Cable Size and Fuse Rating

If you know the ampacity of the wire used at the terminals of your battery, the fuse you use should have an amp rating equal to or lower than the ampacity of the wire. 

The size of the fuse that you need for your 100Ah battery must be 25% higher than the Amps you’re planning on drawing at battery voltage (48 Volts for example), and lower than or equal to the ampacity of the wire you’re using for your battery.

Generally, a 48V-100Ah battery is designed to output up to 100 amps at 12 volts, if your appliances do not require more than 100 amps (@12Volts), and you’re using a 1/0 AWG pure copper wire, a good fuse size for this amount of current and wire size would be 110A or 125A.

However, you might not need that big of a wire or fuse if your appliances require less than 100 Amps at battery voltage.

To properly size your fuse, you’ll first need to determine the maximum amount of current that you want to be able to draw at battery voltage. You can do that by using one of the following formulas.

If you’re using an inverter:

Maximum Amp Draw = (Continuous Power Rating of the inverter (Watts) ÷ Lowest Battery Voltage (Volts)) ÷ 0.85

Here's another example on how to calculate the cable size and fuse rating:

1. Calculate the total current draw of the load. This can be done by multiplying the power rating of the load by the voltage. For example, if you have a light bulb with a power rating of 50 watts and a voltage of 12 volts, the total current draw would be 50 / 12 = 4.17 amps.
2. Find the appropriate cable size. You can use a cable size calculator or a table of cable sizes to find the appropriate cable size for the current draw. The cable size is typically measured in American Wire Gauge (AWG) or millimeters squared (mm²).
3. Calculate the fuse rating. The fuse rating should be slightly higher than the total current draw of the load. This will allow for a margin of error and prevent the fuse from blowing if the load draws more current than expected. The fuse rating is typically measured in amps.

Here is an example of how to calculate the cable size and fuse rating:

• Load current draw: 4.17 amps
• Cable size: 14 AWG
• Fuse rating: 5 amps

It is important to note that these are just general guidelines. The specific cable size and fuse rating that you need will depend on the specific application. It is always best to consult with an electrician if you are unsure of what size cable or fuse to use.

Here are some additional factors to consider when calculating cable size and fuse rating:

• The length of the cable run.
• The ambient temperature.
• The type of cable insulation.
• The voltage drop requirements.

Here are some additional things to keep in mind when calculating cable size and fuse rating:

• You should always size the cable to be larger than the fuse rating. This will help to protect the cable from overheating in the event of a short circuit.
• You should also consider the length of the cable when calculating the cable size. The longer the cable, the larger the cable size will need to be.
• You can find cable size and fuse rating charts online or in electrical code books.

Always consult your manuals, read your warranty guides and seek advice from professionals (electricians or wireman).