Battery cable sizes

[Jamiebrookes]

How do I find the correct battery cable sizes etc to link my battery bank up and also where can I find information to help me find the right size buzz bar. Where's the best place to buy cables and buzz bars. Thanks

[ditchcrawler]

The BSS gives the minimum size but depending on your loads you may require larger, ie. 3KW inverter . I do not know what the RCD requirements are if its a new build

[Jen-in-Wellies]

You need three pieces of information.

1. What is the maximum current that could be drawn, or fed to the batteries with everything connected switched on?
2. What is the voltage drop you are prepared to accept, or that your equipment can cope with? Perhaps 4%? This varies with the equipment. 12V fridges are particularly susceptible.
3. How long are the cables going to be?

The voltage will drop more with higher currents, longer cables and thinner cables, so you reduce voltage drop by increasing the cable diameter. This is much more of a problem on boats than overheating cable, though that can still happen. Remember that cable length is there and back, so a battery bank 4' from a bus bar will have a cable length of 8'.

You can use an on-line calculator to work out voltage drops for different cable sizes, lengths and currents. The Boat Safety Scheme gives a minimum of 25mm² for battery cables, but if the distances are long, or you have a big inverter, then you may need to go up to 50, or 75mm². For example, on my boat, the battery to battery cables are 50mm², as is the cable to the 1600W inverter. There are cables to the bus bars for other 12V equipment like lights and pump and these are 25mm². All protected by a 250A megafuse.

For bus bar selection, work out the maximum current by adding up the load on them if everything connected were switched on. A reputable supplier will give the recommended maximum current for their bus bar.

 

12V Planet and Vehicle Wiring Products are good places to buy this stuff. The bigger marine chandlers too, ASAP, Midland SwinChandlers etc.

 

Jen

 

Edited September 4, 2019 by Jen-in-Wellies