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Early 1960's home. 200-amp main service panel on first floor. 3-wire (L-L-N) feeder to 100-amp sub-panel in the second floor attic, about 25-30 feet from the main service panel.

Neutral and ground bonded at main service panel. I have 2 grounding rods on opposite sides of the house, more than 10 meters apart. One conductor connects at the service meter and the opposite conductor at the main service panel (located in middle of house).

Sub-panel does not have a grounding conductor. Neutral and ground are bonded and NOT grounded to the sub-panel box.

Am I safe? The lack of a grounding conductor from the sub-panel makes me uncomfortable.

Possible options?

  1. Leave it alone.
  2. Run a grounding conductor from sub-panel to the main service panel. This might be possible, but will be difficult at best. Also separate neutral and ground at sub-panel. Install ground bus bar and bond to sub-panel box. Right?
  3. Run a grounding conductor from sub-panel to main service panel grounding rod. Leave the rest alone. This is easier. Is it safe?
  • Is the feed from the main to the sub in conduit? – longneck Dec 20 '18 at 19:59
  • Is the existing feeder for the subpanel run using a cable, or in conduit? – ThreePhaseEel Dec 21 '18 at 1:21
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Option 2 is the only one that will improve safety here.

A single wire break should not create a dangerous condition. But that is exactly the situation you have, because every circuit in the subpanel has a bootlegged ground. If that neutral wire fails to make good connection, the ordinary loads in the subpanel will "pull the neutral hot". That normally wouldn't be a big deal. But because all those grounds are bootlegged, it will ”pull all the grounds hot” too. So now switchplate cover screws or the panel cover itself can bite you.

By trying to put on grounding theater, the last guy made things worse than no grounds at all. Worse, Code once endorsed this, and still does where dryer and range sockets are concerned.

Now you don't have to go back to the panel. It will suffice to reach the grounding electrode system, i.e. The bare wire running to those two ground rods.

  • Follow up question: Can I separate ground and neutral on the sub-panel and run a grounding conductor from the sub-panel ground bus directly to the same grounding electrode that is connected to the main panel bonded neutral-ground? – Richard Whitehurst Dec 20 '18 at 18:53
  • Ah! I believe you already answered my follow up question. My sub-panel GEC does NOT have to go back to the main panel. It DOES have to connect to the grounding electrode system. – Richard Whitehurst Dec 20 '18 at 19:03
  • If he chooses the option to run a ground wire to the grounding electrodes instead of the main panel, then neutral and ground in the subpanel should remain bonded? – PhilippNagel Dec 20 '18 at 19:13
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    Not bonded. Neutral to neutral as already in place. Ground to grounding electrode ties it in a safe way to all the other grounds in the house. Only one bonded location per building. – manassehkatz Dec 20 '18 at 21:42
  • Yes. Thanks to all. Confirmation that bonded neutral-ground in the subpanel is a problem. This is what prompted me to find a fix in the first place. – Richard Whitehurst Dec 20 '18 at 22:10

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