DC Wire Gauge Chart: Amp Ratings for 12V, 24V, 48V

A DC wire gauge chart needs two numbers for each copper size: ampacity, the current the wire can carry without overheating (NEC Table 310.16), and resistance, which sets your voltage drop (NEC Chapter 9 Table 8). The quick answer: for 30 amps DC at 3% voltage drop, a 10ft run needs 6 AWG at 12V, 8 AWG at 24V and 10 AWG at 48V. In low-voltage systems, voltage drop usually decides the size before ampacity does, so the charts below give you both.

The video above comes from an electrical instructor and walks through the two standard voltage drop formulas from the code book: checking the drop on a wire you already have, and sizing a wire from the 3% “permitted” drop. Its examples are 120V and 240V circuits, and the same math works for 12V, 24V and 48V DC, which is exactly what this guide applies it to.

Electrical work can be dangerous: follow the manual, fuse and size every cable correctly, and use a licensed electrician for anything connected to household wiring.

DC Wire Amp Rating Chart (AWG)

This is the copper ampacity table from NEC Table 310.16, with the three insulation temperature columns, plus the resistance of each size from Chapter 9 Table 8. Ampacity is the same whether the current is AC or DC; what changes in low-voltage DC is how quickly voltage drop becomes the limit.

AWG (copper)	60°C	75°C	90°C	Ω per 1,000ft (stranded)
18	—	—	14A	8.08
16	—	—	18A	5.08
14	15A	20A	25A	3.14
12	20A	25A	30A	1.98
10	30A	35A	40A	1.24
8	40A	50A	55A	0.778
6	55A	65A	75A	0.491
4	70A	85A	95A	0.308
3	85A	100A	115A	0.245
2	95A	115A	130A	0.194
1	110A	130A	145A	0.154
1/0	125A	150A	170A	0.122
2/0	145A	175A	195A	0.0967
3/0	165A	200A	225A	0.0766
4/0	195A	230A	260A	0.0608

Ampacity: NFPA 70 (NEC) 2023, Table 310.16, copper, not more than three current-carrying conductors, 30°C ambient. 18 and 16 AWG are only listed in the 90°C column (14A and 18A). NEC 240.4(D) limits overcurrent protection on 14, 12 and 10 AWG to 15A, 20A and 30A in most building wiring. Higher temperatures, bundling and conduit fill reduce ampacity, and terminal ratings (often 75°C) limit the column you can use. Resistance: NEC Chapter 9, Table 8, uncoated stranded copper at 75°C.

In practice, most people use the 75°C column, because that is the rating of most lugs, breakers and busbars. The 90°C column is useful for derating calculations when your cable is rated 90°C or 105°C, as most good battery cable is.

What Size Wire for 30 Amps DC?

Thirty amps is a common DC load: a 30A MPPT solar charge controller, a 30A DC-DC charger, or a small inverter running a few hundred watts at 12V. The table below gives the smallest copper gauge that both carries 30A (75°C column) and keeps voltage drop at or under 3%.

System	10ft one-way	20ft one-way	30ft one-way
12V (0.36V allowed)	6 AWG (2.5%)	3 AWG (2.4%)	2 AWG (2.9%)
24V (0.72V allowed)	8 AWG (1.9%)	6 AWG (2.5%)	4 AWG (2.3%)
48V (1.44V allowed)	10 AWG (1.6%)	8 AWG (1.9%)	8 AWG (2.9%)

Distances are one-way. A DC circuit has a positive and a negative conductor, so the current travels the full round trip: a 10ft run is 20ft of wire. Percentages are the actual calculated drop with the listed size.

How the 30A answers are calculated

Voltage drop = 2 × one-way length (ft) × amps × resistance (Ω per 1,000ft) ÷ 1,000. The 2 is the round trip. Your allowed drop at 3% is 0.36V on 12V, 0.72V on 24V and 1.44V on 48V.

