LFMC rated 60C wet location

[Eddie702]

This came up in my MA. code update class I finished yesterday. 2020 code says LFMC is limited to 60C basically. Although you can install 75C or 90c conductors you can only use them at 60c.

I have not found any LFMC rated at 75C wet location. Could be an issue when replacing HVAC equipment and motors especially over 100 amps where conductors are usually sized at 75C

 

[electrofelon]

This came up in my MA. code update class I finished yesterday. 2020 code says LFMC is limited to 60C basically. Although you can install 75C or 90c conductors you can only use them at 60c.

I have not found any LFMC rated at 75C wet location. Could be an issue when replacing HVAC equipment and motors especially over 100 amps where conductors are usually sized at 75C

Interesting. If memory serves correct lfmc has always been marked as such, interesting they put this in the code?

 

[don_resqcapt19]

Interesting. If memory serves correct lfmc has always been marked as such, interesting they put this in the code?

It has been in the code for a long time, but just clarified and relocated in the 2020 code. The 1999 code it was in 351-4(b)(2) which was the uses permitted and said:

(2) Where any combination of ambient and conductor temperature produces an operating temperature in excess of that for which the material is approved

That became 350.12(2) in the 2002 code and was rewritten and moved to 350.10(4) in the 2020 code with 350.12(2) being deleted.

 

[wwhitney]

The text of (2020) NEC 350.10(4) is: "Conductors or cables rated at a temperature higher than the listed temperature rating of LFMC conduit shall be permitted to be installed in LFMC, provided the conductors or cables are not operated at a temperature higher than the listed temperature rating of the LFMC per 110.14(C)."

So for LFMC installed in a wet location and listed only to 60C, does this mean we have to treat all conductors inside as if they had 60C insulation? Both in terms of ampacity before derating, and as far as using the 60C ampacity as the basis for any derating?

Cheers, Wayne

 

[don_resqcapt19]

The text of (2020) NEC 350.10(4) is: "Conductors or cables rated at a temperature higher than the listed temperature rating of LFMC conduit shall be permitted to be installed in LFMC, provided the conductors or cables are not operated at a temperature higher than the listed temperature rating of the LFMC per 110.14(C)."

So for LFMC installed in a wet location and listed only to 60C, does this mean we have to treat all conductors inside as if they had 60C insulation? Both in terms of ampacity before derating, and as far as using the 60C ampacity as the basis for any derating?

Cheers, Wayne

It means that the maximum operating current of the conductors in the LFMC cannot exceed the 60°C ampacity. It has nothing to do with ampacity adjustment or correction...just the actual current through the conductor cannot exceed the 60°C ampacity.

 

[wwhitney]

It means that the maximum operating current of the conductors in the LFMC cannot exceed the 60°C ampacity. It has nothing to do with ampacity adjustment or correction...just the actual current through the conductor cannot exceed the 60°C ampacity.

To be concrete, say you have THWN-2 #8 Cu conductors in LFMC in a wet location with a listing temperature of 60C, and the ambient temperature is 30C. I would say that the language of 350.10(4) means:

If you have (1)-(3) CCCs, then the ampacity is 40A, the 60C base ampacity with no adjustment or correction required.

If you have (4)-(6) CCCs, the ampacity is 32A, the 60C base ampacity with a 0.8 adjustment factor.

Is that what you mean by "60°C ampacity"?

Cheers, Wayne

 

[retirede]

I don’t know if it’s still true, but back in the 80s, we used CSA listed LFMC on our equipment because it was rated 75 while UL and UL/CSA listed was only good for 60.

 

[Eddie702]

The text of (2020) NEC 350.10(4) is: "Conductors or cables rated at a temperature higher than the listed temperature rating of LFMC conduit shall be permitted to be installed in LFMC, provided the conductors or cables are not operated at a temperature higher than the listed temperature rating of the LFMC per 110.14(C)."

So for LFMC installed in a wet location and listed only to 60C, does this mean we have to treat all conductors inside as if they had 60C insulation? Both in terms of ampacity before derating, and as far as using the 60C ampacity as the basis for any derating?

