Connectors on the DC side of photovoltaic systems are among the most safety-critical components of a PV installation. They connect modules, strings, and other system components and must reliably transmit electrical energy over many years. Faulty or improperly installed connectors can lead to power losses, system failures, or, in the worst case, fires.

Despite their importance, risks related to DC connectors are often underestimated in practical installations.

Standards and Technical Framework

Connectors used in photovoltaic systems are governed by the international standard IEC 62852 (“Connectors for DC application in photovoltaic systems – Safety requirements and tests”).
With Amendment A1 (2020), additional requirements for safety, electrical load capability, and testing procedures were introduced.

The standard defines, among other things:

• electrical and mechanical testing
• current and voltage ratings
• thermal behavior
• resistance to environmental influences

For practical application, this means: only tested and certified connectors may be used, and they must be installed strictly in accordance with the manufacturer’s specifications.

Manufacturer Instructions as a Mandatory Basis

Connector and module manufacturers provide assembly and installation instructions. These typically specify:

• approved connector types
• requirements for crimp connections
• approved crimping tools
• stripping lengths
• conductor cross-sections and permissible rated currents

These instructions must be followed without exception. Deviations can result in connectors no longer meeting their intended safety and performance characteristics.

Why Connectors Are Especially Critical Today

Due to larger cells, higher module power ratings, and new module designs, module and string currents have increased significantly in recent years. As a result, the contact resistance of connectors has become increasingly important.

Even small deviations from the intended condition can, under high currents, lead to:

• localized heating
• accelerated material aging
• deformation or melting of plastics
• arcing
• fire hazards

Since connectors are typically permanent electrical connections, consistently high connection quality is essential for system safety and long-term operation.

Potential Hazards and Risks

Mismatch of Connector Types (Cross-Mating)

Cross-mating, i.e. connecting plugs and sockets from different manufacturers, is one of the most common failure modes observed in the field.

Even if connectors from different manufacturers can be mechanically connected, the following applies:

• the connection is not tested
• it no longer corresponds to the original certification
• it cannot be considered a reliable connector

In practice, this can lead to increased contact resistance, thermal overload, power losses, or failures. As contact resistance rises, contact points may heat up, causing plastics to soften or melt. This can promote arcing and represents a significant fire risk.

Cross-mating must therefore be strictly avoided.

Faulty Crimp Connections

Crimp connections are a core element of PV connectors. Faulty crimps commonly result from:

• unsuitable or non-approved crimping tools
• insufficient or excessive crimp force
• incorrect stripping lengths
• improperly positioned conductors
• crushed insulation or damaged strands

Typical consequences include increased contact resistance, reduced current-carrying capacity, localized heating, short circuits, or mechanical weakening of the connection up to cable breakage.

A faulty crimp connection is generally not reliably durable. To ensure a safe electrical connection, the connector must be re-terminated correctly. Manufacturer specifications regarding stripping length, conductor positioning, crimp geometry, and tool selection must be strictly observed.

Many manufacturers also explicitly prohibit cutting off and re-terminating connectors.

Incorrectly Installed Cable Entries and Strain Reliefs

In addition to the electrical connection, mechanical installation is also critical.
Missing or insufficient strain reliefs and incorrectly installed cable entries can cause mechanical forces to act directly on the contact area.

This may result in loosened contacts, damaged contact surfaces, or increased contact resistance. Corresponding requirements are specified in manufacturer installation instructions and must be complied with.

Contaminated Connectors

Photovoltaic systems are installed in the field and are often exposed to dust, moisture, and weather conditions. If connectors are left open for extended periods, dirt, moisture, or corrosion can form on the contact surfaces.

When such connectors are later mated, this can lead to accelerated aging, increased contact resistance, and, in extreme cases, thermal damage or fires. Connectors should therefore be kept clean and connected as soon as possible after opening.

Summary

Connectors in photovoltaic systems are a key safety topic. Errors in selection, installation, or combination can pose significant risks to systems, buildings, and people, including consequential damage such as energy yield losses or system downtime.

To ensure safe operation, installers should pay particular attention to:

• strictly following manufacturer instructions and installation guidelines
• using only tested and certified connectors
• consistently avoiding cross-mating
• avoiding open connectors in the field
• using appropriate tools and proper crimping techniques

Careful handling of connectors makes a substantial contribution to the safety and reliability of photovoltaic systems.