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Old 09-17-2011, 03:45 AM   #16
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Grounding question for subpanel


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Originally Posted by brric View Post
I think it's unlikely but I was wondering if it is LFMC.
Even if it was, it would not help. The conduit is over 6 feet, so it cannot be an EGC. 250.118(6)

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Old 09-17-2011, 03:49 AM   #17
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Grounding question for subpanel


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Nuts and fittings without teeth can also provide a bond, although whether or not they do is harder to determine. If the gray paint is scraped off where other metal parts are attached then the likelihood of (successful) bonding is greater.

A conduit formed from a spiral with edges that physically lock together to achieve the cylindrical shape (water can soak in) is usually not an acceptable equipment grounding conductor. An additional conductor which can be an aluminum strip, running through a flexible conduit, makes the conduit into an acceptable EGC when the strip is bonded at the ends in an approved fashion that does not in all cases require wire nutting with other ground wires.)
AC cable is not listed for wet locations.320.12
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Old 09-17-2011, 09:48 AM   #18
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Grounding question for subpanel


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Even if it was, it would not help. The conduit is over 6 feet, so it cannot be an EGC. 250.118(6)
I understand that but it would be a compliant raceway if it contained an equipment grounding conductor.
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Old 09-17-2011, 09:53 AM   #19
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Grounding question for subpanel


Thanks for all the thoughts. But, I'm more confused than ever.

I can't really replace the underground wiring at this time. And, it's been supplying power to the barn for years, so it works at least.

But, how do I ground the panel? Do I bond the neutral and ground? Do I leave the local ground rod attached?

BTW, where is the "water" coming from? The FMC is encased in plastic pipe (conduit) - unless the plastic leaks, it should be dry in there (?)

Eric

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Old 09-17-2011, 04:26 PM   #20
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Grounding question for subpanel


Materials used for buried power lines has to be waterproof because there is no way of knowing whether a frost heave could crack the outer PVC pipe.

Leave the ground rod bonded to the subpanel.

(sigh) On second thought I would pretend that the conduit was a sufficient EGC and bond it to both main panel and subpanel and take a chance it works.
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Old 09-17-2011, 04:30 PM   #21
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Grounding question for subpanel


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BTW, where is the "water" coming from? The FMC is encased in plastic pipe (conduit) - unless the plastic leaks, it should be dry in there (?)
The NEC considers locations outside and underground to be wet areas.
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Old 09-17-2011, 07:27 PM   #22
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Grounding question for subpanel


What type of insulation is on the conductors?
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Old 09-18-2011, 11:18 AM   #23
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Grounding question for subpanel


I can just barely read the writing, but the wires say USE-2. As I said, there are three of these in the metal conduit (BX?).

Is this okay for underground? Can I use the conduit as a 4th conductor?

Thanks
Eric
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Old 09-18-2011, 12:55 PM   #24
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Grounding question for subpanel


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I can just barely read the writing, but the wires say USE-2. As I said, there are three of these in the metal conduit (BX?).

Is this okay for underground? Can I use the conduit as a 4th conductor?

Thanks
Eric
Use-2 is fine for underground.

No, you cannot use the this type of conduit as a ground here nor can that conduit be used underground.

How long is the run to the barn?

How badly do you want to keep the phone line?
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Old 09-19-2011, 11:29 AM   #25
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Grounding question for subpanel


The distance from house to barn is about 100 feet or so.

As for the phone line, are you thinking it should be used as a ground wire? Too small in gauge?

As for the conduit, the construction of this appears to have a continuous band of aluminum, with no gaps, in a spiral from barn to house. So, I'm wondering why it could not serve as a ground conductor. It's not made of discrete links.

Eric
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Old 09-19-2011, 11:40 AM   #26
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Grounding question for subpanel


The phone line may not be used as a ground wire.

Certain kinds of flexible conduits made from a spiral can oxidize in a fashion that any current that happened to get into that conduit goes 'round and 'round instead of skip from one turn of the spiral to the next. When the current is large and goes 'round and 'round it can cause overheating particularly if the metal strip of the spiral is of quite thin metal. Under normal conditions no current flows through "the ground wire" or "the conduit itself" (EGC). The EGC is there just in case a defect causes exposed metal including that of an appliance to become energized in which case grounding keeps the voltage difference between the say washing machine and the say damp basement floor from being high enough to electrocute someone.
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Old 09-19-2011, 11:41 AM   #27
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Grounding question for subpanel


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The distance from house to barn is about 100 feet or so.

As for the phone line, are you thinking it should be used as a ground wire? Too small in gauge?

As for the conduit, the construction of this appears to have a continuous band of aluminum, with no gaps, in a spiral from barn to house. So, I'm wondering why it could not serve as a ground conductor. It's not made of discrete links.

Eric
No, I am not thinking of using the phone line as a ground.

The conduit cannot be used as a ground, because if there was a ground fault(short) the conduit may not be good enough to trip the breaker.

If this was an AC cable it would be different. But AC cable cannot be underground.

The conduit needs to be removed, it is a hazard. Basically pull it off and leave the wires.

You have 2 choices:

pull a ground wire and keep the phone line.

remove the phone line and use only the 3 existing wires.

The water line is PVC so that is not a problem.

You still need another ground rod at barn, 1 is not enough.


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