Mismatched Connectors Are a Common Cause of Safety and Reliability Issues in Solar Installations

DC connector mismatch is all too common in solar photovoltaic (PV) installations and can cause safety and reliability issues. The positive and negative connectors on the leads of a PV module must only connect to connectors of the same type and manufacturer. Mismatched connectors may work at first, but slight differences in dimensions and materials can cause resistance, leading to heat buildup and eventual failed connections.

Unlike USB connectors or common AC plug-and-socket connectors, there is no standard for solar PV connectors. Stäubli’s MC4 connectors dominated the market a decade ago, and many other manufacturers began to release connectors they called “MC4-compatibile.” However, in a union of an MC4 connector and an “MC4-compatible” connector, each connector may have been assessed and listed by a nationally recognized testing laboratory (NRTL) without their joint connection being listed. While a connection that is not listed may function, it may not be reliable long term. Considering the many manufacturers of PV modules, inverters and module level power electronics (MLPE; power optimizers, microinverters, etc.), testing and certifying all combinations of connectors is unlikely.

PV Module Manufacturer Connector (left) and Stäubli MC4 Connector (right)

Although PV connector mismatch is not a new problem — and installation instructions for many modules state that connectors from different manufacturers must not be mated together, as it can result in out-of-warranty repairs should a failure occur — industry trends are increasing its occurrence. On residential and smaller commercial PV systems, MLPE are growing in popularity because they can help modules produce as much power as possible and help alleviate shading issues. However, since this setup requires each module to connect to an MLPE instead of in series to its neighboring panels, there are many more DC connections and many more opportunities for failure should connectors be mismatched.

Power Optimizer MC4 Connector (right) Mated to PV Module Manufacturer Connector (left)

Electrical building codes and standards are addressing the topic more directly. The 2020 National Electrical Code (NEC) added the following to article 690.33(C), “Where mating connectors are not of the identical type and brand, they shall be listed and identified for intermatability, as described in the manufacturer’s instructions.” (Intermatability in this usage can be thought of as interconnection.) North and South Carolina adopted the 2020 NEC as of November 2021 and January 2023, respectively, so a code-compliant solar installation in the Carolinas will not mismatch DC connectors unless the combination is listed for intermatability.