To find the proper wire and fuse (or circuit breaker) sizes for your 3000 Watt inverter, you’ll need to calculate the maximum amp draw of the inverter.
This maximum amp draw will generally depend on 2 factors:
- The efficiency of your inverter.
- The lowest battery voltage at which your inverter draws power.
In this article, I’ll explain why these factors matter, and I’ll provide a couple of formulas that you can use to calculate the maximum amp draw of your 3000W inverter, which you can then use to determine the correct wire gauge and the correct amp rating of the fuse or circuit breaker that you need.
How many amps does a 3000 watt inverter draw?
In general, a 3000 Watt inverter can draw as much as 350 Amps if it’s running on a 12V battery bank. If the 3000W inverter is running on a 24V battery bank, it can draw up to 175 Amps of current. If the battery bank is rated at 48V, the amp draw will not exceed 90 Amps.
This is assuming the DC-to-AC conversion efficiency of the inverter (@ 3000 Watts) is around 85%. Inverters with a greater conversion efficiency (90-95%) will draw less current, and less efficient inverters (75-80%) will draw more current.
You can calculate the maximum amp draw of your 3000 Watt inverter using the following formula:
Maximum Amp Draw (Amps) = (3000 Watts ÷ Inverter’s Efficiency (%)) ÷ Lowest Battery Voltage (V)
Inverter’s efficiency:
This is the Output Power vs Input Power ratio:
Inverter’s efficiency = Output Power (Watts) ÷ Input Power (Watts)
For example, in order for a 90% efficient 3000 Watt inverter to put out maximum power (3000 Watts), it will have to draw about 3333 Watts of power from the battery:
Input Power (Watts) = Output Power (Watts) ÷ Inverter’s efficiency
Input Power (Watts) = 3000 Watts ÷ 90%
Input Power (Watts) = 3000 Watts ÷ 0.9
Input Power (Watts) = 3333 Watts
Generally, at maximum load, while high-quality Pure Sine Wave inverters are about 90 to 95% efficient, low-quality Modified Sine Wave inverters are only 75 to 80% efficient. You can refer to the documentation provided by the manufacturer to determine the efficiency of your inverter.
Lowest Battery voltage:
Power (Watts) is the product of Voltage (Volts) and Current (Amps):
Power (Watts) = Voltage (Volts) x Current (Amps)
The voltage across the terminals of the battery increases or decreases depending on its state of charge, and the current output of the battery depends on what the load requires.
For example, if our 3000 Watt inverter puts out maximum power and, for example, pulls 3300 Watts of power steadily from the battery, the battery will continue to put out 3300 Watts of power until it is disconnected.
And, while the battery is discharging, its voltage slowly decreases until it is low enough that the inverter disconnects it.
However, since Watts = Volts x Amps, in order for the battery to maintain that steady 3300 Watts of power output that the inverter requires, as the battery’s voltage decreases, its output current increases.
This means that, if our 3000 Watt inverter continuously puts out 3000 Watts of power, the amount of current that it draws from the battery will slowly increase until it reaches its Maximum right before the battery is disconnected due to low voltage.
In other words, the Maximum Amp Draw will happen when the inverter is producing its rated power (3000 Watts) at the lowest input voltage.
