repair of severed flexible metal conduit

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  #1  
Old 03-22-07, 06:15 AM
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repair of severed flexible metal conduit

While doing some non-electrical repair work on the house (using the Sawzall with a 12" blade), I accidently severed a flexible metal conduit ("Greenfield") and the wires inside it. I immediately turned off the circuit breaker and have since removed the severed wires from that conduit.

My plan is to join the severed conduit with couplings and then pull new wire. There would be no hidden wire splices or hidden junction box. The location of the damage is in a difficult to reach joist space between floors. I had to take "heroic" measures to gain access to the damage location.

I would use 2 EMT-to-flex combination couplings (like the one here: http://www.aifittings.com/b_9.htm#860) with a short piece (2"-3") of EMT conduit between them--thus making this run of conduit slightly longer than original.

Is there any reason why I can't or shouldn't make this kind of repair? If so, alternatives?

thanks,
Brent
 
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Old 03-22-07, 09:03 AM
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To make this a code compliant installation, we need to know if you have flexible metal conduit or greenfield -- they are two different materials. Greenfield cannot be spliced or pulled with new conductors as you suggest. Flexible metal conduit can be joined using the appropriate FMC connectors and a short piece of new FMC (not EMT). Is there any way you can upload a picture to a free photo site and post a URL? Or perhaps provide the OD measurements of the metal sheathing?
 
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Old 03-22-07, 10:48 AM
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I had thought flexible metal conduit and Greenfield were synonymous (referencing my copy of Wiring Simplified, 40th edition) but there is apparently some other distinction here that I was not aware of. I'm always willing to learn something new though.

I'll try to describe the conduit attributes. The house was built and wired in the mid-60s. All the wiring goes thru runs of flexible helical steel (a magnet sticks to it) conduit. The outside diameter of the conduit measures about 7/8"--in other words, it looks like a 7/8" hole minimum would have to be drilled in a 2x4 for it to pass thru. The inside diameter of the conduit measures about 5/8". I think this qualifies as 1/2" conduit. I have a 1/2" screw-in connector here that screws into the end of the conduit and seems to fit well. It seems that the conduit was laid out empty/wireless and then wire pulled thru it--I assume this only because looking at the service panel where all the wires enter the conduit connections, there is a variety of wire color combinations at the conduit entry points. But I guess it could have been pre-wired conduit--in case that is an important distinction.

Assuming this is FMC and it can be spliced, I have not been able to find a coupling that would join two ends of FMC (except for the screw-in type coupling (<http://www.doityourself.com/invt/u232223>) --but that wouldn't work here because both ends of the conduit are in fixed positions and can't be twisted).

Anyway, I hope that helps to determine what type of conduit this is.

BTW, I have a picture that I will post in the meantime if I can find one of those photo-posting sites.

thanks,
Brent
 
  #4  
Old 03-22-07, 11:44 AM
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photo posted

I snapped a photo of one end of the conduit. I hope this URL works for viewing:

<http://new.photos.yahoo.com/north_sea_brent/album/576460762394681615/photo/294928804290910998/0>

Brent
 
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Old 03-22-07, 03:10 PM
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where I come from FMC and greenfield are used synonomously. I was told that Greenfield used to be a manufacturer of FMC.

To install an internal coupling, you would screw it into one of the ends. Then take the free end and twist it (CW as you look into the end). Unless the piece is very short, you can get 3 or 4 turns. Then place it on the coupling and screw it on.

as a matter of fact, if you go to this site, you can see that Greenfoeld is FMC

http://www.jsvtech.com/tite-greenfield.html
 
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Old 03-22-07, 03:22 PM
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You're right that Greenfield and FMC are interchangeable. Some people (including my co-workers) errantly call any old metal sheathed cable or conduit "greenfield". I'm always suspicious that someone says "greenfield", but they really have some type of armored cable like BX.

You can add a new section of FMC and pull conductors in. I believe there is a squeeze-to-squeeze coupling for FMC, but I'm having trouble finding a link. You can use screw-in couplings by twisting the end of the new piece of conduit to engage the coupling without twisting the existing FMC.

I suppose you could transition to EMT, but EMT should really be supported by clamps to framing members. The fittings between the flex and EMT are not supposed to be supporting the "dangling" piece of EMT. If you go this route, you could frame in a 2x2 with a half-strap or something similar to support the EMT.
 
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Old 03-22-07, 03:33 PM
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something else I have done. Honestly no idea if it is legal or not but never has an inspector ding me on one.

Use 2 external FMC connectors and couple them using a rigid coupling.
 
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Old 03-22-07, 06:00 PM
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ADD: Make sure to pull in a ground wire!
 
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Old 03-23-07, 08:51 AM
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Well, I'll be darned...I was able to easily get enough twist in one end of the FMC to allow it to screw itself in to the internal/screw-in coupling on the other end. (Funny...I never even thought to try that.) I now have a properly repaired conduit.

I have already pushed the fish tape thru and have attached the cluster of new wire to the end (including a brand new ground wire). Now I just have to wait for a buddy to stop by later today and help feed the wire thru.

thanks much everybody,
Brent
 
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Old 03-23-07, 09:00 AM
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Use cable lubricant on the wires, especially if the distance is great. Make sure that it is cable lube. Vaseline, hand creams and other greasy items may work, but they can (or will) damage the wires, so don't use anything except cable lube.

Also, make sure that there are no sharp edges on either end or at the connection in the middle to damage the wires.
 
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Old 03-23-07, 03:16 PM
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Well, I'll be darned...I was able to easily get enough twist in one end of the FMC to allow it to screw itself in to the internal/screw-in coupling on the other end. (Funny...I never even thought to try that.) I now have a properly repaired conduit.
================

I would say "that's why we get the big bucks" but it's more of the "how do I fix this screw up" thing.

If you make enough mistakes, you end up knowing how to fix just about anything.

glad to hear it worked out for you.
 
  #12  
Old 03-25-07, 08:44 AM
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Before pulling the wire, I picked up a bottle of legitimate cable lube at the same place where I get electrical parts. There was a bit of a hang-up getting past the conduit splice because the loop in the end of the fish tape was slightly wider than the inside diameter of the screw-in couplings, but after working it thru that point it went pretty smoothly with all the 50' spools just about empty now (~40' conduit run). It's not hooked up yet but there is plenty of extra wire on each end to finish things.

Brent
 
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