24v & 48v ground hookup

solarhills99

Dumb question for someone who has been at this for 40 yrs. but I have both a 24v and a 48v battery bank.  I have to hook up the grounding wires to the same buss going out to my rod, yes?

BB.

Safety Grounding....

Assuming that both systems are in the same home/cabin/power shed, and share "metallic" items (electrical boxes, conduit, even on the AC inverter output side), then yes, connecting the Negative 24 VDC battery bus to the same ground rod/cold water pipes, AC grounding, etc. allows any short circuit from 24+, 48+, 120/240VAC, etc. to exposed metal (conduit, sinks, plumbing, electrical cabinets, etc.) to find a path the the common ground connection (typically at "the ground rod" can then find a return path to the "source (batteries, AC inverter output, etc.) and trip those fuses/breakers/electronic shut downs (prevent fire, electrocution potential, etc.).

For "safety grounding", a single point of ground for all of the AC and DC systems helps ensure there is only one path through the safety grounding system.

What we don't want is "multi-point" grounding (in general) because if we do two or more connections between "return" (DC negative, AC neutral wiring, etc.) then the green wire and (white/negative) wiring is in parallel, and the normal current flow is now "shared" between the power cables (hot/return/etc.) and green wire safety ground--Which we don't want.

There can be a case made for multi-point grounding to ground rods... Typically for lightning protection (i.e., a solar array mount tied to local earth ground rod, then 6 AWG cable from remote ground rod to local power shed/home "master" ground rod. Lightning likes to find the "shortest route" to earth ground and will typically find a "better path to earth" after 10-20+ feet of grounding cable run (the technical term is cable "impedance" and not just simple cable resistance). The local ground rod provides lightning to earth path, and the 6 AWG cable back to the main home/shed ground rod provides the DC/AC current path to trip breakers and fuses with short circuits.

Clear as mud? 

-Bill

solarhills99

Thanks Bill,

Crystal clear.