Clarification on 110.14 (C)(1), 60 vs. 75 degree conductors

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richwaskowitz

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I don't quite understand what is being said here (2005 110.14 (C)(1) (a) an (b). Can anyone clarify please? Is this saying that for circuits rated 100 amps or less, if using 75 degree wire (THW for example) I cannot use the ampacity ratings for 75 degree wire even if the lugs ARE rated 75 degrees, and that I can only use the 75 degree ampacity rating when teh circuit is over 100 amps? In other words, even though table 310.16 lists #6 THW at 65 amps, since the circuit is under 100 amps I can only use the 55 amp, 60 degree rating for THW?
 
Rich, the key is in (C)(1).

(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 310.16 as appropriately modified by 310.15(B)(6).
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Most modern equipment is listed and marked as to it's temperature limitations and that is what would be used.

In a case where the equipment is not listed and marked the general provisions of 110.14(C) would come into play.

Roger
 
Is this saying that for circuits rated 100 amps or less, if using 75 degree wire (THW for example) I cannot use the ampacity ratings for 75 degree wire even if the lugs ARE rated 75 degrees, and that I can only use the 75 degree ampacity rating when teh circuit is over 100 amps?
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No, basically what this says is that if the terminals for a circuit less then 100 amps or conductors smaller thatn 1 AWG are not marked then I must use the 60 degree column. But if the same circuit has all the terminals marked with 75 degrees then I can use the 75 degree column.

Again remeber that even if I have to use the 60 degree column due to the terminal ratings I am still able to use 75 degree column for deration purposes as long as the final ampacity does not exceed the value in the 60 degree column.

Chris
 
Chris / Roger a lot of breakers are stamped 60c / 75c Should one use the lower termination provision for conductor ampacity per Tbl.310.16? Did you ever see a breaker stamped 40c? I thought I had at one time. Just curious.
 
dcspector said:
Did you ever see a breaker stamped 40c?
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I think you will find 40 C on all molded case breakers.

That is the maximum ambient temperature that the breaker is rated for.



a lot of breakers are stamped 60c / 75c Should one use the lower termination provision for conductor ampacity per Tbl.310.16?
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If I recall correctly a breaker marked 60/75C is actually rated for 75 C when used alone and only 60 C when installed in a panel surrounded by other breakers.
 
iwire said:
... If I recall correctly a breaker marked 60/75C is actually rated for 75 C when used alone and only 60 C when installed in a panel surrounded by other breakers.
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Looks like another instance of good recall.

*****************
CIRCUIT BREAKERS (DHJR)
USE
This category covers circuit breakers which, unless otherwise noted, are of
the manually operable, air break type, providing automatic overcurrent protection.
PRODUCT MARKINGS AND RATINGS
These circuit breakers and circuit breaker enclosures are intended for use
with copper conductors unless marked to indicate which terminals are suitable
for use with aluminum conductors. Such markings are independent of
any marking on terminal connectors and are located on a wiring diagram or
another readily visible location.
1. Circuit breaker enclosures are marked to indicate the temperature rating
of all field installed conductors.
2. Circuit breakers with a current rating of 125 A or less are marked as
being suitable for 60?C, 75?C only or 60/75?C rated conductors. It is
acceptable to use conductors with a higher insulation rating, if the
ampacity is based on the conductor temperature rating marked on the
breaker.
3. Circuit breakers rated 125 A or less and marked suitable for use with
75?C rated conductors are intended for field use with 75?C rated conductors
at full 75?C ampacity only when the circuit breaker is installed
in a circuit breaker enclosure or individually mounted in an industrial
control panel with no other component next to it, unless the end-use
equipment (panelboard, switchboard, service equipment, power outlet,
etc.) is also marked suitable for use with conductors rated 75?C.
4. A circuit breaker with a current rating of more than 125 A is suitable
for use with conductors rated 75?C.
5. Circuit breakers intended for continuous operation at 100 percent of
rated current may be marked to be connected with 90?C rated wire
with the size based on 75?C ampacity.
A suitable marking is required in a circuit breaker enclosure, whether or
not terminals are mounted therein, if it is intended that the breaker to be
mounted therein is to be used with aluminum wire.
ADDITIONAL INFORMATION
For additional information, see Electrical Equipment for Use in Ordinary
Locations (AALZ).
 
