FAQ: Why is a negative (minus) 48V DC used on some battery powered systems?

Answer: This FAQ is answered on many web pages. So we reply just in short: The main reason is that  in the original old types of plain analog systems the DC power was transferred in long cables and metallic wires. In order to reduce the galvanic corrosions the positive grounding was used. This means the positive pole is connected to ground and all switching (e.g. fuses, contactors, and relays) are connected on the minus pole wirings. This type of installation is more advantageous for so called cathodic protection.

The anti-galvanic measures are still needed to be applied for long wires, for installations with wet areas and for marine systems.

However for small size home installations with galvanic separation (e.g. by high-frequency inverters) there is no need to observe the negative polarity for the DC systems. In home or small size indoor installations there are very short DC cables with no risks of galvanic corrosions.  Such systems usually use either a negative grounding (battery minus grounded) or no grounding (floating DC potential).