75*C vs 90*C

[kwired]

Good question I guess its just a habit that I assume there are few Linear Loads these days.

There are a lot of non linear loads, but that don't automatically mean the majority of the load on a particular feeder or service is non linear, and utilizing the neutral conductor.

Motors and resistance heating add up fast in comparison to electronic ballast/driver type lighting and computers in most places when it comes to total load of the facility.

 

[tortuga]

How does 110.14(C)(1) prevent using adjustment and correction factors?

I am really curious about this also, 110.14(C) was first added in the 1993 code cycle.
It seems if the conductor is operating at 75 C and its listed for a range of conductors that could impose a higher current on it, in theory would not be a problem. I suppose UL ran experiments that demonstrate otherwise.
I found the discussion about it in the
"Report on Comments (ROC) 1993 Technical Committee Documentation (TCD) [Article 90- 230]" on the NFPA website.
The substantiation is:

SUBSTANTIATION: My experience in teaching Code and answering Code questions around the country indicates that the majority of electricians and small electrical contractors, and even some electrical inspectors and design engineers, are unaware of the limitations on conductor ampacity necessitated by the method used in testing of equipment, as indicated in the information published by Underwriters Laboratories Inc. in their various electrical directories. The limitations imposed by proposed new Section 110-14(c) are not new. They are already part of the NEC requirements through Section 110-3(b). The problem is, people who need to know of the limitations do not know of them because they are not in the NEC are are usually not included in the manufacturer's installation instructions. Although there are many other limitations in the use of listed electrical equipment that appear only in the published UL directories, I believe that the limitations on ampacities of conductors because of termination temperature limitations are broad enough and important enough to appear in the Code itself, instead of entering the Code requirements through the back door of Section 110-3(b).

However they did not add the reference to the table till later.
Cheers

 

[jap]

I see (often older) installations all the time that seem to use the "next size up" rule above 800 amps. I use to always think that they must have thought they could always use next size up, but that is a good point - maybe they were (incorrectly) using the 90 degree column for conductor sizing - never thought of that.

I agree, and I'm humble enough to say I've been guilty of doing that also before I knew any better.


JAP>

 

[tortuga]

110.14(C)(1) does not permit you to do that. It specifies the maximum conductor ampacity is the ampacity shown in Table 310.15(B)(16).

Ok I looked into this a little more and the year they added the explicit reference to the table was 2002.
I read the ROP file 70-A2001-ROP.pdf on the NFPA website.
Here is part of the proposal from 2001

SUBSTANTIATION: The objective of this proposal is to clear up
confusion relative to what ampacities are used to determine the
proper conductor size at equipment terminations. When 600V and
less equipment is evaluated relative to the appropriate temperature
characteristics of the terminations, conductors sized based on Table
310-16 are used. The UL General Information Directory (pages 1
and 2) clearly indicates that the 60C and 75C provisions for
equipment have been determined using conductors from Table 310-
16. However, if an installer or designer is not aware of the UL guide
card information, they may attempt to select conductors based on
the Tables other than 310-16. This is especially true if a wiring
method is used that allows the use of ampacities such as those in
310-17. This can result in overheated terminations at the
equipment. Clearly, the ampacities shown in other tables (such as
310-17) could be used for various conditions that the wiring method
is subject to (ambient, ampacity correction, etc.), but the conductor
size at the termination must be based on ampacities from Table 310-
16.
This proposal does not have any new impact on the equipment or
the wiring methods; it simply adds a rule from the listing
information into the Code because it is an installation and
equipment selection issue.

(emphasis added)
The intent appears not to change how wires are sized by eliminating 310.15(B)(2) just to make sure people are not using (then) 310-17
The 500 kCMIL CU wires we were talking about are listed as 380A in 310.15(B)(16) and 620A 310.15(B)(17) thats a huge difference.
Since Table 310.15(B)(16) pulls in 310.15(B)(2) by reference with the note at the bottom it could be argued its part of the table.
Just a thought, Cheers

 

[david luchini]

Ok I looked into this a little more and the year they added the explicit reference to the table was 2002.
I read the ROP file 70-A2001-ROP.pdf on the NFPA website.
Here is part of the proposal from 2001 (emphasis added)
The intent appears not to change how wires are sized by eliminating 310.15(B)(2) just to make sure people are not using (then) 310-17
The 500 kCMIL CU wires we were talking about are listed as 380A in 310.15(B)(16) and 620A 310.15(B)(17) thats a huge difference.
Since Table 310.15(B)(16) pulls in 310.15(B)(2) by reference with the note at the bottom it could be argued its part of the table.
Just a thought, Cheers

I don't see anything to precludes using correction or adjustment factors.