Now, for most inverters, the Low Voltage Disconnect (LVD), or the lowest voltage at which the inverter disconnects the battery is:
- 10 Volts if the battery bank is rated at 12V
- 20 Volts if the battery bank is rated at 24V
- 40 Volts if the battery bank is rated at 40V
However, if you have a programmable inverter or some other means to program the Low Voltage Disconnect (such as Victron’s BatteryProtect for example), the lowest input voltage, or the lowest battery voltage at which the inverter produces rated power, will depend on 3 factors:
- The voltage rating of the battery bank (12V, 24V, or 48V)
- The type of battery bank (Chemistry)
- And the allowable Depth Of Discharge (DOD) of the battery bank
To understand this, let’s first look at the following table which shows the voltage vs state of charge of different types of battery banks with different voltage ratings:
| State Of Charge (SOC) | Lead-Acid | Lithium | ||||
| 12V | 24V | 48V | 12V | 24V | 48V | |
| 100% | 13 Volts | 26 Volts | 52 Volts | 13.6 Volts | 27.2 Volts | 54.4 Volts |
| 90% | 12.75 Volts | 25.5 Volts | 51 Volts | 13.4 Volts | 26.8 Volts | 53.6 Volts |
| 80% | 12.5 Volts | 25 Volts | 50 Volts | 13.3 Volts | 26.6 Volts | 53.2 Volts |
| 70% | 12.3 Volts | 24.6 Volts | 49.2 Volts | 13.2 Volts | 26.4 Volts | 52.8 Volts |
| 60% | 12.15 Volts | 24.3 Volts | 48.6 Volts | 13.1 Volts | 26.2 Volts | 52.3 Volts |
| 50% | 12.05 Volts | 24.1 Volts | 48.2 Volts | 13 Volts | 26.1 Volts | 52.2 Volts |
| 40% | 11.95 Volts | 23.9 Volts | 47.8 Volts | 13 Volts | 26 Volts | 52 Volts |
| 30% | 11.81 Volts | 23.62 Volts | 47.24 Volts | 12.9 Volts | 25.8 Volts | 51.5 Volts |
| 20% | 11.66 Volts | 23.32 Volts | 46.64 Volts | 12.8 Volts | 25.6 Volts | 51.2 Volts |
| 10% | 11.51 Volts | 23.02 Volts | 46.04 | 12 Volts | 24 Volts | 48 Volts |
| 0% | 10.5 Volts | 21 Volts | 42 Volts | 10 Volts | 20 Volts | 40 Volts |
For example, let’s say our 3000 Watt inverter is 90% efficient and will be running on a 24V battery bank, which consists of 4 LiFePO4 (Lithium-Iron-Phosphate) batteries wired in series-parallel.
Lithium batteries can be fully discharged (100% DOD/0% SOC), which means that the voltage of our battery bank could go as low as 20 Volts.
With these pieces of information, we can calculate the Maximum Amp Draw of our inverter as such:
Maximum Amp Draw (Amps) = (3000 Watts ÷ Inverter’s Efficiency (%)) ÷ Lowest Battery Voltage (V)
Maximum Amp Draw (Amps) = (3000 Watts ÷ 90%) ÷ 20 V
Maximum Amp Draw (Amps) = (3000 Watts ÷ 0.9) ÷ 20 V
Maximum Amp Draw (Amps) = (3333 Watts) ÷ 20 V
Maximum Amp Draw (Amps) = 166.7 Amps
Now, to give another example, let’s say we’re using the same 90% efficient 3000 Watt inverter, but this time, the inverter will be running on a 24V Lead Acid battery bank.
Generally, it is not recommended to discharge Lead Acid batteries below 50% (50% DOD). If we look at the table above, we can see that at a 50% State Of Charge, the voltage of a 24V Lead Acid battery bank is 24.1 Volts.
Assuming the inverter (or LVD device) is set to disconnect the battery at 24.1 Volts, we can then calculate the maximum amp draw of our 3000W inverter as such:
Maximum Amp Draw (Amps) = (3000 Watts ÷ Inverter’s Efficiency (%)) ÷ Lowest Battery Voltage (V)
Maximum Amp Draw (Amps) = (3000 Watts ÷ 90%) ÷ 24.1 V
Maximum Amp Draw (Amps) = (3000 Watts ÷ 0.9) ÷ 24.1 V
Maximum Amp Draw (Amps) = (3333 Watts) ÷ 24.1 V
Maximum Amp Draw (Amps) = 138.3 Amps
Now that we know how to determine the maximum amp draw of our 3000 Watt inverter, we can discuss wire sizes.
What gauge wire for 3000 watt inverter?
In general, if the 3000 Watt inverter is going to run on a 24V battery bank, you should use 4/0 AWG copper wires. If the battery bank is rated at 48V, you should use 1/0 AWG copper wires with your inverter.
To properly size the wires, you can use this Inverter wire gauge calculator.
