What Size Fuse for an Inverter?
What Size Fuse for an Inverter?
The inverter manual is the starting point for its battery-side cable and fuse. Inverter output watts alone cannot settle the fuse size: efficiency, input voltage, surge time and cable installation all matter.
Estimate, then verify
Use DC input A ≈ AC output W ÷ (DC input V × efficiency). A 1000 W load at 12 V and 90% efficiency implies about 93 A; at 10.5 V and 85% it implies about 112 A. These figures help check the manual, but are not a fuse table.
Select both positive and negative cables for full-load current, routing, ambient temperature and voltage drop. The fuse on the positive lead should protect the cable close to the battery/source, tolerate legitimate operating surge according to its curve, and have appropriate DC voltage and interrupt capacity. In a battery bank, compare the protection device’s rating with the available short-circuit current and follow the battery and inverter instructions.
Never assume “4 AWG always supports 125 A” or “2/0 AWG always supports 300 A.” Ampacity changes with conductor material, insulation, termination and installation method. If the selected fuse exceeds the protected cable rating, redesign the cable and protection together.