 

[tortuga]

Well I took a quick look at copy of the UL white book
And it appears Don is correct that UL does state they are not using any correction factors.

METER-MOUNTING EQUIPMENT
(PJSR)Unless the equipment is marked to indicate otherwise, the termination provisions are based on the use of 75°C ampacities for wire as specified in Table 310.15(B)(16) of ANSI/NFPA 70, ‘‘National Electrical Code’’ (NEC). However, 3-wire, single-phase service entrance or feeder conductors for dwelling units may be as covered in Section 310.15(B)(7) of the NEC. Termination provisions are determined based on values provided in Table 310.15(B)(16) or Section 310.15(B)(7), with no adjustment made for correction factors.

SWITCHBOARDS (WEIR) SWITCHBOARDS, DEAD-FRONT (WEVZ)
Unless the equipment is marked to indicate otherwise, the termination provisions are based on the use of 60°C ampacities for wire sizes 14 – 1 AWG, and 75°C ampacities for wire sizes 1/0 AWG and larger, as specified in Table 310.15(B)(16) of the NEC. Termination provisions are determined based on values provided in Table 310.15(B)(16), with no adjustment made for correction factors.

 

[david luchini]

Well I took a quick look at copy of the UL white book
And it appears Don is correct that UL does state they are not using any correction factors.

I'm not following...the correction and adjustment factors apply to conductor ampacity. That's not covered by the White Book, unless I am missing it somewhere.

 

[tortuga]

I'm not following...the correction and adjustment factors apply to conductor ampacity. That's not covered by the White Book, unless I am missing it somewhere.

Vlietracer64's plans he bid on show 3 sets of 500 kCMIL CU to a 1200A beraker (or in my case CT lug-set) rated 75C.
I use a correction factor of 1.11 since his conductors are in underground ambient temp of around 18C for 90% of the run.
Included in table 310.15(B)(16) is a reference to 310.15(B)(2) telling us we can correct for the lower ambient temp.
380A * 1.11 = 421.8
421.8 * 3 conductors in the run gives him an ampacity of 1265A
Without the adjustment the rating of the lug falls short of the 1200A breaker at 1140 Amps.
So Don pointed out 110.14(C) which is saying we have to size breakers just based on the table to protect the lugs.
The reasoning is UL did not evaluate any lugs at lower ambient temps with higher current or at other than the ratings in the table 310.15(B)(16). So in Vlietracer64's case 1140 Amp's is the limit for that OCPD size.. If the lugs run at 1265A with my correction factor they might overheat.

 

[david luchini]

Without the adjustment the rating of the lug falls short of the 1200A breaker at 1140 Amps.

We don't know if the lugs fall short, because there hasn't been any discussion of what the lugs are. They will certainly be rated at least 1200A on a 1200A OCPD.

So Don pointed out 110.14(C) which is saying we have to size breakers just based on the table to protect the lugs.
The reasoning is UL did not evaluate any lugs at lower ambient temps with higher current or at other than the ratings in the table 310.15(B)(16). So in Vlietracer64's case 1140 Amp's is the limit for that OCPD size.. If the lugs run at 1265A with my correction factor they might overheat.

If the terminations on the 1200A c/b are rated for, say, (3) 500-700kcmil, and the three 500kcmil conductors have an ampacity of 1265A, then that would be acceptable.

 

[tortuga]

We don't know if the lugs fall short, because there hasn't been any discussion of what the lugs are. They will certainly be rated at least 1200A on a 1200A OCPD.



If the terminations on the 1200A c/b are rated for, say, (3) 500-700kcmil, and the three 500kcmil conductors have an ampacity of 1265A, then that would be acceptable.

Yeah I agree. The lugs are probably #4-600 kCMIL, with a different UL approved amp rating with each wire combination as per the table. The lug would carry 1280 Amps with its maximum size of three 600's. But now I could have those 600's at a lower ambient and run the lug at 1399A, oh wait no I would still be limited to 1200A per 240.
Perhaps the concern is if the wire was adjusted for a lower ambient, while that lower ambient is for 90% of the run its likely not at the lug ( CT can or breaker).

