Fiberglass Sweep

[charlie b]

It is common for specifications to require that when an underground ductbank turns up towards the electrical room, the 90 degree sweep is to be done with rigid steel conduit, even if the rest of the conduit is PVC. First question: why? I am told that it is because the process of pulling cables can cause damage to PVC at that final bend, and that the rigid steel is used to provide higher strength. Second question: does that make sense?

Now the real issue. An EC elected to use some type of reinforced fiberglass material, instead of rigid steel, for the 90 degree sweep. We (the designers of record) are being asked to approve the substitution (after the fact, of course). Third question: has anyone seen this before, and if so is it better or worse than the rigid steel?

 

[jcormack]

Charlie, yes the reason steel is used in the 90s is because the friction & the constant rub during the pull can eat a hole into the PVC. The fiberglass manufacturers claim that the fiberglass 90s don't have the same problem due to higher temp rating & less friction - I still use metal sweeps. The fiberglass is great for long straight runs though, one person can carry a 20 ft 4" pipe.

 

[ActionDave]

It is common for specifications to require that when an underground ductbank turns up towards the electrical room, the 90 degree sweep is to be done with rigid steel conduit, even if the rest of the conduit is PVC. First question: why? I am told that it is because the process of pulling cables can cause damage to PVC at that final bend, and that the rigid steel is used to provide higher strength. Second question: does that make sense?

It's the friction from the rope or a pull string that cuts through the ninety. If you have ever seen anybody cut a piece of PVC with a mason twine that's what happens to the final PVC ninety.

Now the real issue. An EC elected to use some type of reinforced fiberglass material, instead of rigid steel, for the 90 degree sweep. We (the designers of record) are being asked to approve the substitution (after the fact, of course). Third question: has anyone seen this before, and if so is it better or worse than the rigid steel?

I've never used fiberglass but I think it would be just fine. PVC is plenty tough enough for the job it has to do underground, I imagine fiberglass is at least as tough or tougher. I would use them it they were available off the shelf from my supply house.

 

[ptonsparky]

We have used large radius fiberglass elbows for long pulls with no problems.

We also use steel cable for our pulls, conduits are oversized and up to 1/4 mile in length.

Not a scientific comparison.

You only cut a pvc 90 with a pull rope once, unless you are really trying to prove how stupid you are.

 

[augie47]

The fiberglass elbows are gaining in popularity in this area. Seemingly work well.
Told they are slightly more expensive than steel but no corrosion and no bonding.