Grounding old wiring to detached garage

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  #1  
Old 04-02-14, 07:49 AM
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Grounding old wiring to detached garage

Hello,

I recently bought a house that still has some very old wiring. Knob and tube, old ungrounded 2-wire romex, etc. I had an electrician upgrade my service (new service entrance cable, 200-amp main panel, ground rods, etc), but I am still working my way through the branch circuits.

One of the many issues that I've encountered is that the circuit feeding my detached garage does not seem to be grounded. There is a two conductor cable -- a hot and a neutral -- running through metal conduit between the two buildings. The conduit is buried maybe 6-8" deep. Conductors appear to be stranded 10 AWG. There is an old fused disconnect in the garage.

The only loads, currently, are two garage door openers. The grounding issue came to light when I had a technician over to repair the openers on a rainy day. The floor was wet and he got a bit of a shock while working on them.

Eventually, I plan to run a new cable and install a sub-panel in the garage. Realistically, that isn't going to happen anytime soon. In the meantime, I would like to at least remediate the grounding issue and hopefully add a couple of receptacles in the garage.

My idea is to run new 12-2G NM-B in the house and garage, and then bond the ground wires at each end of the conduit, using the conduit as an EGC. I would replace the disconnect as well. Does this sound like it would be safe and effective?
 
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Old 04-02-14, 07:55 AM
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If the metal conduit is EMT more then ten years old it is doubtful it still provides a complete low resistance path for ground. EMT rusts out when buried.
 
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Old 04-02-14, 09:12 AM
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A better solution would be to pull a green grounding conductor into the pipe.
 
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Old 04-02-14, 09:32 AM
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It's definitely more than 10 years old! Not sure exactly what type of conduit it is. If it counts for anything, it seemed solid when I found it while digging out garden bed in the middle of the yard.

I considered pulling new wire(s), but the pipe seems pretty full and I see no good pull points. If it comes down to that, I would probably be better off just replacing the entire length with new conduit/cable.

I'll take some pictures when I get home this evening to give you guys a better idea of what I'm working with.

Thanks for the responses so far!
 
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Old 04-02-14, 10:29 AM
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Is the conduit threaded or does it have compression fittings on the end?
 
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Old 04-02-14, 11:07 AM
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I want to say it's threaded, but I'll have to double check when I get home.
 
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Old 04-02-14, 07:30 PM
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OK, I confirmed that the pipe is threaded.

I took a bunch of photos and uploaded them to Imgur. You can find the album at http://imgur.com/a/ZQ3GY. Thought this would be better than directly embedded a bunch of photos. I'm happy to do that if it's easier though. Just let me know.
 
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Old 04-02-14, 07:45 PM
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My idea is to run new 12-2G NM-B in the house and garage, and then bond the ground wires at each end of the conduit, using the conduit as an EGC.
But the conduit doesn't enter the garage (buried in the concrete) or the house. The "good" news is it is RMC but the bad news is it must be buried at least one foot and doesn't actually enter either the garage or house. Running new UF-b buried 24" or conduit buried 18" with individual conductors is the only good solution.
 

Last edited by ray2047; 04-02-14 at 09:02 PM.
  #9  
Old 04-02-14, 08:16 PM
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Someone certainly didn't do you any favors with that work.
 

Last edited by ray2047; 04-02-14 at 09:00 PM. Reason: did>didn't
  #10  
Old 04-02-14, 08:26 PM
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That fuse box and the conduit are all junk now. You need to just run a new circuit from your panel using approved wiring methods.
 
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Old 04-03-14, 06:05 AM
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Someone certainly didn't do you any favors with that work.
Tell me about it. That has been a recurring theme so far.

I knew the box was junk but was hoping to save the conduit for the time being. Thought I could pull bare copper through the wall of the house. Forgot the conduit wasn't exposed in the garage until I took another look for the photos.

Oh well. New circuit it is then. That was always the long term plan, just gonna have to move it up on the list. Still gonna have to wait at least until Fall though. GF will kill me if try to dig up her garden beds now.
 
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Old 04-03-14, 06:37 AM
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Plan B: <Warning GF May Complain of how it looks> You could run UF-b over head supported by a messenger wire and then bury in the fall.
 
  #13  
Old 04-04-14, 07:59 AM
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That's not a bad idea. Neither of us want an overhead wire in the middle of the yard, but it wouldn't be the end of the world if it's just for a few months.
 
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