Hi all,
I would like to solicit some advice on how to prevent damage in the future and ask for physics lessons on how exactly an earth ground disconnect caused a power surge, and some other issues that came up in today's troubleshooting...
What happened:
Was working on removing foundation near the main panel. Was unaware that part of the buried ground wire from the main was actually surrounded by concrete about 2 ft underground. Not the rod, just some of the excess buried cable (old house, sloppy pour apparently, and sloppy wiring. The excess should have been trimmed, not buried along with the rod...). When the concrete came out, so did the wire, which disconnected from the grounding rod. This apparently caused a power surge to race back up (down?) my electrical system. This in turn fried a bunch of the electronic gear that was connected to a sub panel that had no grounding rod. Subsequent sub-panels all have grounding rods and their circuits experienced no problems:
from main lug to fried sub panel (no ground rod) - 30ft.
from main lug to next ground rod sub panel - 60ft
Questions:
1. Can someone explain (in simple words) why a disconnect in the main's earth ground generated a power surge? I can't wrap my head around the physics. And explain why no breakers tripped, and none of the fuses internal to the fried gear blew either.
2. If the sub-panel that fried had had a ground rod would that have been sufficient to have saved the electronics?
3. We have ground rods at every panel on the property (4 buildings, 5 subs + 1 main), except the one where stuff got fried. It *had* a rod, but it was temporarily disconnected for the foundation work. We had figured that with more ground rods all of another 40ft, 50ft, and 90ft away that the electrons would go thataways instead of frying the stuff under the non-rod sub. Why were we wrong?
4. Do all grounding rods = earth grounds? Not sure that I understand the nomenclature in the threads I've been reading.
5. Do all earth grounds require that the panel connect the neutral to the ground? If so, if I use an ohm meter on such a panel I should get conductivity between the neutral and the ground lugs, right? If I don't have conductivity does that mean that the grounding rod isn't going to work properly? Is there a reason NOT to have the ground rod connected to both the ground and the neutral?
6. We have a persistent 1-3 volts of stray voltage measured on all grounds. It was originally 40 volts but apparently there was a bad circuit that was somehow feeding it. I don't pretend to understand how, all readings of the line showed NO shorts of any sort. Anyway, is 1-3 volts of stray voltage acceptable or should I keep plugging away trying to find the source? If so, what are likely culprits if shorts have been eliminated?
7. We have one of those no-contact voltage detector pens. Inside one of the buildings the pen goes off near almost all metallic objects. I mean everything - completely disconnected BX cables, the individual copper wires therein, simpson strong ties in the ceiling joists, even piles of nails in stud bays. The readings are stronger the higher up vertically the objects are. The same objects, taken out of the building, stop giving readings after a bit. Other similar or identical objects elsewhere do not generate a reading. This was funny at first, but now it's just frustrating, and more than a little creepy. I mean, how would you feel if you thought you finally found where your short was, disconnected the cable, can see *both* disconnected ends, and the pen is still going off like mad?? What the heck could be causing this? And no, there are no large electric motors in operation anywhere near by. And according to my compass, North is exactly where it should be...
Thanks for your time,
-o
I would like to solicit some advice on how to prevent damage in the future and ask for physics lessons on how exactly an earth ground disconnect caused a power surge, and some other issues that came up in today's troubleshooting...
What happened:
Was working on removing foundation near the main panel. Was unaware that part of the buried ground wire from the main was actually surrounded by concrete about 2 ft underground. Not the rod, just some of the excess buried cable (old house, sloppy pour apparently, and sloppy wiring. The excess should have been trimmed, not buried along with the rod...). When the concrete came out, so did the wire, which disconnected from the grounding rod. This apparently caused a power surge to race back up (down?) my electrical system. This in turn fried a bunch of the electronic gear that was connected to a sub panel that had no grounding rod. Subsequent sub-panels all have grounding rods and their circuits experienced no problems:
from main lug to fried sub panel (no ground rod) - 30ft.
from main lug to next ground rod sub panel - 60ft
Questions:
1. Can someone explain (in simple words) why a disconnect in the main's earth ground generated a power surge? I can't wrap my head around the physics. And explain why no breakers tripped, and none of the fuses internal to the fried gear blew either.
2. If the sub-panel that fried had had a ground rod would that have been sufficient to have saved the electronics?
3. We have ground rods at every panel on the property (4 buildings, 5 subs + 1 main), except the one where stuff got fried. It *had* a rod, but it was temporarily disconnected for the foundation work. We had figured that with more ground rods all of another 40ft, 50ft, and 90ft away that the electrons would go thataways instead of frying the stuff under the non-rod sub. Why were we wrong?
4. Do all grounding rods = earth grounds? Not sure that I understand the nomenclature in the threads I've been reading.
5. Do all earth grounds require that the panel connect the neutral to the ground? If so, if I use an ohm meter on such a panel I should get conductivity between the neutral and the ground lugs, right? If I don't have conductivity does that mean that the grounding rod isn't going to work properly? Is there a reason NOT to have the ground rod connected to both the ground and the neutral?
6. We have a persistent 1-3 volts of stray voltage measured on all grounds. It was originally 40 volts but apparently there was a bad circuit that was somehow feeding it. I don't pretend to understand how, all readings of the line showed NO shorts of any sort. Anyway, is 1-3 volts of stray voltage acceptable or should I keep plugging away trying to find the source? If so, what are likely culprits if shorts have been eliminated?
7. We have one of those no-contact voltage detector pens. Inside one of the buildings the pen goes off near almost all metallic objects. I mean everything - completely disconnected BX cables, the individual copper wires therein, simpson strong ties in the ceiling joists, even piles of nails in stud bays. The readings are stronger the higher up vertically the objects are. The same objects, taken out of the building, stop giving readings after a bit. Other similar or identical objects elsewhere do not generate a reading. This was funny at first, but now it's just frustrating, and more than a little creepy. I mean, how would you feel if you thought you finally found where your short was, disconnected the cable, can see *both* disconnected ends, and the pen is still going off like mad?? What the heck could be causing this? And no, there are no large electric motors in operation anywhere near by. And according to my compass, North is exactly where it should be...
Thanks for your time,
-o