Basics
Why solar cable size matters: choosing DC and AC cable for your installation
An undersized cable will not fail on day one. It just quietly costs the system energy, month after month, in a way that is easy to miss until someone finally checks the numbers.
Cable sizing gets less attention than it deserves, mostly because getting it wrong does not cause an obvious, immediate failure the way an undersized breaker does. Instead, it shows up as a small, ongoing loss that is easy to overlook. Here is what actually decides the right cable size for a solar job.
The two numbers that matter
Cable size depends on two things: the current it needs to carry, and the length of the run. Current comes from your string or load rating, which you already know from the system design. Length is the actual physical distance the cable travels, panel to DCDB, inverter to ACDB, or ACDB to the grid connection point, not the straight line distance but the real routed path including any bends.
A longer run loses more voltage for a given cable size, because resistance increases with length. This is called voltage drop, and it is the main reason a cable that works fine on a short run can be genuinely undersized on a longer one, even carrying the exact same current.
Why voltage drop matters in practice
Every bit of voltage lost along the cable run is energy the system generated but never actually delivered. On a badly undersized long run, that loss can add up to a meaningful percentage of total output over a year, essentially money left on the table because of a cable choice made once at installation and then never revisited. Keeping voltage drop within a reasonable range, generally under about 3 percent for the DC side, is the practical target most installers work to.
DC cable versus AC cable
DC solar cable, used between the panels and the DCDB, is built with UV and weather resistant insulation since it usually runs exposed on a rooftop or structure for the system's entire life. AC power cable, used from the inverter to the ACDB and onward to the load or grid connection, does not need the same UV rating if it is routed indoors or in conduit, though outdoor AC runs should still use weather rated cable.
A practical way to get it right
Rather than guessing at a size, the reliable approach is to give your supplier the actual numbers: the current the cable will carry, the DC or AC voltage, and the real run length. From those three figures, a correct size can be confirmed rather than assumed, and it takes a supplier who works with this daily only a few minutes to check.
Send us your current rating, voltage and approximate run length through the contact page or on WhatsApp, and we will recommend a cable size before you place the order.