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Reroute old wiring: Fabric-insulated, two hot, one neutral in 3/4" EMT?

Reroute old wiring: Fabric-insulated, two hot, one neutral in 3/4" EMT?

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  #1  
Old 11-02-10, 04:32 PM
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Reroute old wiring: Fabric-insulated, two hot, one neutral in 3/4" EMT?

Hey all. Great forum. Looking for a little help....

I am rerouting some 3/4" EMT in my attic crawl space so that I can install a couple skylights. My house was built in 1947 and has been updated more than a couple times before I purchased it last year. My attic is like a spider's web of conduit and romex going seemingly in every direction.

The conduit that I'd like to reroute has three wires in it, all of which are fabric-insulated (old!), 14-gauge. At the junction box where I determined this, as far as I can tell there are two hot (black) and one neutral (white) wire. No ground wire is apparent. I tested all three wires with a non-contact voltage detector to verify. The detector goes crazy when in contact with the two black wires and stays silent when touching the white.

I plan to install a new junction box to connect a new run of wire that travels around my skylights inside new 3/4" EMT that eventually reconnects with the original conduit at a second junction box, once clear of the skylights.

1) Does the two hot/one neutral inside one conduit make sense given the age of my house? Am I missing something? There isn't anything requiring 220 anywhere near that side of the house, though perhaps at one time there could have been...

2) What wire should I use to make the new run? I assumed I would be using 14-2 but now that doesn't make sense. Would 14-3 be appropriate?

Thanks for your help!
 
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Old 11-02-10, 05:22 PM
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Best to determine for sure if it is in use and where it is in the breaker box. If not used then disconnect at the breaker box and abandon. If in use best practice is run new cable or THWN if you use part of the existing conduit.

By code ungrounded wiring can not be extended. Whether the existing conduit meets the grounding requirement would need to be determined. Even perhaps more critical is if insulation that old would hold up to manipulation needed for moving it.
 
  #3  
Old 11-02-10, 06:02 PM
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Where do you live? I ask because conduit in a residence is uncommon, even for a home built in 1947 except for a few places such as Chicago or New York City. It could be that all the non-metallic wiring is a code violation.

Fabric (or cloth) covered wire is in reality rubber insulated with a thread overlay, usually a minimum of two threads wound in opposite directions. It has been my experience in buildings a whole lot older than your home that when protected from the ravages of oxygen (which is detrimental to the rubber) the insulation on such wires is usually of acceptable quality. This means that the wire inside the conduit is probably not a hazard although where it is in junction boxes and the first six to twelve inches into the conduit may be completely rotten. Left untouched it probably isn't a danger but since cutting back the conduit a foot or so is generally not an option it is generally necessary to replace the entire run in the conduit if any repairs are made.

Now what you describe as "two hots and a neutral" is most likely what is called a Multi-Wire-Branch-Circuit or MWBC for short. It is a completely acceptable method of running two 120 volts circuits or a combination 240/120 volt circuit. If you are not limited by local codes to using conduit you can use type NM-B cable to do what you propose IF the conduit is properly grounded. If the circuit is now wired with #14 conductors then that is the proper wire to use but you need to verify that the fuse or circuit breaker for this circuit is no more than 15 amperes. If you use conduit then individual wires with type THHN insulation is far preferable to using cable inside the conduit.
 
  #4  
Old 11-03-10, 09:11 AM
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Thanks guys.

Furd: I live in Denver FYI.

Describing my situation in a little more detail:

I have access to where the conduit run ends at one end only. It terminates at a double-stacked junction box and the circuit continues from there via more modern means (NM-B WITH ground). The other end uses a 90-degree elbow to send the conduit to the lower floors of my house without any junction boxes present before making that turn downward and disappearing out of sight. I suspect attempting to replace the conduit in its entirety would require ripping walls and floors apart. There's no easy access given how many times this house has been remodeled since '47.

My panel is located on the outside of my detached garage, about 75 feet away from where service enters my basement, underground. Replacing this wire all the way back to the panel is beyond my means. At some point I hope to trench the back yard and have the wiring in my entire home updated, but that's many months and many dollars in the future.

Would I be able to cut the conduit at the end w/o a box, install a new junction box there where I splice in the new nhhb wire and run it via new conduit to the existing junction box at the other end? If that's not permissible is there a way to make it such without replacing the entire run of conduit?

To make matters worse I suspect cutting and reconnecting the old conduit will be tricky without cutting the wire at the point of the new junction box...

Suggestions?
 
  #5  
Old 11-03-10, 10:07 AM
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Originally Posted by MAFreeze View Post
I suspect attempting to replace the conduit in its entirety would require ripping walls and floors apart. There's no easy access given how many times this house has been remodeled since '47.
There's no reason to replace the conduit, you just need to find the accessible junction box where the conduit terminates on the lower floor and repull the conductors from there.

Would I be able to cut the conduit at the end w/o a box, install a new junction box there where I splice in the new nhhb wire and run it via new conduit to the existing junction box at the other end?
That would be the best way. You'd use #14 THHN wire in black, red and white. You can use the metal pipe itself as the ground if it is installed correctly or pull a green #14 along with the others.

To make matters worse I suspect cutting and reconnecting the old conduit will be tricky without cutting the wire at the point of the new junction box...
Cutting the wire is fine because you will be replacing it back to the next junction box anyway. An additional 30' of #14 THHN is about $3, so not worth saving the old rubber wire that's nearly junk anyway.
 
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