Cheers, Wayne

That is my understanding

 

[Eddie702]

You can find sealtite rated more than 60C. It's all over the place .

The key thing is it's limited to 60C in a WET location........Roof top ac, outdoor chillers and condensing units


Let's say you have a condensing unit with a MOCP of 25 and a minimum circuit amps of 19.

Legally you can use #14 wire @75C but because your in sealtite you would have to use #12

But I am more concerned about the stuff over 100amps that usually gets sized at 75C

In the 2020 Code it's 350.10 (4)

You size your wire at 75C and your ok then you slide it through sealtite and your not.

This only applies to the "operating temp" not the wire rating

 

[Rick 0920]

The text of (2020) NEC 350.10(4) is: "Conductors or cables rated at a temperature higher than the listed temperature rating of LFMC conduit shall be permitted to be installed in LFMC, provided the conductors or cables are not operated at a temperature higher than the listed temperature rating of the LFMC per 110.14(C)."

So for LFMC installed in a wet location and listed only to 60C, does this mean we have to treat all conductors inside as if they had 60C insulation? Both in terms of ampacity before derating, and as far as using the 60C ampacity as the basis for any derating?

Cheers, Wayne

Treat it just as you would NM-B cable.

 

[wwhitney]

Treat it just as you would NM-B cable.

I see it as more restrictive than the 60C limitation on NM-B. In the example I gave, you could derate #8 Cu conductors in NM-B starting at the 90C ampacity, because of the 90C insulation on the conductors. The operating temperature of the NM-B conductors thus may exceed 60C. Whereas in the LFMC the operating temperature is limited to 60C, so any derating must start at the 60C ampacity.

Cheers, Wayne

 

[electrofelon]

This is another one of those things I find annoying and frustrating. First, what is the issue with using LFMC with conductors sized at 75 degrees in a wet location? Have there been any reported problems whatsoever? Can't they make lfmc approved/rated/listed whatever for 75° wet so we just don't even have to worry about another stupid ridiculous technicality? Secondly, it just annoys me that the cmps are investing any resources in such a silly thing when there are far greater problems in the code that need rectifying. /Rant

 

[Rick 0920]

I see it as more restrictive than the 60C limitation on NM-B. In the example I gave, you could derate #8 Cu conductors in NM-B starting at the 90C ampacity, because of the 90C insulation on the conductors. The operating temperature of the NM-B conductors thus may exceed 60C. Whereas in the LFMC the operating temperature is limited to 60C, so any derating must start at the 60C ampacity.

Cheers, Wayne

Unless I'm not understanding 334.80 correctly, I don't see where its operating temperature can be greater than a 60° C. conductor. This section allows you to use the 90° C. rating for adjustment and correction provided the final derated ampacity doesn't exceed that of a 60° C. conductor.

 

[winnie]

The basis of ampacity calculations is that the wire will actually hit the temperature limit used in the calculation.

If you have lots of conductors bundled together then you have mutual heating (or you could say that each conductor experiences a higher ambient because of the others).

So to the extent that the ampacity calculations are correct (we know that in reality they are very conservative) one should expect that when you use the 75C value for derating that the conductors will actually heat up to 75C.

This gives a bit of wiggle room, the code doesn't say 'use the 60C values in your ampacity calculations', it says that the conductors should not exceed 60C. But the ampacity calcs are conservative and conductors almost always run cooler then expected.

On the other hand, if you are derating for ambient conditions this doesn't help much. Sealtight on a 55C roof? You've got a problem.

Jon

 

[wwhitney]

Unless I'm not understanding 334.80 correctly, I don't see where its operating temperature can be greater than a 60° C. conductor. This section allows you to use the 90° C. rating for adjustment and correction provided the final derated ampacity doesn't exceed that of a 60° C. conductor.

On the adjustment and correction computations, you could do those starting either at the 60C rating or the 90C rating.

If you do them starting with the 60C rating, you get a (conservative computational estimate of a) current level that will keep the insulation temperature below 60C, which is the whole point. As soon as you start your computation with the 90C rating, you are saying it's OK if the insulation gets up to 90C, and by getting an answer larger than the 60C answer, you no longer have any guarantee the insulation temperature won't exceed 60C.

