How important is the lenght of the system cable from the batteries to the fuse/switch/etc?

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Neo Nos asked Jan 22, '24

How important is the lenght of the system cable from the batteries to the fuse/switch/etc?

The Victron Lithium Battery indicates:

Take care that the cross-sectional area of the system cable is equal to the cross-sectional area of the string cable, times the number of strings.

How important is this? My wire is just as long as my parallel connection wires. However I went from 4AWG to 2AWG on that wire since there is more current. I currently only have 2 x 200AH batteries but plan to add 2 more.

I had never came across such a concept and most videos I see online don't mention anything. Just want to make sure I take the best care of my Victron equipment. Any notes would be appreciated.

Reference: https://www.victronenergy.com/media/pg/Lithium_Battery_Smart/en/installation.html#UUID-6fcc6199-0f8e-33d5-5afe-7d051ebc415c

Lithium Battery 2 wire bms

2 |3000

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Answer 1 · 2024-01-22T06:25:09Z

kevgermany answered · Jan 22 at 06:25 AM

You don't say how your batteries are connected. But the statement is critical.

For example if you have 4 batteries connected in 2 parallel strings and the maximum total load on the system is 200A. Each string will only see a maximum load of 100A. So the string cabling is sized for the 100A load, but once the strings join, cabling is sized for 200A.

Cable sizes are increased as distance from battery to loads increases. This reduces voltage drop under load.

Fuses should be as close to the battery as practical. A fault in the insulation of the unfused length of cable will allow full battery power to flow. This can cause fires. Similarly chargers should have their output side fused for max charge current.

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Answer 2 · 2024-01-22T08:15:02Z

klim8skeptic answered · Jan 22 at 08:15 AM

@Neo Nos It would be good to look at the cable data from this site.

0 AWG cable can handle 120a.

2 AWG cable can handle 92a.

4 AWG cable can handle 68a.

What batteries? What is the largest load expected? Charging current expected?

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