RNC ambient / LFNC length

[TwistLock]

Coming out the bottom of an exterior surface mount panel with RNC Sch 80, to LB (nm) through raised foundation, use remaining length of Sch 80 under house (exiting LB), then direct transition to about 4ft. of LFNC to come up inside a wall to terminate / connect to a metal box / outlet.
Couple of dumb questions:
I don’t use pvc that much anymore so I’m a little fuzzy on temp ratings… when the mfg says their RNC is rated for use with 90C conductors are they saying the pipe is rated at 90C ambient or just that it’s fine to install 90C conductors as long as I rate the conductors at 75C etc. or whatever not exceeding conduit’s ambient? (I realize the LFNC is only rated for 80C btw). Or is there a calc where you also need to add conductor current temp + conduit ambient? I remember it as you couldn't install RNC where the ambient was in excess of 50°C, but wondered if there were other grades now or new specs (?)

When 356.10 yaps about lengths of LFNC not to exceed 6ft ... am I skirting any intentions by mechanically transitioning from the RNC directly to the short 4ft. piece of LFNC ? I.e. do they just expect LFNC to be only be used as a whip from disco/enclosure etc to equipment?

On an aside - I was reading some of Carlon’s specification lit where they say- “Conduit, fittings & cement shall be produced by the same mfg to assure system integrity.” Makes sense, but is there anything in the code or has anyone had an inspector hold them to this? (just curious, not really important).

 

[Carultch]

If there were a 90C ambient temperature, we'd all be dead. 90F is a realistic ambient temperature, which is approximately 32C.

The 90C rating on conductors refers to the temperature that the insulation can safely withstand, after also accumulating temperature from the conductors, generating ohmic heating. The wiring is tested in a lab with a 30C ambient temperature, and the ampacity is the maximum current that the conductor can carry, while keeping the insulation temperature within a safe margin of the 90C insulation rating rating. There's usually a slight correction you need to make, for typical ambient temperatures in the US, being a little greater than 30C.

Given a 90C rated raceway (e.g. PVC conduit), that means you can take credit for the 90C rating of a conductor, which most is a rating that most conductors made today will have. A metal raceway has no such temperature limitation. For a raceway rated less than 90C, such as 75C or 60C, you can still use 90C rated conductors in it; you just can't take credit for their 90C ampacity as the starting point for your ambient and bundling adjustment calculations. Instead, if you had 90C rated wire in a 75C rated raceway, you'd use the 75C value as the starting point to calculate the ampacity.

It is uncommon that a conduit temperature governs your ampacity. Usually, it is 75C terminations that govern your ampacity (without derate factors), but you are allowed to use the 90C rating where wire derating is applicable.

Flexible raceways, like LFNC and LFMC, are usually only used for a short length. Usually short enough that the 10 ft/10% stub rule can give you an exception, unless it is just a local connection between devices, where you would have to account for its ampacity in this section. This is the advantage of LFMC over its LFNC counterpart, since LFMC usually has a higher temperature rating.

 

[TwistLock]

“It is uncommon that a conduit temperature governs your ampacity.” … this is what had me wondering if I had to ‘further’ derate (on top of breaker/terminal ratings) because the characteristics of PVC do thermally insulate. Thank you for the thorough explanation, much appreciated.

I guess my question about LNFC was if I use it to ‘extend’ a run of other material conduit, but keep the length of the LFNC added extension under 6ft, if I were breaking any rules?

 

[don_resqcapt19]

Coming out the bottom of an exterior surface mount panel with RNC Sch 80, to LB (nm) through raised foundation, use remaining length of Sch 80 under house (exiting LB), then direct transition to about 4ft. of LFNC to come up inside a wall to terminate / connect to a metal box / outlet.
Couple of dumb questions:
I don’t use pvc that much anymore so I’m a little fuzzy on temp ratings… when the mfg says their RNC is rated for use with 90C conductors are they saying the pipe is rated at 90C ambient or just that it’s fine to install 90C conductors as long as I rate the conductors at 75C etc. or whatever not exceeding conduit’s ambient? (I realize the LFNC is only rated for 80C btw). Or is there a calc where you also need to add conductor current temp + conduit ambient? I remember it as you couldn't install RNC where the ambient was in excess of 50°C, but wondered if there were other grades now or new specs (?)

When 356.10 yaps about lengths of LFNC not to exceed 6ft ... am I skirting any intentions by mechanically transitioning from the RNC directly to the short 4ft. piece of LFNC ? I.e. do they just expect LFNC to be only be used as a whip from disco/enclosure etc to equipment?

On an aside - I was reading some of Carlon’s specification lit where they say- “Conduit, fittings & cement shall be produced by the same mfg to assure system integrity.” Makes sense, but is there anything in the code or has anyone had an inspector hold them to this? (just curious, not really important).

That is still the requirement in 352.12(D).

356.10(5) permits lengths longer than 6' where the LFNC is secured in accordance with 356.30.

 

[TwistLock]

That is still the requirement in 352.12(D).

356.10(5) permits lengths longer than 6' where the LFNC is secured in accordance with 356.30.

That’s exactly what I got hung up on. I was reading the Carflex literature where they quote the code and the ‘Uses Not Permitted’ seemed to conflict (in my mind) with the ‘Uses permitted’.
Not Permitted says: “In lengths longer than 1.8 m (6 ft), except as permitted by 356.10(5) or where a longer length is approved as essential for a required degree of flexibility.”
While ‘Uses Permitted’ says hang yourself with it for all we care as long as you strap it, as required in 356.30, we’re good.

My ‘take everything literally’ mind couldn’t parse that they were addressing unstrapped applications and thought that if you wanted to exceed 1.8m (‘strapped’) that you needed an essential reason. (lol, I also thought: “Geez, what’s wrong with this Carflex stuff.”)
I see the problem now - it’s me.