Another of looking at is it that 334.80 is effectively saying NM cable shall only be used at 60C termination temperature, the check where you don't do adjustment and correction. While the 60C LFMC wet limit also encompasses the ampacity check along the run of the conductor, where you do do adjustment and correction.

Cheers, Wayne

 

[wwhitney]

Can't they make lfmc approved/rated/listed whatever for 75° wet so we just don't even have to worry about another stupid ridiculous technicality?

A 75C wet rating would be an improvement, but you'd still be limited to starting with the 75C ampacity when doing adjustment and correction. You'd need a 90C wet/dry rating in order to not have to worry about it.

Note that this situation contrasts with PVC conduit, where to my understanding it has a 90C rating. At least, this FAQ says "All CANTEX UL listed conduit and fittings are rated for 90°C (194°F) wiring."

Frequently Asked Questions (FAQ) | Resources | Cantex Inc

Frequently asked questions. We have a list of frequently asked questions and answers. Where can I find information on PVC Conduit? Does the temperature effect PVC conduit installations?...

www.cantexinc.com

Cheers, Wayne

 

[Dennis Alwon]

A 75C wet rating would be an improvement, but you'd still be limited to starting with the 75C ampacity when doing adjustment and correction. You'd need a 90C wet/dry rating in order to not have to worry about it.

Note that this situation contrasts with PVC conduit, where to my understanding it has a 90C rating. At least, this FAQ says "All CANTEX UL listed conduit and fittings are rated for 90°C (194°F) wiring."

Frequently Asked Questions (FAQ) | Resources | Cantex Inc

Frequently asked questions. We have a list of frequently asked questions and answers. Where can I find information on PVC Conduit? Does the temperature effect PVC conduit installations?...

www.cantexinc.com

Cheers, Wayne

Why would the raceway affect the starting point? If the wire is rated 90C then you derate from 90C not 75C or 60C

 

[don_resqcapt19]

To be concrete, say you have THWN-2 #8 Cu conductors in LFMC in a wet location with a listing temperature of 60C, and the ambient temperature is 30C. I would say that the language of 350.10(4) means:

If you have (1)-(3) CCCs, then the ampacity is 40A, the 60C base ampacity with no adjustment or correction required.

If you have (4)-(6) CCCs, the ampacity is 32A, the 60C base ampacity with a 0.8 adjustment factor.

Is that what you mean by "60°C ampacity"?

Cheers, Wayne

I mean the value shown in the 60°C column of Table 310.16.

 

[winnie]

Why would the raceway affect the starting point? If the wire is rated 90C then you derate from 90C not 75C or 60C

The starting point for any ampacity calculation is the temperature that the conductor will get to when used at full ampacity.

If you calculate the ampacity of a 90C conductor in a specific situation to be 24A, then if you run 24A through that conductor you expect it to heat up to 90C. (Note, however that the NEC ampacity calculations are notoriously conservative, and in the real world running that the 'rated ampacity' is unlikely to really heat things up to the rated temperature.)

If you have a conductor running at 90C in a conduit, what temperature is the _conduit_ being exposed to ?

-Jon

 

[Dennis Alwon]

The starting point for any ampacity calculation is the temperature that the conductor will get to when used at full ampacity.

If you calculate the ampacity of a 90C conductor in a specific situation to be 24A, then if you run 24A through that conductor you expect it to heat up to 90C. (Note, however that the NEC ampacity calculations are notoriously conservative, and in the real world running that the 'rated ampacity' is unlikely to really heat things up to the rated temperature.)

If you have a conductor running at 90C in a conduit, what temperature is the _conduit_ being exposed to ?

-Jon

I am talking about starting the de-rate calculation. If you have 90C wire and the conduit is 60C I understand the ampacity cannot exceed the 60C column of the conductor but the de-rate starts at 90C. What am I missing. I thought Wayne was saying you start at 60C or 75C whatever the conduit rating may be.