ECN Forum Forums General Topics of the Trade General Discussion Area DC System - Grounding and fusing!

The - side is usually "grounded" because it helps reduce galvanic corrision. Water molecules are polarized- because of wave physics and molecular geometry, the electron spends relatively more times around the oxygen atom than the hydrogen atoms. As a result, the oxygen atom has a slight - charge and the hydrogen molecules a slight + charge. So, if we give the steel chassis of a car (or a building, plane, ship, flashlight, etc), it repels the oxygen atoms in water and is less likely to oxidize and corrode. The + terminal, on the other hand, agressively oxidizes, but it's a relatively small area and can be maintained with dielectric grease or cleaned off.

Vehicles and other items that aren't solidly grounded (cars, etc) will always ground - and fuse +.

On our DC circuits (UPS batteries, 384 or 480VDC), we ground the - terminals and run the + through the breakers, but I think it's more habit than anything else- it's a benign environment and considering it's grounded, grounding the + would actually make more sense from a corrosion-prevention standpoint.