I dont know honestly I think the point of 110.14(C) is they would have only tested the lug at 1000A @ 75C with three 500's.

The theory goes we dont know if the temp can rise above 75C at the termination with the three 500's wire size and since UL states they dont test for that its not allowed. Perhaps Don wants to jump in again and clarify.

 

[oldsparky52]

Is it the lug or the device the lug is attached to? I always thought that most lugs can easily handle 90c connections.

 

[kwired]

Is it the lug or the device the lug is attached to? I always thought that most lugs can easily handle 90c connections.

Most probably can, but the device it is attached to is still usually only rated for 75C.

 

[david luchini]

Yeah I agree. The lugs are probably #4-600 kCMIL, with a different UL approved amp rating with each wire combination as per the table. The lug would carry 1280 Amps with its maximum size of three 600's. But now I could have those 600's at a lower ambient and run the lug at 1399A, oh wait no I would still be limited to 1200A per 240.
Perhaps the concern is if the wire was adjusted for a lower ambient, while that lower ambient is for 90% of the run its likely not at the lug ( CT can or breaker).

It looks like the OP says that the lugs are for (4) 4/0-500kcmil. Four 500kcmil would be 1520A at 75degC.

If the 3 sets of 500kcmil meet the minimum size requirements of 215.2(A) and if the ampacity of the 3 sets of 500kcmil exceeds 1200A after the application of ambient temperature correction factor (so the overcurrent protection meets 240.4(C),) then I don't see any problems with the installation.

 

[jim dungar]

Is it the lug or the device the lug is attached to?

The NEC talks about the temperature rating of the termination not just the lug. The termination consists of the conductor insulation, the conductor, the lug, the lug mounting method, the lug mounting surface, the enclosure, and the ambient temperature near the connection.

 

[tortuga]

It looks like the OP says that the lugs are for (4) 4/0-500kcmil. Four 500kcmil would be 1520A at 75degC.

If the 3 sets of 500kcmil meet the minimum size requirements of 215.2(A) and if the ampacity of the 3 sets of 500kcmil exceeds 1200A after the application of ambient temperature correction factor (so the overcurrent protection meets 240.4(C),) then I don't see any problems with the installation.

Nice attention to detail, so the plans were good.

The NEC talks about the temperature rating of the termination not just the lug. The termination consists of the conductor insulation, the conductor, the lug, the lug mounting method, the lug mounting surface, the enclosure, and the ambient temperature near the connection.

Excellent point, the issue this brings up for me is the NEC should drive the UL standard not UL driving the NEC. IN the UL white book I searched the term Table 310.15(B)(16) and it comes up 47 times and almost always includes the sentance " Termination provisions are determined based on values provided in Table 310.15(B)(16) or Section 310.15(B)(7), with no adjustment made for correction factors. " like under PANELBOARDS (QEUY). I think UL is picking and choosing what parts of the code they test to and instead should test for the entire table 310.15(B)(16) including maximum correction factor of 1.2 @ 75C.

 

[david luchini]

Nice attention to detail, so the plans were good.

The plans in the OPs case would be good if they demonstrated that the ampacity of the conductors is 1200A or greater. I don't see any evidence that that was provided.

 

[don_resqcapt19]

How does 110.14(C)(1) prevent using adjustment and correction factors?

It doesn't unless the correction factor increases the conductor ampacity. It sets the maximum ampacity of any conductor connected to a termination to the ampacity shown in Table 310.15(B)(16)... in other words you can't use smaller conductors or apply a correction factor of greater than 1.

 

[david luchini]

It doesn't unless the correction factor increases the conductor ampacity. It sets the maximum ampacity of any conductor connected to a termination to the ampacity shown in Table 310.15(B)(16)... in other words you can't use smaller conductors or apply a correction factor of greater than 1.

There's nothing in 110.14(C)(1) that prevents applying a correction factor of greater than one, nor is there anything in 110.14(C)(1) that sets a maximum conductor ampacity.

 

[don_resqcapt19]

There's nothing in 110.14(C)(1) that prevents applying a correction factor of greater than one, nor is there anything in 110.14(C)(1) that sets a maximum conductor ampacity.

I don't see how you can read the following any other way. It very clearly sets the maximum ampacity of a conductor connected to a termination the the values shown in Table 31.15(B). It directly references the table values and that eliminates the ampacity correction and adjustment factors from being used where they would increase the ampacity to a value greater than the table value. This is also an issue where conductors that do not have their ampacity set by that table are used.

