Type LFNC 356.12

[mwm1752]

There are no other conduits/tubing that contain the statement " any combination of ambient and conductor temperatures is in excess " I can find in my search. I have a few thoughts on what this means but I'd appreciate specific input for final analysis. Here are my thoughts toward what "combination refers to"

(1) The LFNC will have markings that refer to ambient temperature rating of the conduit.
(2) All conductors are subject to adjustment per NEC article 310.
(3) The size of the conductor will determine the conduit size.
(4) Ambient temperature is determined by yearly average?, Highest possible at any moment? or Highest possibel for a continuous time period? to start the conductor adjustment.(please endorse just one for specifics)

So in a nut shell the combination refers to the conduit temperature rating is appropriate with the surrounding conditions and the sizing of conduit due to conductor circular mils.

ARTICLE 356 Liquidtight Flexible Nonmetallic Conduit: Type LFNC
356.12 Uses Not Permitted
LFNC shall not be used as follows:
(2) Where any combination of ambient and conductor temperatures is in excess of that for which the LFNC is approved

 

[mwm1752]

Lots of views but no comments yet. I did go to the carlon site & talk to a technician. The web site Q&A statement is such:
What temperature limitations apply to Carflex The heat from ambient temperature (surrounding air) plus that from the ampacity
(current) from the conductors may not exceed 80?C (176?F) dry or 60?C (140?F)
wet. This same restriction applies to metal Liquidtight Conduit.
Carflex does not have a lower temperature limitation since it may not be used in
areas where subject to physical damage. PVC material does not breakdown due
to lower temperatures, but will become more brittle and therefore more
susceptible to damage due to physical contact.

The technician comments included the ambient temperature as bieng an average of the warmest 3 months of a year or a conditioned space with possible excessive temperatures. If the conductors are properly size to handle a continuous load the heat from the conductors is a non factor. This does also applies to LFMC.

 

[shortcircuit2]

Bump...

mwm1752...7 years later...how do you apply this rule now?

 

[mwm1752]

2020 NEC made an addition to the section: which would solve the question.
356.10 Uses Permitted.
(8) Conductors or cables rated at a temperature rating of LFNC conduit shall be permitted to be installed in LFNC, provided the conductors or cables are not operated at a temperature higher than the listed temperature rating of the LFNC.
Informational Note: Extreme cold can cause some types of nonmetallic conduits to become brittle and therefore more susceptible to damage from physical contact.

Rating use of conductors is limited to the max rating of the raceway.

 

[kwired]

2020 NEC made an addition to the section: which would solve the question.
356.10 Uses Permitted.
(8) Conductors or cables rated at a temperature rating of LFNC conduit shall be permitted to be installed in LFNC, provided the conductors or cables are not operated at a temperature higher than the listed temperature rating of the LFNC.
Informational Note: Extreme cold can cause some types of nonmetallic conduits to become brittle and therefore more susceptible to damage from physical contact.

Rating use of conductors is limited to the max rating of the raceway.

Someone revived an old thread.

That said seems not exceeding raceway temp rating should be something covered back in 110 to me, or at least in 300 and not in an individual raceway article. There are other non metallic raceways with max temp ratings.

 

[mwm1752]

Not sure how to interprete/calaculate the ampacity (current) from the conductors as a temperature measurement. Thought the Guru's here would have comment. IE: max average ambient temp = 80F then the conductors would be limited 60F on LFNC rated @ 140F?

 

[kwired]

Not sure how to interprete/calaculate the ampacity (current) from the conductors as a temperature measurement. Thought the Guru's here would have comment. IE: max average ambient temp = 80F then the conductors would be limited 60F on LFNC rated @ 140F?

You are mixing deg F and deg C together there. 60C = 140F and would be just fine to use in to use in 80F ambient.

 

[shortcircuit2]

You are mixing deg F and deg C together there. 60C = 140F and would be just fine to use in to use in 80F ambient.

He is not mixing anything. He is saying if it is 80F ambient, then you are limited to 60F conductor temperature (Joule Heating)...to not exceed the 140F LFNC raceway limit (60C) according to 356.12(2) with regard to the UL listing

This language limit also was in 350 for LFMC for a few cycles also.

I have never seen LFNC damage in the field with regard to using ambient and conductor temperature. Has anybody? I believe we are safe to to exercise not exceeding conductor temperature (60C) with LFNC or LFMC in wet location. How? By not loading a conductor beyond the 60C degree column in table 310.16...formerly 310.15(B)(16) (formerly 310.16)

 

[kwired]

He is not mixing anything. He is saying if it is 80F ambient, then you are limited to 60F conductor temperature (Joule Heating)...to not exceed the 140F LFNC raceway limit (60C) according to 356.12(2) with regard to the UL listing

This language limit also was in 350 for LFMC for a few cycles also.

