yet more 110.14(C)

[hardworkingstiff]

Looking for more information and understanding I came across this question that was never answered, so I thought I would post it here.

Davidbeach,

Is there a document put out by NFPA or UL that states that even with an oversized mechanical lug, the ability to carry heat away from the termination is still based on the #4/0 conductor?

Wareagle,

The mechanical lugs have a range of "#4/0 to 500kcmil". They are Burndy catalog #KA34. Our #4/0 cable does not physically fit inside of a #KA28. It seems to me that if the #4/0 cable terminated to a #KA34, and the set-screw in the lug is torqued properly, that we would be able to use the ampacity of 500kcmil per table 310.16 for the termination (but not for the conductor). This is because the lug is big enough to carry 500kcmil worth of current and not exceed 75C. Right? Wrong? What are your thoughts? Is there any official documentation to back a right or wrong response?

I tend to think this is a good question and would love to hear the correct answer.

 

[Pierre C Belarge]

Go to google and type in conductor as heat sink...SQD has some good papers on their site about this, so do others.

 

[nakulak]

I am missing something. what difference would it make ?

 

[hardworkingstiff]

Thanks Pierre, didn't see anything but will continue to look.

I've talked to the SQ D breaker application engineer about this and he's sent me information. I understand the concept of going from building wire to the W cable I use to meet the termination restrictions.

What I don't understand is if a termination point is rated at a higher ampacity than is being used (ie a 250-amp rated busbar being fed with a 100-amp circuit) then how does that affect 110.14(C)?

If the lug being used to terminate the conductor is rated at a higher temperature and ampacity than the circuit, how does that affect 110.14(C)?

Like the question posted in the OP, using how does using lower ampacities than the rating of the termination point affect the termination.

 

[hardworkingstiff]

I am missing something. what difference would it make ?

A marine power center I use has a busbar rated 250-amps. A #4 type W cable used on a 120/240-volt circuit has an allowable ampacity of 115A at 75C per table 400.5(B).

110.14(C) limits terminations to ampacities of 310.16.

The cable can handle 115A at 75C.

The termination busbar can handle 250-amps at 75C.

The lug used with the W cable actually can accept a #2 THWN conductor so why can't we use 310.16 ampacity for a #2 since that's the lug rating and we don't approach the limits of any of the other parameters of the connection?

I hope this makes sense (the question that is).

Edit: The lug is rated 150C

 

[nakulak]

thanks, now I understand the question

 

[hardworkingstiff]

Fyi

Fyi

I guess y'all think I'm beating this thing to death, and if it's offensive, sorry.

It's hard for me to accept we have been unsafe for years since we don't have any records of failures.

Eaton owns Marina Power and Light which routinely puts out drawings loading #1/0 and #2/0 type W cable to 200-amps which is a violation of 110.14(C). I've brought this to their attention and they have blown me off.

I'm just trying to get a handle on why 110.14(C) was written and if there is any way to accomadate the methodolgy that has been used at marinas for over decade without problems.

 

[rbalex]

First let’s deal with the two questions cited in the OP.

Davidbeach,

Is there a document put out by NFPA or UL that states that even with an oversized mechanical lug, the ability to carry heat away from the termination is still based on the #4/0 conductor?

Yes, UL has such a document and its free. (Download the “2009 White Book.”)

UL Category Code AALZ, is the general category that applies to all UL listed electrical equipment and was the original basis and source for 110.14(C) in the 1993 Code. Category Code AALZ has prescriptive termination temperature requirements for Appliance, Utilization, Distribution and Control Equipment. In absence of specific permission to do otherwise in a particular product category, this essentially forecloses any other ampacity/temperature rating options.

Wareagle,

The mechanical lugs have a range of "#4/0 to 500kcmil". They are Burndy catalog #KA34. Our #4/0 cable does not physically fit inside of a #KA28. It seems to me that if the #4/0 cable terminated to a #KA34, and the set-screw in the lug is torqued properly, that we would be able to use the ampacity of 500kcmil per table 310.16 for the termination (but not for the conductor). This is because the lug is big enough to carry 500kcmil worth of current and not exceed 75C. Right? Wrong? What are your thoughts? Is there any official documentation to back a right or wrong response?

Wrong. The ultimate limitation in this case is determined by the termination's temperature, not ampacity; i.e., the termination would still run at a higher temperature if a smaller conductor were used with the same current. It is important to remember that, in these cases, the terminations don’t have ampacity ratings and only have temperature ratings based on using proper conductors at their proper ampacity. (For the “official documentation” see question above.)

