Lighting
LED interior lights
5 A min even for low-draw LEDs
LED light bar / flood
Nav lights (boat)
Appliances
12V compressor fridge
Startup surge ~8 A
Diesel heater
Glow plug peak at startup
Water pump
Motor: 150-200% for startup
Bilge pump
150% for motor startup
Electronics
USB outlet (dual)
12V / cigarette socket
VHF marine radio
TX draws more than RX
Chartplotter / GPS
Roof fan
High current
Inverter 300 W
Check inverter manual
Inverter 1000 W
Check inverter manual
Inverter 2000 W
Check inverter manual
DC-DC charger 30 A
Windlass / winch
Use breaker, not fuse
Solar
Solar panel 100 W
125% of Isc, DC-rated only
Solar panel 200 W
125% of Isc, DC-rated only
Main battery protection
Main fuse (small)
Within 18 cm of battery +
Main fuse (large)
Within 18 cm of battery +
Find your current draw. Read the fuse size.
Based on 125% rule at 12 V DC. Wire runs under 3 m / 10 ft.
0 - 3 A draw
0 - 36 W at 12 V
3 - 5 A draw
36 - 60 W at 12 V
5 - 8 A draw
60 - 96 W at 12 V
8 - 12 A draw
96 - 144 W at 12 V
12 - 16 A draw
144 - 192 W at 12 V
16 - 24 A draw
192 - 288 W at 12 V
24 - 32 A draw
288 - 384 W at 12 V
32 - 48 A draw
384 - 576 W at 12 V
48 - 80 A draw
576 - 960 W at 12 V
80 - 100 A draw
960 - 1200 W at 12 V
100 - 160 A draw
1.2 - 1.9 kW W at 12 V
160 - 250 A draw
1.9 - 3 kW W at 12 V
Fuse types at a glance
Blade (ATC)
1-40 A
Branch circuits, lights, electronics
Mini blade
1-30 A
Compact panels, electronics
MIDI
30-200 A
DC-DC chargers, small inverters
ANL
35-750 A
Main battery, large inverters
Class T
110-800 A
Large battery banks (20k AIC)
Glass tube
0.5-30 A
Precision electronics, instruments
Where to place fuses
- +Battery: within 18 cm / 7 in of positive terminal
- +Distribution: each branch gets its own fuse for that wire
- +Solar: between panels and controller, DC-rated only
- +Inverter: dedicated fuse on battery-side cable
- --Ground wires, wires under 18 cm, engine starter
Mistakes that cause fires
- Oversized fuse-- 100 A on 14 AWG melts the wire before the fuse blows
- No main fuse-- a short dumps the entire battery into the wire
- AC fuse on DC-- DC arcs do not cross zero; the fuse will not interrupt
- Fuse too far from battery-- unfused wire between battery and fuse is unprotected
Design your full electrical system
VoltPlan calculates fuse sizes, wire gauges, and generates a complete wiring diagram for your camper, boat, or off-grid setup.