Repair to damaged 3" RMC

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tom baker

tom baker

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Master Electrician
Contractor was saw cutting 8" thick concrete road, there was 3" RMC just below the bottom of the concrete. cut thru 1/2 of the RMC and that feed two traffic signals across the road. Pull out all the old rubber insulated wires, cut the conduit, repair, repull new - worked from 2 pm to 10 pm to get the signal back. Pulled about 1,000 feet of muilticonductor cable.

We use two rigid compression couplings - take the mallable one and grind out the nubs in the center so it can slide over the undamaged section and then slide back onto the new conduit. You can't do this with steel compression couplings as there center nub is a ring that goes all the way around

Does any one make a hinged split coupling - similar to a plumbing repair band?

And yes the conduit was located. Why was it so shallow? There was a foundation it went over if you look at the picuture you can see the angle of the old section on the left.
 

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infinity said:
What's wrong with the current repair?
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The mallable fitting on the left is non stock, we order them in and modify to keep on hand. This repair was tough as the two ends of the 3" are about 20 degrees out of alignment.
I would like to find a fitting we don't have to file out the center nib.
 
Our current standard is sch 40 pvc with concrete encasement. This was repair where we needed to match the RMC. We could of used a pair of compression connectors, PVC FAs and PVC, but using the rigid compression coupling is straighforward - esp if you have them on hand ahead of time.
 
infinity said:
I was thiking of a split-coupling too but can those be used in wet locations? And aren't they required to be connected to a thread?
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The repair, as made, won't offer any protection from damp or wet conditions either. The repair section would have to have a kick in it to get the couplings going straight for them to make a tight seal.

Ultimately, I think I would have looked into getting the slit in the pipe brazed as a repair. It would have made for a better seal and overall integrity of the conduit would have been maintained. As it is now, there's no integrity to the repair.

Edit to add: Sorry, I didn't notice that there was a coupling in the original run. This run was probably never sealed properly :(
 
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PetrosA said:
... This run was probably never sealed properly :(
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How do you seal couplings in rigid conduit? They are straight thread couplings and do not make a mechanical seal like the plumbing pipe where both the coupling and pipe have tapered threads.
 
don_resqcapt19 said:
How do you seal couplings in rigid conduit? They are straight thread couplings and do not make a mechanical seal like the plumbing pipe where both the coupling and pipe have tapered threads.
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True, but electrical conduit isn't generally subjected to the same pressurized wet conditions that plumbing pipe is. Completely submerged it might seep water, but a tight connection (needed for ground continuity, right?) is pretty water tight in my experience. Aside from water tight or not, the way that coupling was installed as an offset couldn't have been kosher the first time around...
 
PetrosA said:
True, but electrical conduit isn't generally subjected to the same pressurized wet conditions that plumbing pipe is. Completely submerged it might seep water, but a tight connection (needed for ground continuity, right?) is pretty water tight in my experience. Aside from water tight or not, the way that coupling was installed as an offset couldn't have been kosher the first time around...
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It is my experience that threaded conduit connections leak. If you install vertical conduit in a wet location the water will run down the outside of the conduit and hit the coupling. It will sit in the small space between the conduit and the coupling and slowly work its way around the threads and into the conduit.
Many years ago the Candian code required tapered thread couplings on their conduit. I had a discussion about this with a rep from Allied Tube at a trade show. She told me that they had a lot of complaints for conduits "leaking" after the switch was made from the previously required taperd thread couplings to the newly permitted straight thread couplings. They do have testing that say straight thread couplings are suitable for grounding, but it is my opinion that a tapered thread coupling would be a lower resistance connection as there would be greater contact pressure between the male and female threads.
 
tom baker said:
Contractor was saw cutting 8" thick concrete road, there was 3" RMC just below the bottom of the concrete. cut thru 1/2 of the RMC and that feed two traffic signals across the road. Pull out all the old rubber insulated wires, cut the conduit, repair, repull new - worked from 2 pm to 10 pm to get the signal back. Pulled about 1,000 feet of muilticonductor cable.

We use two rigid compression couplings - take the mallable one and grind out the nubs in the center so it can slide over the undamaged section and then slide back onto the new conduit. You can't do this with steel compression couplings as there center nub is a ring that goes all the way around

Does any one make a hinged split coupling - similar to a plumbing repair band?

And yes the conduit was located. Why was it so shallow? There was a foundation it went over if you look at the picuture you can see the angle of the old section on the left.
Click to expand...

http://www.bptfittings.com/catalog/CatalogFamily.aspx?CategoryId=10&FamilyId=698
http://www.emersonindustrial.com/en...ed_Rigid_Conduit_IMC_Couplings_Connectors.pdf Page 6


Killark or Appleton used to have one, also for threaded conduit. It was a split/cast piece with 4-6 bolts on each side.
 
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