Fire Risks from the DC Solar Connector
A PV solar panel has a pair of electrical cables, each with a push-fit DC connector on the end, This allows panels to be easily connected to form an electrical circuit. When pushed together, the DC connectors form a waterproof (IP65, IP68) connection that cannot be pulled apart due to snap-in locking tabs.
Research on solar fires has found the DC connector to be a leading point of fire risk in solar installations. Solar installers are making millions of these connections every year – sometimes in bad weather and awkward locations, increasing the risk of connection errors.
How Solar Connectors Fail
Simple errors in the assembly of DC solar connectors lead to a fault condition which may become an arc-fault with the risk of a fire. Typical errors include:
- Incomplete insertion
- Errors assembling connectors to cables
- Assembling electrodes while wet or leaving connectors in a place where water can pool
- Cross-mating connectors from different manufacturers
- Damage to connectors either during or after installation
| Example | Connector Fault | Panel Connectors | Site-Made Connections |
|---|---|---|---|
 | Not fully engaged, cable under tension |  | |
 | Assembled wet - with potential for corrosion | | |
 | Damage - post or pre-installation | | |
 | Cross-mated connectors |  | |
 | Poor quality assembly and crimp | | |
Incomplete Connection of DC Connectors
If the solar DC connectors are pushed together far enough to make an electrical connection, but not far enough to lock together on the locking tabs, tension on the DC cable could cause the connectors to pull apart and create a gap across which electricity can arc.
Poorly Crimped or Assembled Connectors
The connectors that come pre-attached to the solar PV panel are joined onto the cable in highly controlled factory conditions, so the risk of a poorly made joint is significantly reduced for these connectors.
Cables often need to be added to the circuit to bridge longer distances, such as between panel rows or from the first and last panels in the circuit to the solar inverter. To make up these longer cables, connectors are assembled onto the ends by the solar installer.
A well-trained operative using the correct tools can make this electrical connection in a way that will be safe for the lifetime of the installation. However, using improper tools or a lack of training can result in connections that are loose or prone to corrosion, eventually leading to dangerous arcing.
Corrosion in DC Connectors
If the connector is assembled wet or left in a location where water may pool around the connector, there is an increased risk of corrosion of the metal contacts inside the connector, which introduces additional problems.
Electrical conductivity is reduced by corrosion and as resistance increases, the operating temperature of the connector rises. This can reach a temperature that can melt the plastic housing, causing the connector to come apart with the risk of a gap forming between the contacts resulting in a high temperature arc.
Cross-Mated Solar DC Connectors
Despite its size and importance, the solar industry has not yet created an agreed standard for the DC connectors it uses. The original MC4 connector is the intellectual property of Staubli International AG, but numerous other manufacturers offer so-called ‘MC4 compatible’ connectors.
These are physically interoperable – connectors from different manufacturers can be pushed together to create an electrical connection. Questions, however, remain over the long-term integrity of connections made up of two differing halves. Consequently, regulators in many countries now require that mated plugs and sockets are ‘of the same model and from the same manufacturer’.
So long as the panel manufacturer is only using one single supplier of connectors, they may not, and the solar installer is using only one make and model of panel in the installation, then the short connections between panels should be of the same make and model.
Best practice - Avoiding Cross-Mating
But what happens when cables need to be added to the circuit to connect over longer distances, such as between panel rows or from the panels to the inverter? Many factory-fitted connectors on the PV panels are from a manufacturer that cannot be sourced locally or simply cannot be identified by the installer.
In this case, to comply with regulations against cross-mating, the installer should cut off the factory-fitted connector, creating the requirement to assemble more connectors by hand with the increased risk that poses.
The concern in this situation is that this will void the panel warranty, so the risk is that the installer ignores best practice and regulations. The result is that cross-mated connections become part of the installation.
Correctly Paired or Cross-Mated - Can You Tell the Difference?
Identifying cross-mated connectors isn’t easy. The photo at the top of the page shows correctly paired DC connectors, but this photo shows a mixture of correctly paired and incorrect cross-mated connectors. Can you tell the difference?