Sealtight uses

[frofro19]

Are the conductors in liquid tight limited to the 60° column if outside going to a AC unit? And if outside, would that be considered a wet location? Or could 75° conductors be used in the sealtight?

 

[infinity]

Yes outside is a wet location but the conductors maximum temperature can exceed that of the rating of the raceway. A 90° C conductor can be used even if the raceway limits the ampacity to 60° C.

 

[frofro19]

Yes outside is a wet location but the conductors maximum temperature can exceed that of the rating of the raceway. A 90° C conductor can be used even if the raceway limits the ampacity to 60° C

So I guess my question is, does all sealtight limit the conductors to the 60° C ampacity? In other words, is there any sealtight that allows 75° C conductors if inside? And I assume if outside would require 60°C conductors always even if the sealtight would allow 75° C conductors?

 

[retirede]

So I guess my question is, does all sealtight limit the conductors to the 60° C ampacity? In other words, is there any sealtight that allows 75° C conductors if inside? And I assume if outside would require 60°C conductors always even if the sealtight would allow 75° C conductors?

There is (or at least used to be) CSA only (not UL) sealtite that is rated 75C.

 

[wwhitney]

Yes outside is a wet location but the conductors maximum temperature can exceed that of the rating of the raceway. A 90° C conductor can be used even if the raceway limits the ampacity to 60° C.

But can you use its 90C ampacity rating as the base for ampacity adjustment and correction?

Doing that sort of implies that the conductor insulation might reach 90C, and it certainly seems wrong to have a conductor at 90C in contact with a raceway that is limited to 60C.

And the terminations are in enclosures, not in the sealtite, but can you use the 75C ampacity for terminations?

Cheers, Wayne

 

[frofro19]

And the terminations are in enclosures, not in the sealtite, but can you use the 75C ampacity for terminations?

That's what I was wondering. In some cases you could have THHN rated at 75°C conductors from the panel to a disconnect and have to up size the conductors to meet the 60°C limitations in the sealtight. For instance, an AC unit of MCA of 32 amps could have #10 THHN conductors, rated at 35 amps from the 75°C column from panel to disconnect and require #8 THHN conductors rated at 40 amps from the 60°C column from disconnect to unit if in sealtignt.

 

[infinity]

That's what I was wondering. In some cases you could have THHN rated at 75°C conductors from the panel to a disconnect and have to up size the conductors to meet the 60°C limitations in the sealtight. For instance, an AC unit of MCA of 32 amps could have #10 THHN conductors, rated at 35 amps from the 75°C column from panel to disconnect and require #8 THHN conductors rated at 40 amps from the 60°C column from disconnect to unit if in sealtignt.

Using all of the numbers in your example would that cause the temperature of the conductors to exceed 60° C during the operation of the equipment?

 

[kwired]

Using all of the numbers in your example would that cause the temperature of the conductors to exceed 60° C during the operation of the equipment?

Probably not for the typical AC installation. However NEC sort of thinks it will or they wouldn't have 60, 75 and 90C ampacity tables.

Kind of no different than them requiring NM cable to be used at a 60C rating even though individual conductor insulation is likely same thing as 90C conductors have.

 

[Tulsa Electrician]

Keep in mind thhn can not be used in a wet location.

 

[frofro19]

Keep in mind thhn can not be used in a wet location.

But isn't most THHN wire actually rated as THHN/THWN?

 

[LarryFine]

But isn't most THHN wire actually rated as THHN/THWN?

It is, but you gotta make sure that W rating is in there.

I wonder, is MTW wet-rated, or does the W stand for 'wire'?

 

[rainwater01]

It is, but you gotta make sure that W rating is in there.

I wonder, is MTW wet-rated, or does the W stand for 'wire'?

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


Sent from my iPhone using Tapatalk

 

[don_resqcapt19]

That's what I was wondering. In some cases you could have THHN rated at 75°C conductors from the panel to a disconnect and have to up size the conductors to meet the 60°C limitations in the sealtight. For instance, an AC unit of MCA of 32 amps could have #10 THHN conductors, rated at 35 amps from the 75°C column from panel to disconnect and require #8 THHN conductors rated at 40 amps from the 60°C column from disconnect to unit if in sealtignt.

In my opinion, you do not use the MCA for this purpose...you use the actual compressor running current plus the condenser fan current. The 25% adder required by the NEC is not the current that the unit runs at and that 25% does not add to the temperature of the conductor.

 

[don_resqcapt19]

It is, but you gotta make sure that W rating is in there.

I wonder, is MTW wet-rated, or does the W stand for 'wire'?

MTW = Machine-tool Wire, however is it a wet location wire at 60°. Also the use is limited to within machine tools by Table 310.4 (310.104 in older codes) unless it is a dual rated product

 

[infinity]

In my opinion, you do not use the MCA for this purpose...you use the actual compressor running current plus the condenser fan current. The 25% adder required by the NEC is not the current that the unit runs at and that 25% does not add to the temperature of the conductor.

I agree, but if you say that the raceway can only be used up to the 60° C conductor ampacity then in frofro's example the #10 is too small.

 

[Eddie702]

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

 

[retirede]

MTW is hard to pull. If you have to pull any distance, you’re punishing yourself!

 

[don_resqcapt19]

I agree, but if you say that the raceway can only be used up to the 60° C conductor ampacity then in frofro's example the #10 is too small.

But the code language in 350.10(4) says
"... provided the conductors or cables are not operated at a temperature higher than the listed temperature rating of the LFMC"
The conductors are operated at the temperature that the actual current draw creates.

 

[infinity]

But the code language in 350.10(4) says
"... provided the conductors or cables are not operated at a temperature higher than the listed temperature rating of the LFMC"
The conductors are operated at the temperature that the actual current draw creates.

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.

 

[wwhitney]

But the code language in 350.10(4) says
"... provided the conductors or cables are not operated at a temperature higher than the listed temperature rating of the LFMC"
The conductors are operated at the temperature that the actual current draw creates.

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