1. 12V, 10ft, 30A on 10 AWG: 2 × 10 × 30 × 1.24 ÷ 1,000 = 0.74V, about 6.2%. Too much.
2. Step up to 8 AWG: 2 × 10 × 30 × 0.778 ÷ 1,000 = 0.47V, about 3.9%. Still over.
3. Step up to 6 AWG: 2 × 10 × 30 × 0.491 ÷ 1,000 = 0.29V, about 2.5%. Within 3%, so 6 AWG it is.
4. The same 30A at 48V over 10ft on 10 AWG drops the same 0.74V, but that is only 1.6% of 48V, so 10 AWG works.

The video does the same thing with circular mils: circular mils = 2 × K × amps × length ÷ allowed drop, where K is 12.9 for copper, and then you pick the wire from the area column of Chapter 9 Table 8. For 30A at 12V over 10ft that is 2 × 12.9 × 30 × 10 ÷ 0.36 = 21,500 circular mils, which lands on 6 AWG (26,240 cmil), the same answer as the resistance method.

The big takeaway is how much a higher system voltage helps. The same 30A that needs 2 AWG at 12V over 30ft only needs 8 AWG at 48V. That is why so many larger systems move up in voltage; see 12V vs 24V vs 48V for the full comparison.

What Size Wire for 20 Amps DC?

Twenty amps covers things like a 12V fridge, a small DC-DC charger, or a 20A solar charge controller. Ampacity alone allows 12 AWG (25A at 75°C), but voltage drop quickly calls for bigger wire at 12V.

System	10ft one-way	20ft one-way	30ft one-way
12V (0.36V allowed)	8 AWG (2.6%)	4 AWG (2.1%)	3 AWG (2.4%)
24V (0.72V allowed)	10 AWG (2.1%)	8 AWG (2.6%)	6 AWG (2.5%)
48V (1.44V allowed)	14 AWG (2.6%)	10 AWG (2.1%)	8 AWG (1.9%)

At 48V over 10ft the voltage drop math allows 14 AWG, but 14 AWG is limited to a 15A fuse under NEC 240.4(D) in building wiring, so 12 AWG is the practical choice for a 20A fuse.

What Size Wire for 40 Amps DC?

Forty amps is typical of a 40A MPPT charge controller output or a mid-size DC-DC charger.

System	10ft one-way	20ft one-way	30ft one-way
12V (0.36V allowed)	4 AWG (2.1%)	2 AWG (2.6%)	1/0 AWG (2.4%)
24V (0.72V allowed)	8 AWG (2.6%)	4 AWG (2.1%)	3 AWG (2.4%)
48V (1.44V allowed)	8 AWG (1.3%)	8 AWG (2.6%)	6 AWG (2.5%)

What Size Wire for 50 Amps DC?

Fifty amps shows up on 50A DC-DC chargers like the Victron Orion XS and on larger charge controllers.

System	10ft one-way	20ft one-way	30ft one-way
12V (0.36V allowed)	4 AWG (2.6%)	1 AWG (2.6%)	2/0 AWG (2.4%)
24V (0.72V allowed)	6 AWG (2.0%)	4 AWG (2.6%)	2 AWG (2.4%)
48V (1.44V allowed)	8 AWG (1.6%)	6 AWG (2.0%)	4 AWG (1.9%)

For a Victron Orion XS, the guide to getting full amps from the Orion XS shows why short, thick cables matter for DC-DC chargers.

What Size Wire for 100 Amps DC?

A hundred amps is inverter territory: roughly a 1,000W inverter at 12V or a 2,000W inverter at 24V.

