What Size Battery Cable Should I Use For My RV？

Upgrading your current battery system can be a little intimidating at first for everybody. What type of batteries should I use? How much power do I need? Should I try Solar Panels? Too many options tend to confuse people. Don’t worry, there are only a few key components that you need to be aware of, and the rest will fall into the right places by themselves.

One of the key components is Battery Cables for your RV. It’s essential that you use the correct wire diameter and length regardless of whether your battery is Lithium-ion or Lead-Acid. If they are too short and narrow, then that is a fire hazard waiting to happen. Too long and thick, and the voltage drop will be too great for anything to run properly.

Fortunately, this article is intended to properly guide and educate you on Battery Cables so you can make the proper buying decision for your Battery System.

What is an RV Battery Cable?

The cables coming straight from your batteries are the primary conduit of your RV’s electrical system. Since they are directly connected to the batteries, they do most of the heavy lifting. Because of this, your battery cables need to be able to handle the maximum amount of current than any other cable in your RV. To give you an idea, they handle more than 10 times the current than other cables for a much longer time as well.

What is a Wire Gauge?

The diameter or thickness of a wire is measured using a wire gauge. The AWG (American Wire Gauge Scale) is usually the standard for measuring wire gauges. The thinner the wire, the higher the cable rating in the AWG system and the less current that can flow through.

For example, 1 AWG wire is three times thicker than 10 AWG and can roughly carry four times more current than 10 AWG. It has lower resistance and is heavier and naturally cost more.

* the data from bluesea.com

What Size of Cable is Best for Your RV

Now that you have a basic understanding of what you're dealing with, it’s time to choose a cable for your RV’s electrical system. Choosing the correct length and diameter is crucial for ensuring system performance and safety.

What size cable you need for your battery wiring depends on how much electricity your RV consumes and how much distance it needs to travel. Using wires that are too thin and you can one day find your grid burning; getting too thick will cost you more, and you run into the slow torture of constant discomfort.

There are a variety of situations you can find yourself in, and as such, there isn’t really one correct answer to this problem. However, it all boils down to distance and current(amps) flowing through them.

Factors You Need to Consider When Choosing A Cable

Distance

There are two distances you need to be aware of. One is the distance between other batteries joined together, and the other to your appliances.

Figure out how far the device is from the battery. The length of the circuit is the total length of the entire circuit, which is twice the distance between the device and the battery.

More electricity can be sent over longer distances using thicker lines. To put it simply, the resistance of a cable decreases as its diameter increases. When the length of the cable increases, its resistance increases again.

Amps

The amount of current you’ll need to transfer is the major factor that decides the diameter of your wire. The more current(amps) flows through, the larger the diameter would need to be. The AWG sizing chart is really convenient and depicts varied current capabilities at different lengths.

How To Calculate How Many Amps Your RV Will Be Using?

Calculating your existing requirements is a straightforward procedure. A current and power rating will be found on the majority of your RV's appliances and equipment. If all of your devices are powered by 12 volts (the same voltage as your battery system), simply add their current ratings to determine your total current demand.

In case you are using batteries in parallel and series, simply add the voltages of the batteries that are in series. Remember, batteries in parallel do not increase the voltage of the batteries.

For example:
If you have a 4 amp lamp and it is 2 meters from the Aolithium 100ah battery, then: 4A x 1.25 (buffer factor) = 5A. 2 x 2 = 4 (meters). Then find the line 4.6 meters. The minimum wire diameter needs to be 16AWG, equivalent to 1.5 square wire.
Tip: When choosing a cable, you can add a little margin to enlarge the amperage a little (about 25% or so). There is nothing wrong with a larger-than-required wire.

Inverter

Inverters are a great way to reduce the amount of wires coming directly from your batteries. Since AC power can be delivered with thinner wires when compared to DC, you only need thicker wires long enough to reach the inverter.
If you want to use or are already using an inverter to power your appliances and equipment that run on 120 volts, then the calculations are done a bit differently.
If you are already using an inverter, then simply divide the power of your inverter, for example, 3000 watts, with the total voltage of your battery, i.e. 12 volts. The answer you will get is 250 amps. Again a 00 AWG wire is the required diameter if the inverter is close to the batteries.

If you want to buy a new inverter, just add up the total power requirements (in watts) of each gadget in your RV to figure out what size inverter you'll need. For example, if all of your appliances and devices use 2000 watts of power, you'll need a 2500-watt inverter to make sure it always keeps up.

After that, simply repeat the process like before of dividing the power (watts) of the inverter with the voltage of your battery, and you will have your amps.

Picking The Correct Battery Cable Size

When choosing your cables, merely oversizing and just buying the thickest cable isn’t the solution. Although getting bigger battery cables causes fewer problems than selecting cables that are too small; adopting too thick cables, on the other hand, may add unnecessary money, weight, and inconvenience to your project. The chart below shows the parameters on which you should buy your cables based on your needs.

Tip: When choosing a cable, it’s a good idea to leave a little room for the current capacity. There is nothing wrong with a larger-than-required wire. If 200 amps are your power usage, use a cable with a rating of 250 amps, i.e 0 AWG (can carry 245 amps) instead of 1 AWG (can carry 211 amps).

We usually refer people to wire size tables and calculators so you can get the proper wire gauge for the length and the % voltage drop you want.

Blue Sea has some good resources for the calculations for DC circuits.
Choosing the Correct Wire Size for a DC Circuit
Calculator the wire size

btw if a wire is properly protected by a fuse or breaker for its size. If the amperage value is correct for the wire there shouldn't be a risk of fire as the breaker or fuse will blow first.

You need to always properly fuse each wire run to prevent wires overheating in the case of a short circuit.

What If the Battery Cable Size Is too Small?

Voltage Drop

The first issue you may encounter is voltage loss. This indicates that the voltage at the wire's end is less than the battery's. If the voltage drops too low, your electronics may not work.
A wire's resistance is determined by its diameter (gauge). If your battery wires is too thin in diameter or too long in length, you risk having an unwanted voltage drop, which may hinder your electronics from working.

Over Heating

Overheating is another thing that occurs when the current flows through a narrow wire. In the same way that voltage loss causes more heat to be created, greater resistance causes more heat to be generated in the wire. The danger of utilizing a battery cable that is too narrow is Fire, which is significantly more harmful than high power loss. If the cables If the cable diameter is not thick enough, they might become hot enough to melt the coating and catch on fire.
RV fires usually result in the complete destruction of the RV as well as its contents. Always make sure that your wires have that extra room to accommodate extra current if needed.

What If the Battery Cable Size Is too Big?

Buying thicker wires do give you insurance when choosing wire gauges and provides less resistance and voltage drops; going too big will cost you in more ways than one.
There are 3 major disadvantages of selecting a battery cable wire gauge that is too large: cost, weight, and ease of use.

Budget

Money is most likely the major issue. Thicker wire gauges will weigh in heavy on your wallet. The additional cost will be negligible if you only need a few feet of battery cable. Cost becomes more of an issue as cable lines get longer.

Weight and Ease of Usage

The weight, like the expense, increases in lockstep with the wire gauge. Longer wires can add more weight than you might have expected.
The third drawback is that thicker wires are more difficult to deal with. Merely getting the thickest wire isn't the answer because the thicker the wire, the more expensive it is, and it may be huge, uncomfortable, and tough to work into your components.