110.14(C)(1) Equipment Provisions. The determination of termination provisions of equipment shall be based on 110.14(C)(1)(a) or (C)(1)(b). Unless the equipment is listed and marked otherwise, conductor ampacities used in determining equipment termination provisions shall be based on Table 310.15(B)(16) as appropriately modified by 310.15(B)(7).

There is the provision for equipment that is listed and marked for other conductor ampacities and there is a specific permission to use the dwelling unit conductor sizing from 310.15(B)(7), but other than that, we are stuck with the maximum permitted conductor ampacity being that taken directly from the specified table.

 

[david luchini]

I don't see how you can read the following any other way. It very clearly sets the maximum ampacity of a conductor connected to a termination the the values shown in Table 31.15(B). It directly references the table values and that eliminates the ampacity correction and adjustment factors from being used where they would increase the ampacity to a value greater than the table value. This is also an issue where conductors that do not have their ampacity set by that table are used.

There is the provision for equipment that is listed and marked for other conductor ampacities and there is a specific permission to use the dwelling unit conductor sizing from 310.15(B)(7), but other than that, we are stuck with the maximum permitted conductor ampacity being that taken directly from the specified table.

And I don't see how you can read 110.14(C)(1) as limiting the ampacity of a conductor, as it literally says nothing about limiting the ampacity of a conductor. It very clearly talks about "determining equipment termination provisions." Determining equipment termination provisions is not the same thing as determining the ampacity of a conductor. The main section of 110.14(C) provides a limit to the ampacity based on the temperature ratings of the connected terminations, conductors or devices. That would limit the ampacity of the 500kcmil to the 75deg ampacity when it is connected to a 75deg termination, but an ampacity of 422A for a 500kcmil conductor in a 65degF ambient IS the 75deg ampacity.

110.14(C) deals with "Temperature Limitations." The section on Equipment Provisions determines how much current a termination can carry without exceeding the temperature rating of the termination. In the OP, the termination is listed as being for suitable for (4) 4/0-500kcmil conductors. Per 110.14(C)(1), that would make the termination capable of carrying 1520 amps without exceeding the 75 deg rating (4x380A.) If I only connect (4) 350 kcmil conductors, that doesn't change the rating of the termination to 1240A. It is still capable of carrying 1520 amps without exceeding 75deg. In the same way, if I only connect (3) 500kcmil conductors, that doesn't change the rating of the termination to 1140A. The termination is still rated to carry 1520A.

As an example, let's say you had a 1200A feeder you needed to run from a switchboard to a distribution panelboard in a warehouse where the ambient temperature will not exceed 60degF. The breaker in the switchboard has termination provisions for (4) 4/0-500kcmil conductors. The main lugs in the distribution panelboard have termination provisions for (3) 500-700kcmil conductors. The load on the feeder is 1175A non-continuous. The conductors and the termination provisions are rated 75degC. Starting at 215.2(A)(1)(b), I see that three 500kcmil conductors have an ampacity of 1265 after the application of the temperature correction factor. (400kcmil would have an ampacity 1116, so the three 500kcmil would be the smallest allowable conductor.)

Next, 215.3 says that the feeder conductors shall be protected against overcurrent in accordance with Part I of Article 240. 240.4(C) says that the ampacity of the conductors must be equal to or greater than the rating of the OCPD, as the OCPD is over 800 Amperes. We have seen in the previous step that the three 500kcmil conductors has an ampacity of 1265, so they are properly protected by the 1200A c/b.

Now let's go to 110.14(C) for the temperature limitations of the conductors and the termination provisions of the equipment. We have already seen that the conductors can carry 1265 amps without exceeding the 75 deg insulation rating of the conductor. The conductors will only be carry a load of 1175A, so the conductor will be operating at below 75deg. From 110.14(C)(1), I see that the terminations at the breaker can carry (4x380)1520 amps, and the terminations at the breaker can carry (3x460) 1380 amps without exceeding the 75deg rating of the terminations. The terminations at both end will carry a load of 1175A, so the terminations will be operating at well below 75deg.

So in this example, the conductors have sufficient ampacity to carry the load, the conductors are properly protected by the OCPD, the conductors are operating at a temperature below their temperature rating, and the terminations are operating at below their temperature limitiation. That would be a Code compliant installation.