75*C vs 90*C

[kwired]

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.

Right, been mentioned on this site many times before when selecting conductor size you need to basically figure two ampacities, one is based on termination ratings the other based on insulation ratings (which includes any applicable adjustments). If you get two possible sizes the larger conductor is what you must use.

We don't adjust the termination rating, we do make adjustments when insulation is subject to different conditions.

 

[david luchini]

Right, been mentioned on this site many times before when selecting conductor size you need to basically figure two ampacities, one is based on termination ratings the other based on insulation ratings (which includes any applicable adjustments). If you get two possible sizes the larger conductor is what you must use.

We don't adjust the termination rating, we do make adjustments when insulation is subject to different conditions.

So what is the rating of a termination that is suitable for (4) 500kcmil conductors, at 75 deg C?

 

[kwired]

So what is the rating of a termination that is suitable for (4) 500kcmil conductors, at 75 deg C?

From NEC's perspective does that not depend on what size conductors are installed in it? If there are 4 -500kcmil copper then 380 x 4 =1520. If overcurrent protection is 1600 it isn't large enough per 240.4(C).

From listing perspective does it make any sense to make such a 4 port lug that can't handle at least 1520 amps without also creating too much temperature rise? The fact that many lugs alone are listed for 90C means the lug itself can handle even more heat, but the assembly it is a part of may still have a 75C rating, so that makes the lug as well as the conductor landed in it need to be treated as 75C items. We can still use 90C ratings for adjustments in the raceways, cables, etc. so long as we still meet minimum termination ampacity with the final conductor selected.

 

[david luchini]

From NEC's perspective does that not depend on what size conductors are installed in it? If there are 4 -500kcmil copper then 380 x 4 =1520. If overcurrent protection is 1600 it isn't large enough per 240.4(C).

From listing perspective does it make any sense to make such a 4 port lug that can't handle at least 1520 amps without also creating too much temperature rise? The fact that many lugs alone are listed for 90C means the lug itself can handle even more heat, but the assembly it is a part of may still have a 75C rating, so that makes the lug as well as the conductor landed in it need to be treated as 75C items. We can still use 90C ratings for adjustments in the raceways, cables, etc. so long as we still meet minimum termination ampacity with the final conductor selected.

So if the termination rated for 4-500kcmil, 380x4=1520, is installed on a 1200A ocpd, and the load is 1175A on three 500kcmil conductors (with an ampacity of 1265), has the rating or temperature limit of the termination been exceeded?

 

[kwired]

So if the termination rated for 4-500kcmil, 380x4=1520, is installed on a 1200A ocpd, and the load is 1175A on three 500kcmil conductors (with an ampacity of 1265), has the rating or temperature limit of the termination been exceeded?

My thought is probably not, but maybe. How is that for a good solid answer?

 

[david luchini]

How is that for a good solid answer?

That's a fantastic answer...You're covered either way!

 

[jim dungar]

So what is the rating of a termination that is suitable for (4) 500kcmil conductors, at 75 deg C?

What components make up the termination? The quantity of cables only, is not sufficient to provide an answer. The termination will have an rating that is somewhat based on its ability to transfer heat appropriately. Conductors landed on a bus bar style termination pad, made have a different tested rating than the same quantity landed directly on a breaker. For example, a Square D PowerPact PJ frame 800A breaker has available lugs that can handle up to (4) 3/0-500 kcmil where provisions have been included for conductors increased in size for VD reasons.

 

[david luchini]

The quantity of cables only, is not sufficient to provide an answer.

Then what is 110.14(C)(1) saying? The number and size of conductors of the termination, together with the ampacities listed in T310.15(B)(16) tell you how much current can be put through the termination without exceeding the temperature limitation of the termination. Conditions of use will limit how much load current can be put through the termination, but the temperature limit is based on the quantity and size of conductors the termination is designed for.

 

[tortuga]

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.
.

Nice example, take a minute and download the UL whitebook (its free) and search for the term 310.15(B)(16). Almost everywhere its mentioned like the sections 'QEUY' they state

"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. "

UL just does not test termination assemblies for ampacity corrections. Only ones above 1 affect terminations so it would not be that hard. Its a oversight on the part of UL from years past that the code panel mistakenly tried to fix for them. If 110.14(C) were not in the code it would just be a violation of 110.3(B)
110.14(C) was added in the code in 1993 because this concern of the instructor that submitted it:

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...

-- from the proposal
It was not even proposed by UL.

 

[rlqdot]

From NEC's perspective does that not depend on what size conductors are installed in it? If there are 4 -500kcmil copper then 380 x 4 =1520. If overcurrent protection is 1600 it isn't large enough per 240.4(C).

From listing perspective does it make any sense to make such a 4 port lug that can't handle at least 1520 amps without also creating too much temperature rise? The fact that many lugs alone are listed for 90C means the lug itself can handle even more heat, but the assembly it is a part of may still have a 75C rating, so that makes the lug as well as the conductor landed in it need to be treated as 75C items. We can still use 90C ratings for adjustments in the raceways, cables, etc. so long as we still meet minimum termination ampacity with the final conductor selected.

If I understand this correctly, wouldn't the termination ampacity be 4 x 380 only if there are four 500 kcmil wires in the termination - doesn't it depend on the contact area between the lug and the copper conductor to disippate the heat? Code says 380 amps for 500 kcmil wire terminated on 75 degree C lugs because that is the maximum amperage those two surfaces can conduct before overheating the termination.

 

[Carultch]

If I understand this correctly, wouldn't the termination ampacity be 4 x 380 only if there are four 500 kcmil wires in the termination - doesn't it depend on the contact area between the lug and the copper conductor to disippate the heat? Code says 380 amps for 500 kcmil wire terminated on 75 degree C lugs because that is the maximum amperage those two surfaces can conduct before overheating the termination.

The terminal ampacity would be based on the 75C column, regardless of how many wires are terminated in the group. It has to do with the whole equipment (i.e. everything inside the factory-assembled enclosure) being rated for 75C. The default rule for anything over 100A is 75C. 100A and less, the formal rule for the default rating is 60C, but in practice, most equipment is listed and labeled otherwise for 75C. Even if the lugs themselves are marked for 90C, you do not necessarily get to take credit for this. Yes, getting proper lug contact area per the lug manufacturer is also important, but that is an unrelated issue.

It is a less common case for equipment listings to allow use of the 90C ampacity for the terminations. Where you usually see this in practice, is when you start with an initially empty enclosure, and populate it with separately supplied connectors, such as Polaris tap blocks. You might also see this in a case where your enclosure starts as nothing but busbars, and the lugs are separately-installed. You can theoretically use the 90C wire for the majority of the run, as long as you terminate in separate enclosures, with 75C sizing (90C wire) locally at the equipment on both ends. That is a more theoretical example, than one I'd expect to find in practice. The most common reason in practice that you care about the value of 90C wire, is ambient temperature/conductor bundling derate factors, which apply to the wire run and not to the terminations.