Solar cable or Photovoltaic (PV) cable is designed to connect solar panels into an array connected to the PV solar system. The cable is flexible yet moisture-resistant, Ozone, UV, and flame resistant. These cables should last for the lifetime of the solar panel installation and, as such, be made from copper wire strands covered by at least two layers of plastic covering.
The solar cable should only be joined by MC-4 connectors, and the solar cable ends must be crimped to the correct size terminal connectors using a hydraulic crimping tool and zinc-based antioxidant paste on the cable end before crimping. A heat shrink sleeve should be fused over the connection.
It has been proven that a properly crimped MC-4 connection is superior to a soldered connection. The solar cable connection must be:
- Moisture resistant
- Resistant to oxidation
- Flame resistant
- Ozone resistant
- Ultraviolet resistant
Solar cables and connections to the solar panel array need to withstand the onslaught of nature for a minimum of thirty years, the expected lifetime of the solar panels. Let’s look at why solar cable joints should be minimized and be made to last for at least thirty years.
Why Soldering Pigtail Joints On Solar Cable Is Not Good
Planning the wiring diagram of your solar array minimizes the number of cable connections to as few as possible. You will have two connections on each solar panel, a positive and a negative lead.
Depending on whether you will connect the panels in series or parallel, each solar panel should have no more than four connections on either end of the two connecting cables.
You should avoid splicing solar cables together to extend the cable length. The best practice is to cut each cable to length with no joints and only MC-4 type connectors at the cable end.
The efficiency of Soldered Cable
The efficient transport of electrons from the solar panels to the solar charge controller requires quality copper wire of sufficient thickness to reduce resistance to a minimum. All connections between the solar panel and the charge controller are points of potential voltage loss.
- Stranded copper wire is the most commercially viable type of wire with low resistance and the flexibility required to route the wire around tight corners.
- Two lengths of solar cable can be spliced together with a copper crimp connection and sealed with two layers of heat-shrink sleeves, but this should be avoided if possible.
A normal pigtail joint used on indoor wire connections is unsuitable for joining solar cable ends. The joint must be mechanically crimped and sealed with antioxidant grease and then sealed to prevent oxidation or moisture ingress.
How To Solder A Connection Joint On A Length Of PV Cable
The solar power industry has developed an ideal connector to join all solar cables to the solar panels and other branching points. These connectors are known as MC-4 connectors. The connector has a male and female end connected via internal metal joints crimped and soldered to the solar cable ends.
Once connected, the MC-4 male and female ends are sealed against oxygen and moisture ingress. The MC-4 connector is made of UV and Ozone resistant plastic that will last in outdoor applications for more than thirty years.
If you are out of MC-4 connectors and need to make a solar cable connection between two cable ends, you can make use of the following as a temporary solution.
What You Need to Solder
- Straight copper cable connector
- Crimping tool
- Cable Stripping tool
- Silver solder wire
- Soldering iron
- Dielectric grease
- Heat shrink sleeves x 2 pieces (one short, one longer)
Steps To Solder PV Cables
- Strip the protective sleeve from both cable ends, allowing a sufficient length to fit halfway into the copper cable connector. Insert the exposed stranded copper solar wire halfway into one end of the cable connector and securely crimp the cable connector over the wire end.
- Place the heat shrink sleeves over the solar cable and, first, the long sleeve and then the short sleeve. Now repeat the crimping connection to the other end of the solar cable. Use the soldering iron and silver solder to sweat some silver solder onto the joint.
- Allow the joint to cool down completely, and then apply some dielectric grease to the joint and slide the short sleeve over the joint, completely covering the copper cable connector and at least half an inch on either side of the joint. Use a heat gun to shrink and seal the joint.
- Allow the first heat shrink sleeve to cool down before sliding the longer sleeve over the first one and heat shrinking it in place. You should use a different color heat shrink sleeve to indicate the position of the joint.
- This joint will be secure and may last you for some time, but it is not guaranteed to last for 30 years, as with MC-4 connectors.
Looking for poor or broken connections during the system’s life should be avoided by exclusively using MC-4 connectors to wire up the solar array.
How To Make An MC-4 Connection On A Length Of PV Cable
MC-4 connectors have become the norm for making connections on solar cables. Solar panels can be connected in parallel or in series, or two arrays can be joined together before being connected to the solar charge controller.
MC-4 connectors come in various configurations to allow for connecting solar cables inline or in branch configurations required for parallel connections. Most commercial solar panels are already fitted with MC-4 connectors on the wire terminal ends.
An MC-4 connector consists of a plastic male and female junction that fit together to present a completely sealed and weatherproof coupling. The female plastic end contains a male metal connector inside the plastic housing.
The stripped solar cable end is inserted into this male metal connector and mechanically crimped onto the metal connector. The mechanical bond is strong enough, but many installers also sweat some silver solder onto the crimped wire to eliminate any oxygen in the joint.
Dielectric Antioxidant Grease
Some dielectric antioxidant grease is then applied to the joint. The male metal connector is then assembled into the female plastic housing, forming an airtight seal around the cable end.
Male and Female Connections
The same joining process is followed on the other end of the cable using the plastic male MC-4 housing and the metal female connector. The male and female plastic connectors can now be joined, and it will make an audible click when the two ends are properly connected.
National Electric Code
MC-4 connectors are certified by Underwriters Laboratory (UL) and comply with the National Electric Code (NEC). The locking mechanism of the MC-4 connectors will ensure that the solar cable ends will not become loose.
The plastic used for the MC-4 connectors is UV stabilized and Ozone resistant and will last in outdoor installations for more than thirty years. MC-4 connectors can be sold as single connections or branch sets.
Special tools to tighten the MC-4 connectors, seal ends, and unlock the male and female joints can be bought separately.