System	10ft one-way	20ft one-way	30ft one-way
12V (0.36V allowed)	1 AWG (2.6%)	3/0 AWG (2.6%)	beyond 4/0 (4/0 = 3.04%)
24V (0.72V allowed)	3 AWG (2.0%)	1 AWG (2.6%)	2/0 AWG (2.4%)
48V (1.44V allowed)	3 AWG (1.0%)	3 AWG (2.0%)	2 AWG (2.4%)

At 12V over 30ft even 4/0 is just over 3%, so shorten the run, run parallel conductors, accept a little more drop on a short-duty load, or move to 24V. Ampacity alone allows 3 AWG (100A at 75°C), but the inverter manual usually specifies larger cable, and its minimum always wins.

How to Pick the Right Wire Size

1. Work out the amps. Amps = watts ÷ volts. For an inverter, use its maximum DC input current from the datasheet, or watts ÷ efficiency ÷ battery voltage. For continuous loads, multiply by 1.25.
2. Check ampacity. Pick the smallest gauge in the amp rating chart whose ampacity covers that current, usually in the 75°C column.
3. Check voltage drop. Measure the one-way run, double it for the round trip, and run the math, or use the voltage drop calculation guide. If the drop is over 3%, step up a size until it fits. Use the larger of the two sizes.
4. Size the fuse to the wire. Fuse the positive conductor as close to the battery as practical, at or below the wire’s ampacity, so the fuse protects the wire. See what size fuse do I need.
5. Terminate it properly. Use lugs rated for the cable and a proper crimper; see how to crimp battery cable.

Worked Example: Sizing a 24V Inverter Cable

Illustrative inputs: a 2,000W inverter on a 24V battery, 8ft one-way (16ft round trip), target drop of 3% or less.

Step	Math	Result
DC current (assume 90% efficiency)	2,000 ÷ 0.9 ÷ 24	about 93A
Allowed drop at 3%	24 × 0.03	0.72V
Max resistance	0.72 ÷ 93	0.0077Ω
Per 1,000ft (16ft run)	0.0077 ÷ 16 × 1,000	0.48Ω per 1,000ft
Smallest size at or below that	NEC Ch. 9 Table 8	6 AWG (0.491Ω) is just over; 4 AWG (0.308Ω) fits

Now check ampacity: 4 AWG copper with 90°C insulation is rated 95A in NEC Table 310.16, and 93A × 1.25 for continuous use is about 116A, so many installers step up to 2 AWG for margin. Always follow the inverter manual’s minimum cable size. The same inverter on 12V would draw about 185A, which is why 12V vs 24V vs 48V matters.

Same Load, Three Voltages

2,000W inverter	DC amps	Typical cable for 8ft, 3% drop
12V	about 185A	2/0 to 4/0 AWG
24V	about 93A	4 to 2 AWG
48V	about 46A	8 to 6 AWG

Calculated from Table 8 resistances; confirm with your equipment manual.

Wire Types and Standards

Battery cable and welding cable use many fine strands for flexibility, and both are widely used in mobile systems. Some lugs and terminals are only listed for standard Class B stranding, so match lugs and crimpers to the cable class. Welding cable may not be listed for building wiring, so check the code that applies to you. Look for cable with a 90°C or 105°C insulation rating, and use the ampacity column that matches your terminals.

These charts are for copper. Aluminum needs larger sizes and terminals rated for it; in the video’s formula its K constant is 21.2 instead of 12.9 for copper. Boats follow ABYC E-11 tables, and vehicles often use SAE wire; both differ from NEC building wire, so use the standard that applies to your installation and the equipment maker’s manual.

Putting It to Work

If you are planning a full build, the Victron off-grid system wiring diagram and the Victron camper van electrical build show where each of these cable sizes goes in a real system. For a portable power station, the EcoFlow Delta 3 Max solar setup guide covers panel wiring and extension cable runs, where the same voltage drop logic helps you get the most from your panels.

Sources: NFPA 70 (NEC) 2023: Table 310.16 (ampacity), Chapter 9 Table 8 (conductor resistance and area), 240.4(D) (small conductor overcurrent protection); ABYC E-11 (marine). Voltage drop figures calculated from Table 8 resistances. Accessed Oct 2026.

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