Skip to content
RVPowerCalc

Wiring

What Size Wire for 150 Amps at 5 Feet? (12V RV)

Researched from published standards and manufacturer specifications. Updated .

Quick answer

Carrying 150 amps over a 5 foot one-way run on a 12 volt system needs 2 AWG copper to stay inside the 3 percent voltage drop limit ABYC sets for critical circuits. That conductor drops about 0.291V, or 2.42 percent. Protect it with a 200 amp fuse.

Wire sizing has two separate tests and a conductor has to pass both. The first is ampacity: can the wire carry the current without overheating? The second is voltage drop: does enough voltage actually arrive at the other end? On 12 volt systems voltage drop almost always decides, because there is so little voltage to lose in the first place.

The formula doubles the run length, and that doubling is the most commonly missed step in RV wiring. Current flows out on the positive conductor and back on the negative, and it drops voltage in both. Check your own combination on the wire gauge calculator.

What gauge wire for 150 amps at 5 feet?

ABYC E-11 sets two voltage drop limits: 3 percent for critical circuits such as panel feeds and electronics, and 10 percent for non-critical circuits such as lighting. Both answers are below.

Conductor size for 150 amps over a 5 foot one-way run at 12V
Voltage drop limitApplies toSmallest conductorActual drop
3 percentCritical circuits, panel feeds, electronics2 AWG0.291 V (2.42%)
10 percentNon-critical circuits, lighting, accessories4 AWG0.462 V (3.85%)

Published standard Source: ABYC E-11 voltage drop limits and ampacity, with NEC Chapter 9 Table 8 conductor resistance.

How does the answer change with run length?

Voltage drop is directly proportional to length, so doubling the run doubles the drop and pushes you up the gauge table. This is the same 150 amps at a range of distances.

Conductor size for 150 amps at 12V by run length, 3 percent drop limit
One-way runSmallest conductorVoltage dropVoltage arriving
3 ft4 AWG0.277 V11.72 V
5 ft2 AWG0.291 V11.71 V
10 ft2/0 AWG0.29 V11.71 V
15 ft3/0 AWG0.345 V11.66 V
20 ftNone up to 4/0--
25 ftNone up to 4/0--
30 ftNone up to 4/0--

Published standard Source: NEC Chapter 9 Table 8 resistance, ABYC E-11 ampacity.

Would 24 volts solve this?

Yes, and dramatically. At 24 volts the same power moves at half the current, and voltage drop as a percentage falls by a factor of four. The same load at 24 volts needs only 8 AWG over 5 feet. This is the whole argument for higher system voltage in a large build, and it is why big inverters are increasingly sold in 24 and 48 volt versions.

What fuse goes with 150 amps?

A continuous 150 amp load is protected at 125 percent, which is 187.5 amps, rounded up to the next standard rating of 200 amps. The conductor must be rated to carry at least as much as the fuse, because the fuse exists to protect the wire. Fitting a fuse larger than the wire can carry defeats the entire point of having one. See the fuse size calculator.

Cable, lugs and overcurrent protection

Frequently asked questions

What gauge wire do I need for 150 amps at 5 feet?
2 AWG copper, if you are holding to the 3 percent voltage drop limit ABYC applies to critical circuits. That conductor loses about 0.291 volts over the round trip. On a non-critical circuit such as lighting, where 10 percent is acceptable, 4 AWG would do.
Why does the run length get doubled in the voltage drop formula?
Because current has to return. It flows out along the positive conductor to the load and back along the negative conductor to the battery, and it drops voltage in both directions. A 10 foot one-way run is 20 feet of conductor as far as voltage drop is concerned. Forgetting this halves the calculated drop and undersizes the cable by a full step or more.
Is ampacity or voltage drop the limiting factor at 12 volts?
Voltage drop, nearly always. A 12 volt system has so little voltage to spare that a 3 percent limit is only about 0.36 volts, and a conductor big enough to stay under that is usually well above what ampacity alone requires. On higher voltage systems the balance shifts and ampacity starts to govern more often.
Can I use welding cable or automotive wire instead?
Welding cable is fine electrically and is finely stranded, which makes it flexible and easy to route, but check that the insulation is rated for the temperature and oil exposure where it runs. Cheap automotive wire is sometimes copper clad aluminum rather than pure copper, which has higher resistance than the gauge suggests and will not meet these figures. Confirm pure copper before buying.

Wiring safety. Never exceed a conductor's rated ampacity, and always fuse a circuit at or below what the wire can carry, because the fuse protects the wire rather than the appliance. Fuse every positive conductor as close to the battery as practical. Use proper crimped lugs and heat shrink rather than twisted joints, support cable so it cannot chafe through on a frame edge, and keep the battery compartment ventilated. Permanent AC wiring is work for a qualified RV technician or a licensed electrician.