Now, for the rest of your question. (I hope)

While, I believe most folks understand the underlying physics when explained, I also believe 110.14(C) is poorly worded since it is trying to cover all the relevant content of the White Book as well as incorporate motor and pressure connector requirements. (Motors aren’t listed and pressure connectors DO have ampacity ratings as well as temperature ratings)

From the 2009 White Book, Category Code AALZ:

...
Appliance and Utilization Equipment Terminations
…
Except as noted in the general Guide Information for some product categories, the termination provisions are based on the use of 60?C insulated conductors in circuits rated 100 A or less, and the use of 75?C insulated conductors in higher rated circuits as specified in Table 310.16 of the NEC. If the termination provisions on equipment are based on the use of other conductors, the equipment is either marked with both the size and temperature rating of the conductors to be used or with only the temperature rating of the conductors to be used. If the equipment is only marked for use with conductors having a higher (75 or 90?C) temperature rating (wire size not specified), the 60?C ampacities (for circuits rated 100 A or less) and 75?C ampacities (for circuits rated over 100 A) should be used to determine wire size. Conductors having a temperature rating higher than specified may be used, though not required, if the size of the conductors is determined on the basis of the 60?C ampacity (circuits rated 100 A or less) or 75?C ampacity (circuits rated over 100 A).

Distribution and Control Equipment Terminations
…
Except as noted in the following paragraphs or in the general Guide Information for some product categories, the termination provisions are based on the use of 60?C ampacities for wire size Nos. 14-1 AWG, and 75?C ampacities for wire size Nos. 1/0 AWG and larger, as specified in Table 310.16 of the NEC.

Some distribution and control equipment is marked to indicate the required temperature rating of each field-installed conductor. If the equipment, normally intended for connection by wire sizes within the range 14-1 AWG, is marked ‘‘75C’’ or ‘‘60/75C,’’ it is intended that 75?C insulated wire may be used at full 75?C ampacity. Where the connection is made to a circuit breaker or switch within the equipment, such a circuit breaker or switch must also be marked for the temperature rating of the conductor.

A 75?C conductor temperature marking on a circuit breaker or switch normally intended for wire sizes 14-1 AWG does not in itself indicate that 75?C insulated wire can be used unless 1) the circuit breaker or switch is used by itself, such as in a separate enclosure, or 2) the equipment in which the circuit breaker or switch is installed is also so marked.

A 75 or 90?C temperature marking on a terminal (e.g., AL7, CU7AL, AL7CU or AL9, CU9AL, AL9CU) does not in itself indicate that 75 or 90?C insulated wire can be used unless the equipment in which the terminals are installed is marked for 75 or 90?C.

Higher temperature rated conductors than specified may be used if the size is based on the above statements.
…

Whether 110.14(C) is an adequate summary of the above I will leave to others (until the 2014 cycle )

I believe the fundamental rule in 110.14(C) is exceptionally confusing:

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.

It should say something like:

The ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any device, appliance, utilization, distribution or control equipment termination.

The emphasis should be that the “coordinated” temperature “…termination provisions are based on [NOT requiring] the use of 60?C insulated conductors in circuits rated 100 A or less, and the use of 75?C insulated conductors in higher rated circuits as specified in Table 310.16 of the NEC” except as specifically provided for elsewhere. There should also be a reference to 310.15(A)(2) indicating other potential conductor ampacity limitations.

 

[hardworkingstiff]

Thanks Bob

Thanks Bob

Thanks for responding Bob.

So, basically, there is no way to use the ampacities of 400.5(B) when one end of the cable conductors are terminated to a breaker and the other end is terminated to a busbar in the marine power center.

 

[rbalex]

Thanks for responding Bob.

So, basically, there is no way to use the ampacities of 400.5(B) when one end of the cable conductors are terminated to a breaker and the other end is terminated to a busbar in the marine power center.

Although I don?t believe it says it very well, in my opinion, it is the intended meaning of the principal rule in 110.14(C).

From a basic physics/philosophy position, a given conductor, either building wire, flexible cord or cable, can and often does have several computed or tabular ampacities. In general, the lowest one trumps the others unless 310.15(A)(2) Exception applies. Technically, that Exception only applies to conductors in Tables 310.16 through 310.21 and not terminations anyway. Since there is no analogous Exception for flexible cords, 110.14(C) becomes the prevailing rule and the circuit breaker terminals are probably the limiting case.

 

[SG-1]

Thanks for responding Bob.

So, basically, there is no way to use the ampacities of 400.5(B) when one end of the cable conductors are terminated to a breaker and the other end is terminated to a busbar in the marine power center.

