What's the purpose of FMC?

[Mgarf33]

Forgive my ignorance.
So, the NEC states that it cannot be used where the potential for damage exists. Does this not put it in the same category as NMB or UF? So, why bother with the flexible conduit at all?

The only use I can think of, is for using wire having higher ampacity tables of 75° & 90°.
I understand NMB can be used in 90° locations but is limited to 60° ampacity.

 

[infinity]

You're referring to Flexible Metallic Conduit (FMC) Article 348?

 

[Smart $]

...So, the NEC states that it cannot be used where the potential for damage exists...

It actually states not permitted where subject to physical damage. Sort of have to take that with a grain of salt as the potential for physical damage exists everywhere. It is intended to mean: likely to be physically damaged. There are a great many locations where FMC would likely not be physically damaged.

 

[kwired]

Subject to damage is a variable thing. Same circumstances the FMC maybe more damage resistant then a NM cable, less damage resistant then non flexible raceways.

Even RMC is subject to damage in some circumstances but will take more abuse then pretty much any other wiring method.

 

[jaggedben]

Let's see...

Unlike cable you can piece it together without pulling the entire length from point A to B. That can be handy compared to working with larger size cables.

It's also very handy for making short (or longer) transitions between spaces where you'd otherwise be using EMT. Common for us solar guys. Run EMT from inverter in garage through ceiling into attic. Run FMC through attic to a spot where you stub EMT through the roof. Continue with EMT to solar array. Then pull wire all the way without having to make up two j-boxes in the attic as you would if you were running NM there.

Same sort of thing if you're running through a double layered wall or floor with some space in between that makes it hard to perfectly line up EMT.

 

[junkhound]

Forgive my ignorance.
So, the NEC states that it cannot be used where the potential for damage exists. Does this not put it in the same category as NMB or UF? So, why bother with the flexible conduit at all?

The only use I can think of, is for using wire having higher ampacity tables of 75° & 90°.
I understand NMB can be used in 90° locations but is limited to 60° ampacity.

areas with
mice, rats, squirrels, skunks, possums, etc...

 

[jeremysterling]

I like to use FMC in lieu of MC when I fish concealed spaces and need wire colors and sizes that are not standard MC offerings. As an additional advantage, I can pull stranded. I will also have less EGC's to mess with.

 

[al hildenbrand]

So, why bother with the flexible conduit at all?

The only use I can think of, is for using wire having higher ampacity tables of 75° & 90°.
I understand NMB can be used in 90° locations but is limited to 60° ampacity.

That's thinking in the right direction. Many slide-in ovens come from the factory with an FMC whip and conductors that can be of even higher temperature ratings. One can hard wire any range with an FMC whip in the field.

In my work area, Minneapolis / St. Paul, whole subdivisions went in wired almost exclusively with FMC.

Being a raceway, it can have the wires within changed after the conduit is enclosed in the walls. I like to suggest to my clients that have homes wired with FMC that, being a raceway, it is a "Cadillac" wiring method compaired to cable.

 

[jaggedben]

I like to use FMC in lieu of MC when I fish concealed spaces and need wire colors and sizes that are not standard MC offerings. ...

Yeah, that's another good point. When running DC (for solar or otherwise) you don't need a white. Sometimes you have 2-4 reds and blacks each and one green.

Really anything where you are running multiple circuits from the same point A to point B doesn't call for individual cables so much.

 

[growler]

So, why bother with the flexible conduit at all.

You really need flexible conduit when hooking up motors and tranformers or any other equipment with lots of vibration. The flex absorbs the vibration.

You can fish in walls if needed.

 

[gadfly56]

Clean Agent Systems

Clean Agent Systems

It's a life saver for fire suppression system installs. NFPA 2001 requires all initiating device and solenoid circuits to be in "raceway". MC and AC need not apply. It might not make that much difference in new construction vs EMT, but for renovation work it's the only way to go.

 

[lordofthisworld]

Forgive my ignorance.
So, the NEC states that it cannot be used where the potential for damage exists. Does this not put it in the same category as NMB or UF? So, why bother with the flexible conduit at all?

The only use I can think of, is for using wire having higher ampacity tables of 75° & 90°.
I understand NMB can be used in 90° locations but is limited to 60° ampacity.

It’s good for Absorbing a lot of vibration, especially transformers and control cabinets.