RMC and Schedule 40...interchangeable ?

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conmgt

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Hello,

This has likely been asked before but I didn't find it.

I need some 3" threaded RMC and a local company offered to sell me cut and threaded 3" Schedule 40 pipe that was quite a bit less expensive per foot than RMC. The company didn't seem to see what difference it would make if I used their Schedule 40 vs. RMC.

Are RMC and Schedule 40 interchangeable ?
 
conmgt said:
Hello,

This has likely been asked before but I didn't find it.

I need some 3" threaded RMC and a local company offered to sell me cut and threaded 3" Schedule 40 pipe that was quite a bit less expensive per foot than RMC. The company didn't seem to see what difference it would make if I used their Schedule 40 vs. RMC.

Are RMC and Schedule 40 interchangeable ?
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No. Not directly. Guessing you mean sch 40 pvc.

That said, depending on job specs and the type of job conditions you may be able to use it instead.

I can bury both of them, but can’t expose the sch 40 to damage.
 
I thought it was sch40 pvc.
And no, you can’t substitute schedule 40 steel pipe for RGS.
 
tkb said:
I thought it was sch40 pvc.
And no, you can’t substitute schedule 40 steel pipe for RGS.
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He said RMC, not RGS. And as far as suitability goes, the black iron pipe is probably fine, if not better, than RMC, aside from any listing issues. It's designed to hold pressure. Not so much the other way around.
 
gadfly56 said:
He said RMC, not RGS. And as far as suitability goes, the black iron pipe is probably fine, if not better, than RMC, aside from any listing issues. It's designed to hold pressure. Not so much the other way around.
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From what I have read, listed RMC has a smoother inside surface than regular pipe. Pulling wire through regular pipe may damage the insulation. Also, conduit is intended to be bent without cracking or bending. Sched 40 pipe may not bend so well.
 
K8MHZ said:
From what I have read, listed RMC has a smoother inside surface than regular pipe. Pulling wire through regular pipe may damage the insulation. Also, conduit is intended to be bent without cracking or bending. Sched 40 pipe may not bend so well.
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You make some excellent points. It would be interesting to know the interior surface roughness for the two.
 
gadfly56 said:
You make some excellent points. It would be interesting to know the interior surface roughness for the two.
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I just recently looked at some black iron and galvanized plumbing pipe nipples, and they have a very noticeable ridge on the inside with some sharp edges. I assume it was a seam weld.

I'm sure it wouldn't matter for fluids or compressed gasses, but it seems like it would wreck havoc on any wires that were pulled into a long run.

I'm assuming the 10' lengths of pipe would have the same thing.
 
steve66 said:
I just recently looked at some black iron and galvanized plumbing pipe nipples, and they have a very noticeable ridge on the inside with some sharp edges. I assume it was a seam weld.

I'm sure it wouldn't matter for fluids or compressed gasses, but it seems like it would wreck havoc on any wires that were pulled into a long run.

I'm assuming the 10' lengths of pipe would have the same thing.
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I think that black pipe is available either welded or seamless. A quick look online suggests that seamless is generally at Schedule 80 or higher, and it does cost more.
 
gadfly56 said:
He said RMC, not RGS. And as far as suitability goes, the black iron pipe is probably fine, if not better, than RMC, aside from any listing issues. It's designed to hold pressure. Not so much the other way around.
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RMC or RGS, whatever.
It is still a code violation to use plumbing pipe.
 
One of our customers used to use plumbing pipe to wire up their machines. Their electricians used to brag about it to me because the pipe and fittings were cheaper. They even did it in classified areas. I gave up trying to tell them why it was a bad idea.
 
Yeah, that's definitely a bad idea, the plumbing pipe has the ragged ridge from being resistance welded and I seem to recall RMC may have a coating on the inside? Not sure about the second part... I generally use EMT or PVC.
 
kastein said:
Yeah, that's definitely a bad idea, the plumbing pipe has the ragged ridge from being resistance welded and I seem to recall RMC may have a coating on the inside? Not sure about the second part... I generally use EMT or PVC.
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Metal conduit (and I think EMT) have a lacquer like substance sprayed on the inside of it for corrosion resistance. There is also a UL spec for how smooth the inside is.

Having said that, I have seen a bunch of places where people used pipe fittings (especially elbows) in lieu of conduit fittings because they are cheaper and take less space. I think it is a minor violation in the grand scheme of things. But a violation none-the-less.
 
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