If I understand correctly I can use Table 400.5(B) as follows to determine the ampacity of a 4/0 cable.

I have a Type W 4/0 four conductor cable with three current carrying conductors.
One end is connected to a bus bar with a temperature rating of 90C.
The other end is connected to a circuit breaker with a temperature rating of 75C.

I use the 75C F3 column and determine that the 4/0 cable can be loaded to 277 amps at 30C ambient and not exceed the temperature rating of the breaker.

I have to make sure I do not exceed the temperature rating of the lower rated device, in this case the breaker.

I bet Eaton is using the 90C column for everything.

 

[rbalex]

...
I bet Eaton is using the 90C column for everything.

It is quite probable they are, but that is the difference between a manufacture's product design and a field installation. In truth, most circuit breakers in this application could handle 90?C conductors with no problem; I just can't design or install it that way.

P.S. You understand correctly.

 

[hardworkingstiff]

What I don't understand is why the W cable according to 400.5(B) has so much of a higher ampacity as the same size conductor at the same temperature according to 310.16.

I understand 310.17 because it's a single conductor in free air, but a W cable is bundled into a cord, sort of like being in a conduit.

Edit: Doesn't 400.5(B) ampacity pretty much say that at that ampacity the cable (and thus the termination) would not exceed the temperature that the ampacity is listed under?

 

[rbalex]

What I don't understand is why the W cable according to 400.5(B) has so much of a higher ampacity as the same size conductor at the same temperature according to 310.16.

I understand 310.17 because it's a single conductor in free air, but a W cable is bundled into a cord, sort of like being in a conduit.

Edit: Doesn't 400.5(B) ampacity pretty much say that at that ampacity the cable (and thus the termination) would not exceed the temperature that the ampacity is listed under?

It?s the same reason that a 90?C conductor has a higher tabular ampacity ? it?s simply a characteristic of the conductor?s insulation under a specified ?condition of use.? Review the definition of ampacity and note any given conductor may have multiple ?conditions of use.?

What 110.14(C) is (attempting) to say is the ?condition of use? for any conductor at the terminals of the Category Code AALZ equipment of interest is based on the Table 310.16 values for a 60?C or 75?C conductor whichever is appropriate. The terminal has no idea what the conductor's insulation is.

 

[Smart $]

...The terminal has no idea what the conductor's insulation is. [/COLOR]

...nor does it have any idea it's condition of use.

The whole problem is the conductor's maximum operating temperature at the termination is not [always] the same as the manner which 110.14(C) prescribes.

 

[rbalex]

...nor does it have any idea it's condition of use.

The whole problem is the conductor's maximum operating temperature at the termination is not [always] the same as the manner which prescribes.

I'm not entirely sure what you are driving at, but I genuinely would like a clarifying example. [And I expect you to help me develop the 2014 Proposal ]

I agree 110.14(C) isn't clear; but the UL White Book is clear enough that, with respect to the terminations 110.14(C) was originally intended to cover, the "condition of use" was the termination connection and the only relevant factors to determine the conductor's maximum ampacity at the termination are the conductor size and the ambient temperature. The addition of the reference to 310.15(B)(6) really muddied the waters.

 

[Smart $]

[And I expect you to help me develop the 2014 Proposal ]

I'll be glad to help.

I'm not entirely sure what you are driving at, but I genuinely would like a clarifying example. ...

I agree 110.14(C) isn't clear; but the UL White Book is clear enough that, with respect to the terminations 110.14(C) was originally intended to cover, the "condition of use" was the termination connection and the only relevant factors to determine the conductor's maximum ampacity at the termination are the conductor size and the ambient temperature. The addition of the reference to 310.15(B)(6) really muddied the waters.

Yes, the UL whitebook language is clear enough, but it assumes a conductor's temperature is or will be based on Table 310.16 (which will likely be Table 310.15(B)(16) when 2014 proposals are submitted). That is fine for testing terminations... as most empirical data is useless without control on parameters. However, we are not so blessed (or cursed) with all installations being based on Table 310.16. There are obviously some based on 310.15(B)(6). The easing of restrictions to permit 310.15(B)(6) does muddy the water, but at the same time indicates the CMP is at least a little flexible on the matter. A proposal to further lift the restriction of 110.14(C) might best be served by expanding on the same concept under which the CMP accepted the addition of 310.15(B)(6)... but at present I am uncertain what that was.

Ultimately, the point of contention is the conductor type and the condition(s) of its usage will affect the temperature-current relationship during operation. That relationship is the very reason other ampacity tables exist. Yet those same variables which justify the other Tables should also be used to determine the conductor's temperature at its termination, should another Table apply at the conductor's termination or immediately adjacent thereto.

