RV 12 V Electrical Panel Wiring: Fuse and Wire Size by Circuit, Battery Disconnects, Busbars, ANL and Class T Fuses, and the ABYC E-11 Rules That Apply on the Road
Sep 10, 2026
Summary: A 12 V DC system is built from the battery outward: a main fuse within 7 in of the battery positive (ABYC E-11.10, adopted by RVIA for lithium banks), a battery disconnect switch, a positive busbar feeding a fused distribution panel, and a negative busbar bonded to the chassis at one point. Main fuse type follows battery chemistry: Class T for lithium (LiFePO4) banks because their short-circuit current exceeds 10 kA; ANL or MRBF for lead-acid and AGM at 2 to 5 kA; MRBF for a single battery terminal. Size every conductor for the fuse that protects it, then upsize for 3 percent voltage drop at the circuit length: at 12 V, 10 A over 15 ft round trip needs 12 AWG, 30 A over 20 ft needs 6 AWG, 100 A over 6 ft needs 2 AWG, 200 A inverter feeds over 6 ft need 2/0. Use tinned copper stranded wire (UL 1426 boat cable or SAE J1128 GXL/TXL), ring terminals crimped with heat shrink, and fuse every positive conductor at its source.
System layout
- Battery bank with interconnects sized for the inverter or charger peak, equal-length parallel cables, tinned lugs.
- Main fuse on the positive within 7 in of the terminal (ABYC E-11.10.1.1.2 allows 72 in if the conductor is in a sheath or enclosure, but 7 in is the rule of thumb inspectors apply to lithium).
- Battery disconnect switch rated for the bank's continuous current (typically 275 to 600 A), accessible without tools.
- Positive busbar after the disconnect, insulated base, covered.
- Branch fuse panel (blade fuse block) fed from the busbar through a fused feeder; loads leave here.
- High-current loads (inverter, DC-DC charger, solar controller output) each fed directly from the positive busbar through their own fuse or breaker, not through the blade panel.
- Negative busbar collecting every return; one bond to the chassis or the engine block with a cable at least as large as the largest positive; battery monitor shunt in the negative before the busbar.
Main fuse by battery type
| Battery | Prospective short-circuit current | Fuse type | Interrupt rating | Typical size |
|---|---|---|---|---|
| LiFePO4 100 to 400 Ah | 10 to 20 kA or more | Class T (JLLN) | 20 kA at 125 V DC | 150 to 400 A per bank feed |
| AGM or flooded, 2 to 4 group 31 | 2 to 5 kA | ANL, or MRBF on the terminal | ANL 6 kA at 32 V; MRBF 10 kA at 14 V | 100 to 300 A |
| Single 12 V battery, small system | 1 to 3 kA | MRBF terminal fuse | 10 kA | 40 to 150 A |
| Any, 24 or 48 V lithium | Higher | Class T | 20 kA at 125 V DC | Per inverter |
Interrupt rating matters more than amperage: a fuse that cannot break the fault current arcs and stays conductive. ANL fuses are rated 6 kA and are not adequate on a lithium bank.
Wire size: ampacity and voltage drop
Two checks, take the larger. Ampacity per ABYC Table 6A for 105 C wire outside engine spaces: 14 AWG 35 A, 12 AWG 45 A, 10 AWG 60 A, 8 AWG 80 A, 6 AWG 120 A, 4 AWG 160 A, 2 AWG 210 A, 1/0 285 A, 2/0 330 A, 4/0 445 A (derate 15 percent in an engine compartment). Voltage drop at 12 V, 3 percent (0.36 V), round-trip length:
| Load | 10 ft round trip | 15 ft | 20 ft | 30 ft | 40 ft |
|---|---|---|---|---|---|
| 5 A (lights, fans) | 16 AWG | 14 | 14 | 12 | 10 |
| 10 A (pump, TV, Starlink) | 14 AWG | 12 | 12 | 10 | 8 |
| 15 A (12 V fridge, USB-C 100 W) | 12 AWG | 10 | 10 | 8 | 6 |
| 30 A (DC-DC charger, awning, jacks) | 10 AWG | 8 | 6 | 6 | 4 |
| 50 A (solar controller output, 600 W) | 8 AWG | 6 | 4 | 4 | 2 |
| 100 A (1000 W inverter, windlass) | 4 AWG | 2 | 2 | 1/0 | 2/0 |
| 200 A (2000 W inverter) | 2/0 | 2/0 | 4/0 | 4/0 | Relocate the inverter |
Round trip means positive run plus negative return. Inverters sit within 6 ft of the bank for this reason. Use 10 percent drop only for non-critical loads like lighting on a long run; use 3 percent for anything with electronics.
Branch fuse sizes
| Circuit | Wire | Fuse (blade or breaker) |
|---|---|---|
| LED lighting run | 14 AWG | 10 A |
| Water pump | 12 AWG | 15 A |
| 12 V compressor fridge | 10 AWG | 15 to 20 A |
| Furnace blower | 12 AWG | 15 A |
| Starlink Mini via car charger or DC socket | 12 AWG | 10 to 15 A |
| USB-C 100 W outlet | 10 AWG | 15 A |
| Roof fan | 14 AWG | 10 A |
| Slide or awning motor | 8 to 6 AWG | 30 to 40 A breaker |
| DC-DC charger 30 A, both ends | 6 AWG | 40 A |
| Solar controller output 40 A | 6 AWG | 50 A |
| 1000 W inverter | 2 AWG | 150 A Class T or ANL |
| 2000 W inverter | 2/0 | 250 A Class T |
| 3000 W inverter | 4/0 | 400 A Class T |
The fuse protects the wire, not the device; size the fuse to the conductor ampacity and let the device's own protection handle the device.
Terminations and hardware
- Tinned copper ring terminals, crimped with a ratcheting crimper to the lug marking, adhesive-lined heat shrink over every crimp; no wire nuts, no bare spade terminals on power.
- Battery lugs: tinned copper, long barrel for fine-strand cable, per the die chart; no more than four terminals on one stud (ABYC E-11.14.4.7).
- Busbars rated above the main fuse, covered, with terminals torqued and marked.
- Negative bond to chassis: one point, cable equal to the largest positive, a clean paint-free surface, star washer, protected with dielectric grease.
- Every circuit labeled at the fuse panel and both ends of long runs.
- Loom or conduit through bulkheads with grommets; secure every 18 in (ABYC E-11.15.1).
- Lithium banks: BMS low-temperature charge cutoff, and a battery disconnect that isolates the inverter precharge.
Quick answers
What fuse goes on a lithium battery? A Class T fuse rated for the bank's feed current, within 7 in of the positive terminal, because LiFePO4 short-circuit current exceeds the 6 kA rating of ANL fuses.
What gauge wire for a 2000 W inverter? 2/0 tinned copper for runs to 15 ft round trip with a 250 A Class T fuse; mount the inverter within 6 ft of the bank.
How close does the fuse need to be to the battery? Within 7 in of the positive terminal per ABYC E-11.10, or within 72 in if the conductor is in a protective sheath the whole way.
What wire for a Starlink Mini in an RV? 12 AWG on a 10 to 15 A fuse for runs to 20 ft round trip; 10 AWG beyond.
Conversions Tech stocks tinned battery lugs, busbars and fuse blocks, RV and marine cable, 12 V outlets and USB-C, and Starlink 12 V power. Install guide: Starlink Mini on 12 V. OEM and dealer kits on the RV and marine OEM page.
