LFMC vs LFNC, how to know when to specify what

[Carultch]

I'd like to get some advice on when to specify LFMC and when (if ever) to not allow LFNC. When I read the "uses permitted" sections in the NEC, they seem like carbon copies of one another. I would expect that LFMC has a better ability to withstand physical damage, but that turns out not to be the case.

So what then is the principle advantage of using the LFMC conduit with the metal core, as opposed to LFNC without?


I know about ground continuity, which could be an advantage or a disadvantage. I'm looking more for environment & location reasons why you would select one over the other.

 

[iwire]

Entirely personal opinion to follow, take it for what it is worth.

I had always used LFMC but decided to start using LFNC for its ease of installation and finding very rusted out LFMC on roofs a number of times.

Well that experiment has ended for me, I found that LFNC was very difficult to get a snake through. I am back to LFMC.

 

[jumper]

I see LFMC speced on most commercial jobs and LFNC on most resi.

All but one defense job specs: LFMC

Why, IDK.

 

[tom baker]

I use a lot of LFNC in industrial applications, where corrosion resistance is needed, such as underground vaults, chlorine rooms, and for instruments. Most of the instruments/analyzers have non metallic enclosures and the LFNC works well with that, and PVC conduit.

I prefer the T&B black LFNC and connectors. IMO, a lot of the LFNC is resi grade.
Later I can post some pictures.
I will use the LFMC in exposed applications where we can't run rigid, for short runs.

For both types, I often see it run unsupported in a sloppy fashion. With some planning it can look very nice

 

[CodeQuandary]

I realize I'm chiming in belatedly, but in case anyone is looking at this in the future (since it popped up in Google with "LFNC vs. LFMC"):
LFNC: per 356.12 (3) can't be longer than 6'
LFMC: per 350, no length limitation.
It seems to me that this is the difference that makes a difference. Obviously, there's more to it, but... this is pretty central.

 

[K8MHZ]

I realize I'm chiming in belatedly, but in case anyone is looking at this in the future (since it popped up in Google with "LFNC vs. LFMC"):
LFNC: per 356.12 (3) can't be longer than 6'
LFMC: per 350, no length limitation.
It seems to me that this is the difference that makes a difference. Obviously, there's more to it, but... this is pretty central.

What about LFNC-B if it's securely fastened every 3 ft. ?

 

[gadfly56]

What about LFNC-B if it's securely fastened every 3 ft. ?

Well now, aren't you the trouble maker?

 

[petersonra]

I've never liked LFMC. The connector seemed to fall apart. I would prefer LFNC personally. LFMC might be a little stronger due to the metal but really if you need the flexibility I don't see why you can't just use plastic altogether instead of plastic coated corrugated metal.

 

[Eddie702]

I agree with @iwire trying to get a snake through LFNC really sucks. I had a 12' run trying to get 3#12s & 2#14s in a 3/4 should have been a snap and it really sucked, not only getting the snake in but pulling the wires by myself was an issue.

I know raceways are supposed to be installed before pulling the wires in but that just makes it more difficult with LFNC

 

[Little Bill]

4 year old thread