Or if you want to do the calculations yourself, simply multiply the Maximum Amp Draw of your 3000 Watt inverter by a factor of 1.25, and then use the ampacities provided in the following table to choose the correct wire gauge:
| Copper Wire Size (AWG or kcmil) | 75°C(167°F):
Types RHW, THHW, THW, THWN, XHHW, XHWN, USE, ZW |
| 14 AWG | 20 A |
| 12 AWG | 25 A |
| 10 AWG | 35 A |
| 8 AWG | 50 A |
| 6 AWG | 65 A |
| 4 AWG | 85 A |
| 3 AWG | 100 A |
| 2 AWG | 115 A |
| 1 AWG | 130 A |
| 1/0 AWG | 150 A |
| 2/0 AWG | 175 A |
| 3/0 AWG | 200 A |
| 4/0 AWG | 230 A |
| 250 | 255 A |
| 300 | 285 A |
| 350 | 310 A |
| 400 | 335 A |
For example, let’s say our 3000 Watt inverter is 90% efficient and is rated at 24VDC. Let’s also say that we’ll be running the inverter on a 24V lithium battery bank.
In the previous section, I’ve explained that with this type of battery, a 24V battery bank’s voltage can go as low as 20 Volts. And I’ve then calculated the Maximum Amp Draw of the 3000W inverter as such:
Maximum Amp Draw (Amps) = (3000 Watts ÷ Inverter’s Efficiency (%)) ÷ Lowest Battery Voltage (V)
Maximum Amp Draw (Amps) = (3000 Watts ÷ 90%) ÷ 20 V
Maximum Amp Draw (Amps) = (3000 Watts ÷ 0.9) ÷ 20 V
Maximum Amp Draw (Amps) = (3333 Watts) ÷ 20 V
Maximum Amp Draw (Amps) = 166.7 Amps
We then multiply this Max. Amp draw by a factor of 1.25:
The ampacity of the wire (Amps) should not be less than The Maximum Amp Draw (Amps) x 1.25
The ampacity of the wire (Amps) should not be less than 166.7 Amps x 1.25
The ampacity of the wire (Amps) should not be less than 208 Amps
If we look at the ampacity table above, we can see that 4/0 AWG copper wires have an ampacity of 230 Amps, which will be sufficient for this particular setup.
If the inverter is rated for 12VDC, you could use 4/0 AWG copper wires, however, you will not be able to use the full rated power of your inverter. If you use 4/0 AWG copper wires with your 12VDC-3000W inverter, your appliances should not exceed a power usage of about 2000 Watts.
As there are other factors that influence the required wire sizes, such as cable length and room temperature, I recommend using our Inverter wire size calculator to properly size your wires.
Once you determine the required wire gauge, you’ll also need to size the overcurrent protection device (fuse or circuit breaker) that you’ll need.
What size fuse (or circuit breaker) for 3000 watt inverter?
In general, if your 3000 Watt inverter is going to run on a 24V battery bank, you’ll need a 175-225 Amp fuse or circuit breaker. If the battery bank is rated at 48V, you’ll need a 90-110 Amp fuse or circuit breaker.
However, the amp rating of the fuse or circuit breaker that you use should be greater than the ampacity of the wires. If you size your wires as shown in the previous section, this should be an issue.
To size the fuse or circuit breaker correctly, multiply the maximum amp draw of your 3000 Watt inverter by a factor of 1.25 and round up to the next standard amp rating.
The standard fuse and circuit breaker amp ratings are 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000 5000, and 6000 Amps.
For example, let’s say our 3000W inverter is 90% efficient and is running on a 24V Lead Acid battery bank. Assuming we don’t discharge the battery bank below 50% SOC, the lowest battery voltage at which our inverter is going to draw power is around 24.1 Volts.
Maximum Amp Draw (Amps) = (3000 Watts ÷ Inverter’s Efficiency (%)) ÷ Lowest Battery Voltage (V)
Maximum Amp Draw (Amps) = (3000 Watts ÷ 90%) ÷ 24.1 V
Maximum Amp Draw (Amps) = (3000 Watts ÷ 0.9) ÷ 24.1 V
Maximum Amp Draw (Amps) = (3333 Watts) ÷ 24.1 V
Maximum Amp Draw (Amps) = 138.3 Amps
We then multiply this value by 1.25:
The fuse or Circuit breaker Amp rating should not be less than The Maximum Amp Draw (Amps) x 1.25
The Fuse or Circuit breaker Amp rating should not be less than 138.3 Amps x 1.25
The Fuse or Circuit breaker Amp rating should not be less than 172.9 Amps
We’ll then round up to the next standard amp rating, which is 175 Amps.
