How do you size cables between battery and inverter?

Start with the actual current and one-way length. At 48 V, current is high: use short copper cables with an appropriate minimum cross-section, often 35 or 50 mm². The CEG tool gives a minimum cross-section, not a signed electrical design.

What cable size is needed for PV?

Between panels and inverter, use tinned copper solar cable (H1Z2Z2-K). Cross-section depends on current and length. 4 mm² is a minimum reference; longer runs may require 6 or 10 mm².

Copper or aluminium cables?

IACS 100 copper conducts better. Electrical-grade aluminium is about IACS 61 and needs roughly 1.6 times the cross-section. CEG kits use copper. Tinned copper is protected copper with the same cross-section.

Free CEG tool

CEG copper cable size calculator

Friends of the channel: one tool for copper cables. Choose the connection (battery to inverter, panels, 230 V household or three-phase), then enter current and length. It estimates the minimum cross-section and the voltage drop . The tool already accounts for the target drop: about 1% for batteries, 1.5% for panels and 3% for household circuits. No separate calculation is needed.

Copper cable sizing

Friends of the channel: copper is the material I use in CEG kits. The international IACS scale rates annealed copper at 100. Electrical-grade aluminium (type 1350) is around 61: about 61% of copper’s conductivity, about 39% lower, not 60%. For the same current, roughly 1.6 times the cross-section is needed. This tool covers good-quality copper cables only.

The physics is the same worldwide: more current and greater length require a larger cross-section. At 48 V, current is high, so battery-to-inverter cables should be short and thick. At 230 V, the same power can use a smaller cable. Voltage-drop targets: about 1% for batteries, 1.5% for panels and 3% for household circuits.

Bare and tinned copper: tin is a thin coating on copper, not the conductor. The copper cross-section stays the same. Tinning protects strands against oxidation in damp, coastal and rooftop conditions. H1Z2Z2-K solar cables use tinned copper: the same calculated cross-section, with better long-term protection. Tinning does not require a larger cable.

Aluminium: this does not mean ‘1.6% more’. It needs about 1.6 times the copper cross-section (e.g. 25 mm² copper → about 35–50 mm² aluminium). This tool does not size aluminium cables.

Enter numbers without thousands separators, for example 3000. Results use English formatting: 3,000 W and 3.5 kW.

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Calculate cable cross-section

Current, length and minimum copper cross-section.

Which connection

Battery–inverter: high current, short and thick cable. Panels: lower current. Household 230 V or three-phase: household loads.

Current (amps)

Current flowing through this cable. Example: 100 A between battery and inverter, 30 A in a household circuit. These are not kWh.

One-way length (metres)

One direction only, for example 4 m. The tool also accounts for the return path.

Cable installation method

In conduit, the cable gets hotter and may need a larger cross-section. In free air, it dissipates heat better.

Voltage (volts)

48 or 51.2 V for the battery, 230 V for household circuits, 400 V for three-phase. It adjusts automatically when you change the connection.

Voltage adjusts automatically when you change the connection. Length is measured one way: the tool also accounts for the return path. The result is the minimum cross-section in copper: a larger size may be used, not a smaller one.

PV cables: copper, tinned copper and aluminium

For curious readers. Not needed to use the tool, but helpful when choosing the right cable.

The conductor I use in CEG kits is copper. The IACS scale rates annealed copper at 100. Electrical-grade aluminium (alloy 1350) is around 61: 61% of copper’s conductivity. This is about 39% lower, not ‘60% lower’. For the same current it needs about 1.6 times the cross-section. Example: 25 mm² copper → 35–50 mm² aluminium. Aluminium is lighter and cheaper; for household circuits and 48 V storage, I prefer copper.

The term tinned copper means copper strands with a thin tin coating. Copper carries the current and the cross-section remains unchanged. Tinning protects bare copper from outdoor oxidation and deteriorating contacts. H1Z2Z2-K / FG21M21 panel cables use class 5 tinned copper for rooftop, damp and salt-air environments. Between battery and inverter, I use correctly sized copper cables kept as short as possible.

The tool gives the minimum copper cross-section. You can increase the cross-section, not reduce it. Installation, conduit, temperature and fuses remain the electrician’s responsibility. For CEG custom cables: materials.

Other tools

PV and battery sizing · Battery autonomy · Panels in series · CEG custom cables