I have never seen LFNC damage in the field with regard to using ambient and conductor temperature. Has anybody? I believe we are safe to to exercise not exceeding conductor temperature (60C) with LFNC or LFMC in wet location. How? By not loading a conductor beyond the 60C degree column in table 310.16...formerly 310.15(B)(16) (formerly 310.16)

I think if there were a 60F conductor it would have very limited number of places it could even be used, guessing he meant 60C conductor which is also 140F and well above his 80F ambient.

 

[mwm1752]

Short Circuit has my comment interpreted correct - 60 C = 140 F -- ambient temperature is 80 F per highest 3 months leaving the temperature rating of the conductor not to exceed 60 F or 15 C in regards to conductor amperage -- note there is no conductors rated @ 15 C but you could derate the conductor amperage values to 15 C causing all sorts of UL issues.

 

[kwired]

I think what you are saying is you can still use 75 or 90C conductor, but you need to use it at 60C ampacity because the raceway is only rated 60C. I did realize that. I think you must have initially said 60F when you meant 60C and that threw me off on what you were trying to say.

 

[mwm1752]

I think what you are saying is you can still use 75 or 90C conductor, but you need to use it at 60C ampacity because the raceway is only rated 60C. I did realize that. I think you must have initially said 60F when you meant 60C and that threw me off on what you were trying to say.

Again what does this statement means?
Where any combination of ambient and conductor temperatures is in excess of that for which the LFNC is approved -

ambient plus conductor temperatures < temperatures for which the LFNC is approved ?
ambient or conductor temperatures < temperatures for which the LFNC is approved ?

Like I stated earlier I think 2020 addressed this with 350.10(4) & eliminating 350.12(2) but no one on this site took a stab at it when I originally posted it.

 

[retirede]

Again what does this statement means?
Where any combination of ambient and conductor temperatures is in excess of that for which the LFNC is approved -

ambient plus conductor temperatures < temperatures for which the LFNC is approved ?
ambient or conductor temperatures < temperatures for which the LFNC is approved ?

Like I stated earlier I think 2020 addressed this with 350.10(4) & eliminating 350.12(2) but no one on this site took a stab at it when I originally posted it.

It means you take the maximum expected ambient, add to that the conductor temperature (per the installation, not the insulation rating) and that sum cannot exceed the rating of the LFNC.

So if the max ambient is 50C and the circuit was sized using 60C ampacity, the raceway must be rated at least 110C.

The fact that the conductors happen to have 90C insulation is irrelevant.

 

[kwired]

Again what does this statement means?
Where any combination of ambient and conductor temperatures is in excess of that for which the LFNC is approved -

ambient plus conductor temperatures < temperatures for which the LFNC is approved ?
ambient or conductor temperatures < temperatures for which the LFNC is approved ?

Like I stated earlier I think 2020 addressed this with 350.10(4) & eliminating 350.12(2) but no one on this site took a stab at it when I originally posted it.

I haven't looked into this too hard, but I don't think you find many LFNC with a rating below 60C. That to me means at very least you select conductors based on 60C ampacity tables regardless if they are actually rated 75 or 90C. Also probably means no adjustments starting with 75 or 90C ampacities

If a LFNC would have an ambient rating of say 80C, you'd probably be safe designing everything around 75C ampacity table, but could design to 80C, though it would be a little more complicated than typical 60, 75 or 90 that we have tables for.

 

[mwm1752]

It means you take the maximum expected ambient, add to that the conductor temperature (per the installation, not the insulation rating) and that sum cannot exceed the rating of the LFNC.

So if the max ambient is 50C and the circuit was sized using 60C ampacity, the raceway must be rated at least 110C.

The fact that the conductors happen to have 90C insulation is irrelevant.

Which made that not permitted code a joke & good riddance to it- most common LFNC rating is 60C - 27C is a low max ambient + 60C conductor ampacity limit is pretty much a non compliant installation in most installations.

 

[EngineerPlayinElectrician]

It means you take the maximum expected ambient, add to that the conductor temperature (per the installation, not the insulation rating) and that sum cannot exceed the rating of the LFNC.

So if the max ambient is 50C and the circuit was sized using 60C ampacity, the raceway must be rated at least 110C.

The fact that the conductors happen to have 90C insulation is irrelevant.

Celsius (and Fahrenheit) temperatures do not add like that. If they did, I would be interested in knowing what is half as cold as -12C. It is not -6C.

Kelvin (and Rankine) scales are "absolute" scales where 0 is the coldest temperature possible (and they do not have negative numbers). They can be added, etc.

There is a good chart comparison here: https://en.wikipedia.org/wiki/Rankine_scale

 

[EngineerPlayinElectrician]

50C plus 60C is 383.15C. :-O

 

[Little Bill]

Start a new thread, this one is 8 years old!