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How hard is it to pull larger wire through 120 ft of FMC using existing wire?

How hard is it to pull larger wire through 120 ft of FMC using existing wire?

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  #1  
Old 11-14-12, 09:48 PM
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How hard is it to pull larger wire through 120 ft of FMC using existing wire?

I have two 120 ft FMC 240V runs in the attic where I'd like to run larger wire (8awg to 6awg) in one of them, and add a ground wire to the other. The FMC conduits are 3/4" and 1".

My idea is to use the old wires to pull through the new one -- tape them together and apply lube. I would plan to do one wire at a time, not the whole bundle. There is a gradual 90 degree bend in the conduit near the roof header where it drops down to the main panel. Otherwise the conduit is pretty straight.

Before I buy all the wire and actually try this out... how hard is this generally for this distance? I have never tried this before. Am I going to find out that it is impossible to pull so the tape would just come apart?
 
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  #2  
Old 11-14-12, 10:09 PM
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The FMC conduits are 3/4" and 1".
Flexible metal conduit as in what.....seal tite or what looks like large BX ?

Extremely tough if not impossible to pull wire thru that long of a flex run.
 
  #3  
Old 11-14-12, 10:19 PM
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It's BX conduit.

Maybe I should cut it off where it enters the attic from the panel, pull out the wires, and replace it with EMT, I wonder if that would be easier overall.
 
  #4  
Old 11-14-12, 10:25 PM
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It's BX conduit
Actually if you are going to use trade names it is Greenfield if it is conduit. BX is cable and you can't pull new wires through BX.
 
  #5  
Old 11-15-12, 01:01 AM
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As Ray stated, BX is a manufactured cable and you cannot pull the existing conductors and replace them with anything. Look carefully at the wires, do they appear to have an overall paper wrapping inside the "conduit"? If yes, then it is BX and not conduit and you are SOL.

On the other hand, if it IS flexible metallic conduit (Greenfield) then you should be able to replace the wires. The 3/4 inch FMC will hold four #6 type THHN/THWN conductors and the 1-inch will hold six conductors of the same size and type.

Do NOT attempt to pull the wires individually but first pull out the existing wires and then pull in the new wires as a complete set. You may use a strong cord (twine) taped to the old wires as a pulling rope for the new wires. 120 feet is a long pull and you should use a wire pulling lubricant.
 
  #6  
Old 11-15-12, 06:21 AM
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Thanks, good tips Furd. It is FMC (Greenfield), not BX. In the main panel there is the end piece with locknut that makes the opening to the 3/4" conduit a bit smaller. Would it still fit four #6 typically, without removing the locknut? The 1" conduit already has 3 wires for another circuit (6 total) so I was planning to leave those inside and replace the other 3 in with 4 new ones that conduit (7 total with ground), if possible.
 
  #7  
Old 11-15-12, 07:25 AM
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Not to discourage you but flexible conduit can be extremely uncooperative, especially at that length. I have had problems with 8' lengths. The infeed end needs to be securely clamped down with no slack. You will need a second person to feed the cable. Don't rely on just tape to hold your pulling line, put a loop in one wire and tie it on, tape the bundle tightly in a few places for the first 3'. Tape a smooth round nose on the bundle. Keep slopping on the lube as you feed. Sometimes you can sail right through, sometimes not. Trying to pull with existing wire in the conduit is very tough. Good luck.
 
  #8  
Old 11-15-12, 07:45 AM
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As Toolman says, Greenfield is not that easy to pull through, especially if it has any slack in it. All it wants to do is flex and contract. This makes it hard to pull even when new.
 
  #9  
Old 11-15-12, 06:54 PM
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I wouldn't attempt it, but if I were, I'd use a pulling grip like this.

Mesh Grips - Electrical Tools - Hand Tools - Grainger Industrial Supply
 
  #10  
Old 11-15-12, 07:31 PM
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Using a fish tape and a pulling grip, I would think it could be done, depending on the age of the conduit. Use the old wires to pull in the fishtape when pulling them out.

I suggest using a stranded #10 ground
 
  #11  
Old 11-16-12, 12:23 PM
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The 1" conduit already has 3 wires for another circuit (6 total) so I was planning to leave those inside and replace the other 3 in with 4 new ones that conduit (7 total with ground), if possible.
That is almost certainly not possible, because the wires will be crossed inside the FMC. It would be a bear even if they weren't, because of the friction.

If you're careful, you may be able to replace all of the wires with a full new set. Pull from the easy-pulling end (the one that inside of the spiral points toward and the outside of the spiral points away from). I would tie poly pulling line onto the old wires and pull that in, then use that to pull a strong 1/4" rope in, and use that rope to pull the new wires in.

Make the head both smooth and strong - staggering or daisy-chaining the wires helps with that - and have the person feeding fill the pipe with clear lube before you start. Also keep the wires in the bundle from crossing as they enter the pipe, and keep coating the bundle with lube for at least the first 50 to 75 feet. Add lube after that, just not as heavily.
 

Last edited by Nashkat1; 11-16-12 at 07:50 PM.
  #12  
Old 11-16-12, 04:49 PM
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I did not catch that part Nash.

Max #6's in a 3/4" FMC is 4 and max in 1" is 7.
 
  #13  
Old 11-16-12, 06:44 PM
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Make the head both smooth and strong
There will be the problem and especially for a DIYer. The flex already has wires in it so there isn't much room left for the head which may need most of the inside of the flex. That's why I suggested a pulling grip.
 
  #14  
Old 11-16-12, 07:58 PM
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The flex already has wires in it so there isn't much room left for the head which may need most of the inside of the flex. That's why I suggested a pulling grip.
Right. That's why I suggested that
Originally Posted by Nashkat1 in post #11
If you're careful, you may be able to replace all of the wires with a full new set. Pull from the easy-pulling end (the one that inside of the spiral points toward and the outside of the spiral points away from). I would tie poly pulling line onto the old wires and pull that in, then use that to pull a strong 1/4" rope in, and use that rope to pull the new wires in.
 
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