Liquid Tight Flexible Metalic (LFMC)

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milmat1

milmat1

"It Can't Do That !"
Location
Siler City, NC USA
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Controls Engineer
I keep running into the same argument with different people. Over the use and restrictions involved in using liquid tight metallic flex, (LFMC)

We are an OEM that builds custom machinery for several industries.

I often use liquid tight flex around and on machines. I also will sometimes use this flex to run from a free standing control panel over to the machine, usually into a large J-box or smaller control panel etc that is mounted on the machine.

My question is what are the limitations of using LFMC Liquid tight flex ? I cannot find any limitation on length of flex, unless you are using the conduit as a ground conductor. But as for running it from the panel to the machine, or just general use I can't find anything?

The project that presently brought this question up again is one that will be installed in a wet location. Any additional restrictions there ?

As I said we are an OEM and build an engineered product so we have very few limitations however we do want to stick as close as possible to the NEC as a general rule..
 
Jumper, Thanks for the fast reply,

How about the case where it is run across the floor from the control panel to a machine ?

There's not really a way to secure it and still allow the cabinet to move around some ?
 
milmat1 said:
Jumper, Thanks for the fast reply,

How about the case where it is run across the floor from the control panel to a machine ?

There's not really a way to secure it and still allow the cabinet to move around some ?
Click to expand...

I don't think that would be allowed, depending on what you mean by "move around some".
 
milmat1 said:
Jumper, Thanks for the fast reply,

How about the case where it is run across the floor from the control panel to a machine ?

There's not really a way to secure it and still allow the cabinet to move around some ?
Click to expand...


LFMC and its nonmetal cousin LFNC, are not permitted where "subject to physical damage". And that term is open to interpretation on what it actually means.

If you are running conduit across the floor (not something I would advise in the first place), it probably should be RMC or IMC so the raceway remains intact when someone trips on it. You then can transition to LFMC when connecting to the equipment, as long as you keep the LFMC portion in a place where it is shielded from damage, and of course support it properly.

For minimizing trip hazards, I'd recommend concealing the conduit beneath the finished floor, if at all practical. And then you wouldn't need to concern yourself with it being subject to physical damage. In such a run, I'd probably be using EMT, as it can go a lot farther between supports than flex.
 
If you are using LFMC to connect control cabinets, be sure to pay attention to 250.96 and 314.3. You can't bring metallic raceways into a non metallic enclosure without maintaining continuity.

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The argument can be made that it can't be installed with more than 360 degrees of bends between boxes, as it is conduit.
 
Strathead said:
The argument can be made that it can't be installed with more than 360 degrees of bends between boxes, as it is conduit.
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There is no argument to be made, that is a straight up code fact. :)

From the LFMC code article

350.26 Bends — Number in One Run. There shall not be more than the equivalent of four quarter bends (360 degrees total) between pull points, for example, conduit bodies and boxes.
Click to expand...
 
milmat1 said:
Jumper, Thanks for the fast reply,

How about the case where it is run across the floor from the control panel to a machine ?

There's not really a way to secure it and still allow the cabinet to move around some ?
Click to expand...

Well that sure changes the first question.

If the area of the floor that it is running across is an area one must travel to egress any area, then it can't create a trip hazard, from a life safety and building code perspective. Others have said it can't be subject to physical damage under the NEC. I suggest an overfloor raceway which has sloped sides. I don't know what size you are talking about or what size stock overfloor raceway material comes in.
 
Rules changed

Rules changed

There was a 6 foot limit at one time but that haschanged. The machines we get in thatneed that control station remote are protected by sloped above floor protectors.
 
mgookin said:
Well that sure changes the first question.

If the area of the floor that it is running across is an area one must travel to egress any area, then it can't create a trip hazard, from a life safety and building code perspective. Others have said it can't be subject to physical damage under the NEC. I suggest an overfloor raceway which has sloped sides. I don't know what size you are talking about or what size stock overfloor raceway material comes in.
Click to expand...

Yeah, I guess the question did somewhat evolve, The LFMC is usually less than 10 feet with maybe 6 feet exposed and is most often 1-1/4" flex. I have suggested that on the machines that require this setup we make a steel sloped cover for the flex. We have a structural steel division that makes things like that every day so it should be no problem..
 
iwire said:
There is no argument to be made, that is a straight up code fact. :)

From the LFMC code article
Click to expand...

We often coil five feet of flex behind UPS units so they can be pulled out for maintenance,
Imagine my surprise when that was pointed out to me. I knew it of course, just never thought about it being a violation.
 
milmat1 said:
We are an OEM that builds custom machinery for several industries.
Click to expand...

I would think that removes you from the NEC requirements. As long as your "Machine" has a UL listing, that is that. However, that said the interface between your "Machine" and control panel if not on the same "Skid" would fall under the jurisdiction of the NEC. If movement MUST occur, consider using an energy chain. If walking over the top of the "Umbilical cord" is required, consider a Trenwa trench.
 
Wouldn't mind g be the end users responsibility to keep auxiliary machine interfaces code compliant? I work on industrial machinery every day and when we get new machines we (the buyer and end user) make the necessary arrangements to keep everything compliant, this often involves cutting trenches into the floor or fabbing sloped steel covers


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ADub said:
Wouldn't it be the end users responsibility to keep auxiliary machine interfaces code compliant? I work on industrial machinery every day and when we get new machines we (the buyer and end user) make the necessary arrangements to keep everything compliant, this often involves cutting trenches into the floor or fabbing sloped steel covers


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Click to expand...

Fixed


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