Rmc underground

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Old 10-07-18, 05:32 PM
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Rmc underground

How long does galvanized rmc last underground?
 
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Old 10-07-18, 06:27 PM
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Going to depend a lot on the soil conditions like acidity and the condition of the galvanized coating.
 
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Old 10-07-18, 06:49 PM
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Im thinking of updating detached garage wiring. Buried feeder from house is in galvanized installed early 60's.
 
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Old 10-07-18, 07:55 PM
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If you update..... switch to PVC. The conduit will last forever.
 
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Old 10-08-18, 08:21 AM
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My conduit serves as the egc for the garage.

Im sure you need specialized equipment to take an impendence reading on a conduit used as an EGC. ??

However, when I tested with my multimeter... between the ground pin on an outlet in a garage and to the conduit at the point it enters the main panel inside the house it was fluctuating between high impendence reading of 100 ohm>200 ohm.

Again I don't know if that simple test is correct but that would suggest its a bad ground correct?

 
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Old 10-08-18, 09:39 AM
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If you change to PVC..... you'll just add a ground wire in to the pull.
 
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Old 10-09-18, 06:52 AM
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Code doesn't require the resistance test on RMC used as a ground, but it's good you did it. >100 ohm might as well be no ground at all. That pipe or some intermediate connection is significantly rusted and if you reuse it you should pull a separate ground conductor. It's possible the pipe is even partially collapsed at 50-60 years age -- you'll know when you try to pull out the old conductors.
 
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Old 10-09-18, 11:09 AM
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you'll know when you try to pull out the old conductors.

"Try" is the key word, I doubt the conductors will budge.
 
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