Years ago, 1976 to 1990, the telephone industry went from old analog mechanical equiptment to digiatl computer to do the calling, billing and offer a lot of features we now know as standards. The conversion process and the debugging took a lot of work and energy as well as dicovering some new ways to get the job done without problems, grounding being a big factor in noise and problem prevention. All the phone companys I know of use banks of batterys to power the equiptment offices, we used commercial power ran through inverters to charge the batterys but all the equiptment drew its power from the battery banks. The reason I'm clarifying this is all power, voltage and amperage, comes out of ALL batterys from the negatve battery post and travels through the circuit and returns back to the positive post My main point is we had to convert our grounding(positive side) in the offices from conventional to perephial grounding, we had copper buss bars aroud two to three inches tall by 1/4 inch thick, depending on the office size and the power used, running all the way around the equiptment in the offices with multiple 000 or larger ground wires hook to them We lived in the Mojave Desert in SO CA and the summer thunderstorms could wreak havoc with the digital offices through the air and telephone lines Noise can be induced from many sources into digital devices is my message. You can never have to good of a ground on any thing using electrical power to run digital devices IHTHs someone