Short answer: there is no universal “correct solar cable size.” Cable thickness depends on the circuit. PV strings can run at hundreds of volts and relatively modest current, while a 48V battery feeding a multi-kilowatt inverter can carry well over 100A. Current, distance, voltage drop, installation method, temperature, insulation and fault protection all matter.
Why battery cable gets thick very quickly
At 5kW and 48V, the idealised DC current is already about 104A before inverter losses and transient loads are considered. At 8kW it is about 167A. This is why battery conductors often use large cross-sections and why undersized lugs, fuses and disconnectors become serious safety issues.
PV cable and battery cable solve different problems
| Circuit | Typical characteristic | Main design concern |
|---|---|---|
| PV string | High DC voltage, string-level current | Voltage rating, current, UV/environment, connectors, voltage drop |
| Battery to inverter | Low DC voltage, very high current | Ampacity, voltage drop, short-circuit protection, lug quality, cable length |
| Inverter AC input/output | 230V AC household/commercial current | Breaker coordination, cable installation method, voltage drop |
| Earth conductor | Protective bonding / fault path | Continuity, sizing and installation standard |
| Communication cable | Low-power signal / data | Correct pinout, shielding/termination where required, separation from power cables |
Why distance matters
Voltage drop is roughly proportional to current and conductor resistance. A longer battery cable can therefore require a larger cross-section than a short run carrying the same current. On the low-voltage battery side, even a small voltage drop can materially affect inverter behaviour.
Why two 50mm² cables are not automatically equivalent to “enough”
Cable ratings depend on more than copper area. Flexible battery cable, conduit wiring, trunking, ambient temperature, bundled conductors and insulation type can have different current-carrying capability. The fuse must protect the cable—not merely match the inverter's marketing power.
Deye's battery installation documentation gives a useful example: for a 12kW inverter on a 51.2V battery bank it calculates a minimum continuous current requirement around 240A and warns that cables that are too thin can create severe overheating and fire hazards. The exact cable recommendation in that manual applies to that specific example, not every system. See Deye battery manual.
Whitehouse cable and protection examples
Whitehouse stocks products such as the 50mm² black battery cable, Onesto 2P 160A Battery Disconnector, Onesto 160A Battery Fuse Link and multiple DC fuse ratings. The correct combination must be calculated around the real current and cable length.
Common cable mistakes
- Using inverter kW to choose cable without calculating DC current.
- Ignoring distance and voltage drop.
- Using undersized lugs or poor crimping.
- Using AC-only devices on DC circuits.
- Installing PV cable where it can chafe on roof edges.
- Running communication cable with high-power conductors without following manufacturer guidance.
- Increasing fuse size because a system trips instead of diagnosing the cause.
- Assuming “bigger cable is always better” without considering terminals, protection and installation practicality.
Worked current examples: why low-voltage battery cables become large
Ignoring losses for illustration, a 5kW inverter drawing from 48V requires about 104A at full output (5000 ÷ 48). An 8kW inverter is about 167A (8000 ÷ 48). Real systems can draw more because battery voltage changes and conversion is not 100% efficient. These calculations are not cable sizes—they simply show why battery wiring is a high-current circuit.
Now compare that with a PV string: several panels in series may operate at hundreds of volts while carrying only the string current. The power can be similar, but the conductor design problem is completely different.
Voltage-drop questions to ask your installer
- What maximum current is this cable designed for?
- What is the one-way cable length?
- What voltage drop was allowed?
- Is the conductor installed in free air, conduit, trunking or bundled with others?
- What protects the cable against short circuit?
- Are the lugs and terminals rated for the conductor and current?
FAQ
Is 6mm² solar cable enough for every PV array?
No. 6mm² is common in residential PV, but current, string arrangement, distance and installation conditions determine suitability.
Is 50mm² battery cable enough for an 8kW inverter?
It may or may not be. Battery voltage, maximum battery current, cable length, cable construction, installation method and manufacturer requirements must be checked.
Should positive and negative battery cables be the same length?
In many parallel battery arrangements, symmetrical/equal paths help current sharing. Follow the battery and inverter manufacturer's layout instructions.
Get a tailored Whitehouse solar or backup-power quote
Whitehouse Lighting & Electrical can help you build a solution around your actual loads, budget, property and expansion plans. We do not rely only on the products shown online; where a project needs a different inverter size, battery bank, protection arrangement or commercial configuration, we can source around the brief.
We arrange solar and backup-power solutions for homes and businesses across South Africa, including Secunda, Ermelo, Mpumalanga, Mbombela/Nelspruit, Johannesburg, the East Rand, Pretoria, North West and Bloemfontein. Panels, batteries and other bulky equipment may need a dedicated delivery quotation depending on route and handling.
Important: this guide is for planning and buying decisions. Cable sizes, protection ratings, earthing, DB alterations, PV strings and final system settings must be confirmed for the actual installation by appropriately qualified persons and the relevant manufacturer documentation.