Examples are plentiful... so pick one if you must. hardworkingstiff's marina power scenario with Type W flexible cable is but one. Another more general one is spaced single conductors or cables in cable tray (i.e. installed direct to equipment; no raceway transition) whose ampacities are determined by Tables 310.17 or 310.18.

 

[jeffhornsby]

I second the War Eagle
My guess is it is cheaper to make one type rated busbar than a bunch of different rated busbars. also encloed areas will build up heat

Without going into the physics unless you want me to send you paper with the calculations

The higher rated ampacity will just help dissapate the heat.

The actual heat at the terminals is the result of the load.

Think about the all factors that can add heat to circuit,conductors in a raceway, ambient, etc... by using a higher rated ampacity that conductor is able to disspate the heat away from the terminal, which address the added heating between the termination points.

If you feed a 100000000000 rated terimanl from 75 rated breaker 110.14 is not affected it just limits the the the temperature of the circuit not to exceed 75C

You basiclly just cordinate between 310.15 and 110.14

Simply 110.14 sets the temperature limitations of the circuit.

Side note that is why you have exceptions like 210.19 where breakers rated at 100% you do not have to add 125% of continous loads

 

[rbalex]

Is it really so difficult to understand that a terminal doesn?t give a damn about any other condition of use a conductor may have except at the termination? And for a specific conductor material at a continuous current for terminals intended to be covered by 110.14(C), a terminal?s temperature is not affected by anything except the ambient temperature, the conductor?s size, and (rarely) the conductor?s stranding? The conductor?s insulation, i.e. ?Type,? is irrelevant at the termination.

Section 110.14(C) does not intend to impose a general temperature limit on a conductor throughout the circuit and would not were it not for misunderstandings caused by its poor wording; it intends to impose a temperature limit on the conductor at the termination ONLY, and then only for specific classes of equipment.

Section 310.15(B)(6) was originally introduced in the 2002 cycle and included 310.15(B)(1) through 310.15(B)(6). It was intended to clarify that the conductor's ampacity could be ?appropriately modified? throughout the rest of the circuit based on its own temperature rating or specific use. In 2005, Sections 310.15(B)(1) through 310.15(B)(5) were dropped because 310.15(B)(6) was the only ?appropriate modification? that applied solely at the termination.

All 310.15(B)(6) does is recognize a specific set of conditions of use where the conductor loading is known not to be not continuous and the terminations involved will not exceed their temperature rating.

 

[Smart $]

I second the War Eagle
My guess is it is cheaper to make one type rated busbar than a bunch of different rated busbars. also encloed areas will build up heat

Without going into the physics unless you want me to send you paper with the calculations

The higher rated ampacity will just help dissapate the heat.

The actual heat at the terminals is the result of the load.

Think about the all factors that can add heat to circuit,conductors in a raceway, ambient, etc... by using a higher rated ampacity that conductor is able to disspate the heat away from the terminal, which address the added heating between the termination points.

If you feed a 100000000000 rated terimanl from 75 rated breaker 110.14 is not affected it just limits the the the temperature of the circuit not to exceed 75C

You basiclly just cordinate between 310.15 and 110.14

Simply 110.14 sets the temperature limitations of the circuit.

Side note that is why you have exceptions like 210.19 where breakers rated at 100% you do not have to add 125% of continous loads

The concept of 110.14(C) is not being debated. What is being debated is its implementation... more specifically, the coordination and selection of conductor size according to its temperature-current curve.

Your statement, "The higher rated ampacity will just help dissapate the heat", is incorrect if you are referring to a wire size falling within the same ampacity table. For example, a 90?C rated 6 AWG conductor will not [significantly] dissipate any more heat than does a 75?C rated 6 AWG conductor if the ampacity is determined under Table 310.16. The conductor ratings serve to indicate the conductor insulation's thermal degradation characteristic, not its ability to dissipate heat. However, the conductor's ampacity rating is an indication of the ability to dissipate heat under the conditions of installation, i.e. the wiring method.

If you compare the ampacity of say a 6 AWG copper conductor under Table 310.16 to the same size under 400.5(B) you will see values for 75?C-rated conductors listed respectively at 65 and [95, 88, -] 77. These values signify the conductor temperature when a specific amount of current is being conducted and how much the temperature can vary while operating under the different conditions of installation. The relative increase or decrease (as in some cases) in conductor temperature is currently not permitted to be coordinated into the selection of a properly sized conductor for conditions of installation other than those falling under 310.15(B)(6) and Table 310.16.