Size the fuse and cable for one DC run the way the standards do it — the fuse protects the wire, and the cable is chosen to carry that fuse and stay within a safe voltage drop.
The same engine that sized this wire designs the whole system — battery, inverter, solar array, every cable and fuse — and draws the wiring diagram.
Design my system — freeNo account needed to design. Same engine, same standards as this calculator.
Two jobs, in order. The fuse protects the wire — never the device — so it is sized first, to the next standard rating at or above 125% of the continuous load. The cable is then chosen to satisfy two limits at once: it must carry the fuse on its ampacity, and it must keep voltage drop under the limit for the run length. Whichever needs more copper wins.
Region matters: the US uses AWG to ABYC E-11; Europe, the UK and Australia/NZ use mm² to ISO 13297, BS 7671 and AS/NZS 3008. Volt-drop coefficients come from IEC 60228 and already include the round trip, so you enter the one-way length.
The wire. The fuse must blow before the cable overheats, so it is sized to the conductor, then the device is protected by being on a correctly-sized circuit.
ABYC and NEC treat anything running 3+ hours as a continuous load and require the protection (and conductor) rated to at least 125% of it, leaving headroom so a normal load never nuisance-trips.
The voltage-drop coefficients already account for the current travelling out and back, so you enter the straight-line one-way distance, not the loop length.
Pick your region and the calculator switches automatically — AWG for the US (ABYC), mm² for Europe, the UK and Australia/NZ.
Wattonomy applies these standards in its calculations. It is not certified, sponsored or endorsed by ABYC, ISO, NFPA or Victron. Last reviewed June 2026 — see the methodology.
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