Bob and Jim. I am now confused. Ok...what they are rated for is if a breaker is stamped 60/75 and used alone then the 75c column would used for conductor ampacity. If in a normal panel used... let's say a 42 CH then one must use the 60c column for ampacity? Or, as usual, am I out in the "corn field"
 
dcspector said:
... Did you ever see a breaker stamped 40c? I thought I had at one time. Just curious ...
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40c is the "standard" temp used when rating a breaker and when drawing-up a breaker's thermal trip curve. (i.e. if it it starts out hotter, it'll trip faster than shown on the curve and vice-versa)

See the description on pg 18 and the 40c annotation of the curves (page 19-on) in the following SQD tech specs. http://ecatalog.squared.com/pubs/Circuit%20Protection/Miniature%20Circuit%20Breakers/0730CT9801.pdf

Maybe that's what the "40" you saw was referring to ???
 
I understood that 60/75 meant that it was suitable for use at either temperature, where the others were suitable for use only at the temperatures listed.

Jim T
 
Greg, a breaker that is rated only 75 deg would not be allowed to have a 60 deg conductor connected to it whereas if the breaker was rated 60/75 you could use a 60 deg conductor at its ampacity.

Look at note # 2 in Novas post.

Roger
 
110.14(C) Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction or both. This is the last sentence of the (C) paragraph and the important words are "shall be permitted ". My interpretation of this is I can use a 90C rating for the wire if it exists, apply whatever derating is necessary in your situation and if the derated ampacity meets the terminal lug ampacity
requirements , you can use the derated conductor.
 
Bob, Jim and Jim......I am now in "Lock Rotor" I know it is not your job to teach me, but I for some reason having and have always have had a problem with understanding this. Sorry. It may be simple to others....but:-?
 
dcspector said:
Bob and Jim. I am now confused. Ok...what they are rated for is if a breaker is stamped 60/75 and used alone then the 75c column would used for conductor ampacity. If in a normal panel used... let's say a 42 CH then one must use the 60c column for ampacity?
Click to expand...
That's how I interpret it too.

I think it's all related to breakers being rated in "free air"

Cram 'em all together at 75c ampacity, heat builds up and begins to adversely affect their ratings ... causing them to trip early (outside of their rated curves).

Using the reduced ampacity avail @ 60c apparently reduces the heat buildup enough so closely-packed breakers still function within their spec'd curve.

At least that's my understanding of it ... standing-by to be "set straight"
 
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Per the quoted UL reference, if the "end use equipment" (ie. a panelboard) has an overall rating of "75C" then it is acceptable for to use the 75C rating on a combination 60/75C breaker. However, if the enlosure is not rated for 75C conductors you cannot exceed the 60C rating regardless of what is marked on the breaker itself.
 
I see this type of confusion out in the field all the time. What usually happens is the installer will just install what he/she wants until someone says something.

One thing to remember 1st. Older equipment is most likely listed at 60C. Newer equipment is listed at 75C or 60/75C.

With that in mind, now we can use 110.14(C)(1)&(2).
If a CB, enclosure, device or other equipment is listed as 60/75C, that means you can use the 75C column of Table 310.16 for the final conductor ampacity.
(most of todays equipment is listed at 60/75C or straight 75C)
Just remember that the enclosure, the CB and the conductor all have to be rated for the 75C. If one component of the circuit is listed for 60C, that is the "weak" link and that would be the column used for ampacity in Table 310.16.

The 40C mentioned earlier is usually stamped on the side of CBs. That is the ambient temperature of the CB. If the ambient temperature of the location of the CB is higher than 40C, than some adjustments for the ampacity of the circuit breaker have to be made. It does not mean that the circuit breaker cannot be installed in higher ambient temperatures. The manufacturer of the CBs will have a chart/table to use as guidance.
 
Thanks Pierre and all, I have always had a tough time with this....40c on the breaker 60c/75c..........:confused: But as I read the posts I think I have a better understanding.
 
I may be dreaming...but...I could swear that I saw a old (ITE maybe?) 20A single pole breaker that was rated for 40C conductors.
I remember it because I had never seen one before and it stuck with me.
It was in a old (40 years+?) breaker panel.
What was the temp rating on the old (cloth covered) nm?

steve
 
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