Cross-section follows the current and the run length, not the inverter’s badge. At 12 V, a given wattage draws roughly ten times the current it would at mains voltage, so the cable that feeds it is far thicker than people expect.
Low voltage is what makes this shelf unforgiving: the same power needs roughly ten times more current at 12 V than at mains voltage, and current is what heats a cable.
The three inputs
Sizing needs the current the load draws, the total length of the run — there and back, not one way — and the voltage drop you are willing to accept. Those three produce a cross-section, and the maker of the inverter publishes the first of them as a maximum input current.
Why cross-section and gauge are not the same table
European cable is sold in square millimetres, North American cable in AWG numbers that run backwards, and the two do not line up exactly. A conversion table is a conversion, not an equivalence, and a supplier that prints both is stating the one it actually manufactures to.
What else is in the circuit
A fuse close to the battery, rated for direct current, and sized to protect the CABLE rather than the appliance. Terminals crimped rather than twisted. A connector pair rated for the current. Each of those is a place where resistance appears, and resistance at a joint produces heat at the joint.
The part that has the last word
Every inverter manual specifies a maximum cable length and a minimum cross-section for its input. That instruction is written for that unit, and it takes precedence over any general table — including this page.
What people ask before they order
Why does length matter as much as current?
Because voltage drop accumulates along the run. A cable that is comfortable at half a metre can lose enough over four metres to make an inverter shut down on low voltage while the battery is still half full.
Are the cables in the box always sufficient?
They are sized for the length supplied. Extending them, or replacing them with something longer, changes the calculation entirely and the maker’s figure no longer applies.
Last reviewed 16 September 2026