3/4" LFMC with different bend radii are sold in the market

[Bill Cowhig]

350.24, references me to Table 2 Chapter 9. There it tells me the minimum bending radius (for LFMC, but the table seems more appropriate for metal conduits) is 5". If the LFMC I buy has a bending radius of, say only 4.25", why does the NEC require me to maintain a minimum bending radius of 5". I'm all for having good rules, but if a rule isn't logical. . .

 

[infinity]

Are you saying that you can purchase LFMC in pre-bent pieces or is this a field bend?

Welcome to the Forum.

 

[Bill Cowhig]

I am saying that I can buy 3/4" LFMC with different "Bend Radii," for example 2.5" 3.5", 4.25", 5", depending on manufacturer's specification, and the NEC permits manually bending the LFMC in the field, without using auxiliary equipment, but then takes away what advantage you might get from having a smaller bend radius by requiring you to bend it to a 5" bending radius.

 

[infinity]

I am saying that I can buy 3/4" LFMC with different "Bend Radii," for example 2.5" 3.5", 4.25", 5", depending on manufacturer's specification, and the NEC permits manually bending the LFMC in the field, without using auxiliary equipment, but then takes away what advantage you might get from having a smaller bend radius by requiring you to bend it to a 5" bending radius.

So you're saying that the stuff is physically manufactured to permit smaller radii bends but the NEC still limits it to 5" for 3/4" due to Chapter 9, Table 2.

 

[Bill Cowhig]

Yes, that’s what I have concluded by a lot of searching.

So I guess I am asking why the manufacturers do that, knowing about the NEC rule for using it, as well as why the NEC would have that rule if the manufacturers can manufacture to smaller bending radii?

 

[don_resqcapt19]

Is it all listed LFMC? The non-listed versions always have a tighter permitted bending radius.

 

[Bill Cowhig]

One of the companies with tighter bend radius had their product certified to three recognizable standards, but not UL

What listing standards are required for this conduit to be used within NEC?

Question: what did you mean by “permitted” in your last sentence?

 

[synchro]

Is it all listed LFMC? The non-listed versions always have a tighter permitted bending radius.

Yes, I notice that the ones with a tighter bending radius are often targeted for use on machinery, and can sometimes be used as part of a listed assembly.
I believe that the NEC rules on bending radius are to limit the sidewall force and resulting friction when pulling wires or cables through them. The bending radius that the manufacturers specify is the minimum value that can be used without potentially damaging them, and is a consequence of their design, construction and, materials. Although it's a relatively small factor, sometimes the bending radius is specified on the inside edge of the LFMC, and sometimes on the center of the LFMC.

Some examples of various types of LFMC are included here:
https://rexel-cdn.com/Products/8DAA...3CC3/8DAAB0BE-E658-468A-B6CA-F0154FDD3CC3.pdf

 

[Bill Cowhig]

Yes, I notice that the ones with a tighter bending radius are often targeted for use on machinery, and can sometimes be used as part of a listed assembly.
I believe that the NEC rules on bending radius are to limit the sidewall force and resulting friction when pulling wires or cables through them. The bending radius that the manufacturers specify is the minimum value that can be used without potentially damaging them, and is a consequence of their design, construction and, materials. Although it's a relatively small factor, sometimes the bending radius is specified on the inside edge of the LFMC, and sometimes on the center of the LFMC.

Some examples of various types of LFMC are included here:
https://rexel-cdn.com/Products/8DAA...3CC3/8DAAB0BE-E658-468A-B6CA-F0154FDD3CC3.pdf

Thank you, synchro, It must be UL listed. One I am thinking about is, and it has a bending radius of 5", No further questions.