3 wire subpanel needs ground back to main?

Old 05-11-17, 11:07 AM
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3 wire subpanel needs ground back to main?

Hello. I've researched this all day and need some advice. I have an attached garage with an unused junction box wired with 2 hots and a neutral. I'm guessing that pre 2008 the previous owner must have intended to add a sub panel but never did.
It is fed from the main panel on a 30 amp 2 pole breaker. It's comes through the attic with #10 wires in metal conduit. I tested it and have good voltage. It seems like a perfect situation since I wanted to add a couple new 15a circuits by means of a very small sub panel.
Running a ground back to the main is very difficult since it passes through a long cramped attic and access to the knockouts in the main panel would be impossible.
What are the easiest and best NEC approved options?
Would two grounding rods and bonding neutral and ground bars to the sub panel be safe?
Could I jumper onto a ground wire from a diffident jbox in the attic to run to the sub panel?
Use the cold water line in the attic? Could I assume the metal conduit is grounded to the main panel?
Thanks in advance.
Old 05-11-17, 11:33 AM
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Join Date: Mar 2006
Location: USA
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If the metal conduit is uninterrupted that is your ground.
Use the cold water line in the attic?
No. For EGC you need a reliable low impedance path. A metal water pipe can't be trusted for that purpose for multiple reasons and is not code compliant.

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