When connecting your batteries together, it is imperative that you use the proper sized battery cables. If you use improper sized cabling, the best case scenario you can expect is that you will reduce your batteries performance and the worst case is that you could risk cable failure or even a fire resulting from the cables overheating. The best rule of thumb that I can give you is to purchase the largest or thickest cables that you can afford to reduce resistance and increase efficiency and electrical flow. Similarly, you also need to be aware of the length of the cable run. The longer the length of the cable run the greater the total resistance in the cable will be, which results in the need for thicker cables to reduce resistance. Since the length of the wire run and your specific needs will determine what size cable you need, I cannot tell you exactly what sized cable to use. I do however have some suggestions:
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Put the batteries as close to each other as possible. Preferably in the same compartment or at least in compartments right next to each other. Don’t try to mount some of the batteries in a front compartment and then the rest in a rear compartment and try to connect them together via wiring. My batteries are in the same compartment and are connected by cables no longer than 12 inches using #3/0 welding cables to reduce resistance. I am not saying that 12 inches is the limit, it is just best practice to reduce the length as much as possible. Since my batteries were mounted so closely together I could have probably gotten away with #2/0 welding cable; however, I chose the thicker #3/0 to reduce resistance and assure safe practice.
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Use as thick a cable as possible to connect your batteries. It is suggested that you use welding cable in the range of #2/0 to #4/0 gauge; however, it is really going to depend on your needs and application. Consult with your battery manufacturer or talk to an electrician about the electrical codes in your area to ensure that you are safely wiring the batteries in your RV.
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If you are connecting your batteries to an inverter like I have, make sure you follow the manufacturer’s recommendations for cable size. Similarly, try to mount the inverter as close to the batteries as possible so as to limit the length of the cable needed to connect the batteries to the inverter. Generally, I would recommend that you try to limit your cable lengths to 5 feet or less. Similarly, be careful about where you mount your inverter since it could act as an ignition source if your batteries are gassing. My inverter is mounted in a compartment right behind the batteries and the cables are run through the wall separating the two compartments and are only as long as I need to make the connection; approximately 3 feet long in length.
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Make sure that you install a catastrophic fuse or circuit breaker into the DC wiring system. It will help ensure that if you have wired anything wrong or something shorts out that you will have some protection. In my case I have a 300 Amp catastrophic fuse wired into the negative feed from my batteries. (For additional information be sure to read our articles on installing an inverter.)
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Be sure to use professionally created battery cables. There are some good sources on the web for battery cables. In my case, I was able to get custom cables made to my specification (length, size, and connector) through the same local vendor that I bought my Lifeline batteries from. If your local vendor does not make cables, they should at least be able to help you find someone who does.
Planning for the Correct Sized Battery Bank:
Planning for the correct sized battery bank is equally important as the other items that we discussed here. Failure to do so will result in a lack of power for your needs. For more information, please refer to the section “Estimating Power Consumption and Sizing Your RV Battery Bank”.
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