I'm supposing there's a good reason for a single ground path:
- Maybe it's about simplicity ensuring certainty.
I am no electrician (or electrical engineer) by a long shot, but I'm always interested to know stuff.
Can any of you "Sparky" experts here, give a simple layman's explanation for this?
And if that's easier said-than-done, then I'll understand that too. But some of us would be interested to know.
Another reason is current flow in the earth .
Different places in the soil can have different potential (think voltage).
You could have positively charged earth (IE +1 volt) near negatively charged earth (-1 volt), with no conductor between them. Now you stick a rod in each one, and connect a wire between them, and you have an effective electric force of 2 volts. Current will flow, and while probably not a huge safety issue, it creates some unpredictability in the electrical system. Magnetically sensitive systems would be affected (analog meters), noise will come out in video and audio systems. It may effect neutral, but I'm not sure. It will also behave as an antenna, and could increase the odds that dangerous transient voltages will be exposed in appliances and devices using the chassis ground during lightning storms, but not by a lot.
But it's also theoretically possible for two different points near each other to be charged with several hundred thousand volts difference. It's impractical to worry about because that much difference in potential would force some ground conductivity to neutralize itself. But that's essentially what lightning is. The ground is one charge while the clouds are another, and when there's enough voltage to make the jump, lightning strikes.
If potential is the same, there could also be a significant difference in ground conductivity between points as close as 50'.
I handled a radio tower site once that was very prone to lightning strikes. We tried several different grounding systems, and eventually the one that worked best was a ring of ground rods around the buildings, all bonded and buried, with all equipment and electrical grounds being bonded to a single point. That didn't solve the lightning, but straightening that out helped our equipment survive more.