The AM Forum

My question is about the rigid 'knurled' type of metal conduit. It has the inside completely covered in tiny bumps/knobs called "knurls". There's a few hundred ft. of conduit here, put in when the shop was built and the emergency generator installed.

I didn't even know Knurled conduit existed until browsing the pages of the 1949 Westinghouse Electrical Apparatus and Supplies catalog. It's called "Republic brand Inch-Mark Electrunite E.M.T." and was distributed by Westinghouse. (I hope to scan this 900 page book)

A search revealed that the tubing is still made by Nucor to this day and is apparently the same 'Republic Inch-mark Electrunite' type:
https://www.nucortubular.com/product/intermediate-metal-conduit-imc/

Its advantage is claimed to be the easiest to pull wire through, since the wire slides with less friction along the tips of the 'knurls' instead of in flat contact with the whole inside of regular conduit.

I'm wondering why I've never seen it or heard of it today. Is it  more costly or normally reserved for certain situations?

I've never seen it.  At least anywhere it was pointed out.

From the page you posted I dont see anything about knurls inside.  That's a datasheet for standard IMC.

I'd also posit the manufacturer is kind of out there.  They speak of the conduit being the dame size as RMC but having more room for wires inside.

That's not how it works.  Nor does that matter with the last few revisions of NEC, its about current carrying conductor count more than physical space as long as you dont fill the conduit past it's rating.

IE, you can run 4 inch conduit, but you still aren't going to run more than 3 x number 12 current carrying conductors in it!

From thr mfg

After forming and welding, the tubes receive a satin-smooth, corrosion-resistant zinc coating courtesy of Nucor Tubular Product?s exclusive Electrogalvanizing process. A secondary treatment following the zinc coating extends the corrosion-resistance of Nucor Tubular Product?s IMC.

Typical IMC or thin walled rigid.

--Shane
WP2ASS / ex KD6VXI

I guess the only thing I can see that makes it an easy pull is you have less surface area to create friction. But to be brutally honest, I had more problems pulling wires/cables through Sealtite/Flex than I did with EMT or EX pipe.

Satan invented Sealtite 90s.

Prove me wrong.

KD6VXI said:
No argument here!

The knurling is only mentioned here (image) on that page.  Well I suppose it's for some very special applications.