerns junction-box failures generally rather than this interconnection failure specifically.

Data