Sealtight uses

[don_resqcapt19]

Correct. So when sizing the conductors you would need to ensure that they do not operate above 60° C when using the flex in a wet location. You would not use the 60° conductor ampacity to size the conductors.

I would use a conductor that has a 60°C ampacity equal to or greater than the actual running current.

 

[infinity]

I think that 350.12(2) is unique because the raceway has a 60° C limitation when used in a wet location. This wouldn't apply to metallic raceways so Don's method of calculation seems to meet the intent of (2).

350.12 Uses Not Permitted. LFMC shall not be used as follows:
(1) Where subject to physical damage
(2) Where any combination of ambient and conductor temperature produces an operating temperature in excess of that for which the material is approved

 

[don_resqcapt19]

The question is what procedure is allowed by the NEC to determine the operating temperature?

Certainly sizing conductors based on their 60C ampacity should ensure that the operating temperature is below 60C, but perhaps that is overly conservative.

So if you have a circuit that calculates out under Article 220 to be 45 amps (non-continuous), but which you instrument under all operating and ambient conditions (which do not exceed 30C) and find never exceeds 38A, are you saying that 75C #8 Cu conductors on a 50A circuit would comply with 350.10(4)?

I'm having trouble seeing how the wording in 350.10(4) permits an analysis process not used anywhere else in the NEC, rather than implicitly requiring the use of the Article 220 load.

Cheers, Wayne

I am simply saying that for AC equipment, you use the actual running current as marked on the nameplate and not the MCA for the purposes of determining if the conductor will be operating at a temperature greater than 60°.

 

[kwired]

Don't believe you can use MTW in place of building wire it's restricted to machines etc unless dual rated along with THHN/THWN

FWIW table 310.104(A) does have an entry for MTW, but does mention machine tool wiring in the application provisions as well as has an informational note telling us to see NFPA 79.

 

[kwired]

I am simply saying that for AC equipment, you use the actual running current as marked on the nameplate and not the MCA for the purposes of determining if the conductor will be operating at a temperature greater than 60°.

As you also would for ampacity adjustments for more than three current carrying conductors.

MCA has more to do with minimum conductor allowed regardless of other factors, in some cases adjustments could calculate a smaller conductor but you must still go with whatever MCA is (at the terminal temp rating) as the minimum in those instances.

 

[wwhitney]

I am simply saying that for AC equipment, you use the actual running current as marked on the nameplate and not the MCA for the purposes of determining if the conductor will be operating at a temperature greater than 60°.

I'm open to that idea, although it raises the question: if "nameplate current <= 60C ampacity" is sufficient to say that the conductor won't be operating above 60C, then why is MCA larger than nameplate current?

Seems like it would be that either MCA has to cover a range of conditions wider than you are suggesting that the word "operating" in 350.104(4) covers (e.g. overloads), or MCA is designed to include an extra safety margin that you are suggesting is not required for the LFMC under the wording in 350.104(4).

Cheers, Wayne

 

[wwhitney]

Also, (2020) 350.104(4) references 110.14(C), which says (2017) [2020 doesn't permit cut and paste]:

(C) Temperature Limitations. The temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination, conductor, or device. Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both.

Which I think muddies the waters a bit, but would seem to mean that 110.14(C) should be applied to the LFMC as if "conduit" were included in "temperature rating of any connected termination, conductor, or device."

Cheers, Wayne

 

[tom baker]

Well, according to this it’s 60 degrees when wet.


Sent from my iPhone using Tapatalk

Isn’t it machine tool wire?

 

[James L]

I am simply saying that for AC equipment, you use the actual running current as marked on the nameplate and not the MCA for the purposes of determining if the conductor will be operating at a temperature greater than 60°.

You also need to take ambient temperature into consideration.

Outside temperatures might be as high as 105°
That would require an adjustment of almost 30%

In that kind of ambient temperature, a real world operating temperature limited to 60 degrees would require a #8 to be adjusted down to 28 amps

 

[kwired]

You also need to take ambient temperature into consideration.

Outside temperatures might be as high as 105°
That would require an adjustment of almost 30%

In that kind of ambient temperature, a real world operating temperature limited to 60 degrees would require a #8 to be adjusted down to 28 amps

?? adjustment factor at 105F is .87. that would give a 60C 8 AWG an adjusted ampacity of 34.8 amps.

Then remember the MCA marked on a AC unit already has 125% of the compressor load factored into it.

If MCA was actually 40 and you had 75C terminals you would need 40 amp @ 75 C conductor as minimum size before any adjustments that may apply - those further adjustments apply to insulation temp rating not ther terminations. If further adjustments for insulation result in less size conductor allowed you still need to use the larger conductor required by termination temp rating.

add: 114F ambient would give you a .71 adjustment factor, maybe you got on wrong row when reading table?

 

[infinity]

You also need to take ambient temperature into consideration.

Outside temperatures might be as high as 105°

Is that how you adjust for ambient using the peak temperature?

 

[James L]

add: 114F ambient would give you a .71 adjustment factor, maybe you got on wrong row when reading table?

Are you sure you're in the right line?
105-113f requires .71 adjustment.

And I was commenting toward "real world" temperatures, not something in a derating calculation

 

[James L]

Is that how you adjust for ambient using the peak temperature?

I would look at what's realistic.
If there's a real potential to run "continuous" in that temperature range, then it needs to be wired for such, imho.

Everything we do needs temperature consideration

 

[kwired]

Are you sure you're in the right line?
105-113f requires .71 adjustment.

And I was commenting toward "real world" temperatures, not something in a derating calculation

looks like .87 adjustment to me for 105F and .71 for 114F in the 60C column.

 

[James L]

View attachment 2558810
looks like .87 adjustment to me for 105F and .71 for 114F in the 60C column.

What book/chart are you using?
2017 here

 

[don_resqcapt19]

I'm open to that idea, although it raises the question: if "nameplate current <= 60C ampacity" is sufficient to say that the conductor won't be operating above 60C, then why is MCA larger than nameplate current?

Seems like it would be that either MCA has to cover a range of conditions wider than you are suggesting that the word "operating" in 350.104(4) covers (e.g. overloads), or MCA is designed to include an extra safety margin that you are suggesting is not required for the LFMC under the wording in 350.104(4).

Cheers, Wayne

I have never seen any technical substantiation for the continuous and other loads that require the conductor ampacity to be 125% of the load.

 

[don_resqcapt19]

Are you sure you're in the right line?
105-113f requires .71 adjustment.

And I was commenting toward "real world" temperatures, not something in a derating calculation

Yes, that is the adjustment if the conductor you are using is a 60°C conductor. I have not seen a 60°C conductor installed in a very long time. Almost everything we install is 90° and that adjustment is 0.87.

 

[kwired]

What book/chart are you using?
2017 here
View attachment 2558811

I see now that I was using the table on next page which is for a base ambient of 40C instead of 30C, my bad.