40deg C Brkrs

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Don Gorham

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I am installing a panelboard and discovered the factory, (SIEMENS) has provided 40deg C rated circuit breakers. Where does the code provide for wire ampacities based on less than 60deg C temperature ratings? This is a 900 amp 480volt, 3ph 3w with various 3p breakers from 60 amp to 100 amp. Thanks gents. Don
 
The 40?C value is the ambient air rating of the breaker. It has nothing to do with the termination temperature rating.

If you have a UL listed breaker, it has terminals rated for use with the NEC.
 
jim dungar said:
The 40?C value is the ambient air rating of the breaker. It has nothing to do with the termination temperature rating.

If you have a UL listed breaker, it has terminals rated for use with the NEC.
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Yes and no.

The terminals are also(normally) rated for 40C ambient. If the breaker is also rated for say 50C the terminals are not automatically rated for the same ambient. The 310 tables are of course all rated to 30C with the adjustment factors listed under those.
 
weressl said:
Yes and no.

The terminals are also(normally) rated for 40C ambient. If the breaker is also rated for say 50C the terminals are not automatically rated for the same ambient. The 310 tables are of course all rated to 30C with the adjustment factors listed under those.
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While the ambient temperature rating applies to the breaker and all of its parts, I am not aware of any breaker with terminations that are not suitable for use with 60?C ampacity conductors.
 
don_resqcapt19 said:
While the ambient temperature rating applies to the breaker and all of its parts, I am not aware of any breaker with terminations that are not suitable for use with 60?C ampacity conductors.
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After Jim's reply that was cleared up. The OP referred to the rise and confused it with the ambient and that is what Jim helped to clear up.

Since you replied to my comment, let me try to make it clear that my point was that your breaker ambient rating, the connector ambient rating and the wire ambient rating all have to match. Isn't the 60C rating you are referring to is the rise, not the ambient?
 
weressl said:
After Jim's reply that was cleared up. The OP referred to the rise and confused it with the ambient and that is what Jim helped to clear up.

Since you replied to my comment, let me try to make it clear that my point was that your breaker ambient rating, the connector ambient rating and the wire ambient rating all have to match. Isn't the 60C rating you are referring to is the rise, not the ambient?
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I don't think it is either a rise or an ambient...the 60?C is related to the ampacity of the conductor. You have to use a conductor that has a 60?C ampacity that is at least equal to the rating of the breaker.
I am not aware of an ambient rating for the connector and the only thing you have to look at for the conductor is the correction factor for the ampacity when the conductor is installed in an ambient other than 30?C.
 
don_resqcapt19 said:
I don't think it is either a rise or an ambient...the 60?C is related to the ampacity of the conductor. You have to use a conductor that has a 60?C ampacity that is at least equal to the rating of the breaker.
I am not aware of an ambient rating for the connector and the only thing you have to look at for the conductor is the correction factor for the ampacity when the conductor is installed in an ambient other than 30?C.
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Ampacity is measured in Amperes not Centigrades.

All electrical equipment and material is rated to operate between a maximum and minimum(sometimes) ambient temperature.

The temperature rating stamped on the conductors refers to the maximum rise of temperature over the ambient temperature that is permitted to occur when operated at rated current for the specific installation method.
 
weressl said:
Ampacity is measured in Amperes not Centigrades.
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Sure it is, but the ampacity of the conductor changes with the temperature.

All electrical equipment and material is rated to operate between a maximum and minimum(sometimes) ambient temperature.
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ok
The temperature rating stamped on the conductors refers to the maximum rise of temperature over the ambient temperature that is permitted to occur when operated at rated current for the specific installation method.
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I don't agree. The temperature on the wire is its maximum permitted operational temperature. If you load a 60?C rated conductor to its maximum permitted ampacity in a 30?C ambient, the temperature of the copper will approach 60?C, not 90?C.
Take a look at the temperature factors at the bottom of T310.26. If you install a 60?C rated conductor in an ambient above 55?C the ampacity of that conductor goes to zero.
 
Temperature ratings are used in enough different ways, that I expect that I've made an error or two herein:

1) The temperature rating of wire (as used in table 310.16 and elsewhere) is the maximum conductor temperature that is permitted in normal operation. (Not temperature _rise_, but temperature.) The numbers given in the table presume a 30C ambient; so for example the 60C column presumes a 30C rise.

2) The temperature rating on a breaker is the ambient temperature at which it is calibrated.

3) The temperature rating of a terminal is the maximum temperature permitted of the conductors connected to that terminal in normal operation, as caused by the combination of ambient conditions and self heating.

4) It seems plausible to me that the terminals on the breaker are also rated for a 40C ambient. If true, this would mean that in addition to the maximum temperature mentioned in 3), there is a further constraint that the ambient conditions prior to any self heating caused by current flow must be 40C or less.

5) Motors and transformers are often rated at a maximum temperature rise in a given ambient condition...which is confusing, because the magnet wire is often rated with a maximum temperature (not rise)

-Jon
 
winnie said:
...
4) It seems plausible to me that the terminals on the breaker are also rated for a 40C ambient. If true, this would mean that in addition to the maximum temperature mentioned in 3), there is a further constraint that the ambient conditions prior to any self heating caused by current flow must be 40C or less.
...
-Jon
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If the breaker terminations are listed for a 40?C ambient and also listed for use with 60?C conductors, would we have to use a correction factor of 0.82 for the conductor ampcity?
 
don_resqcapt19 said:
If the breaker terminations are listed for a 40?C ambient and also listed for use with 60?C conductors, would we have to use a correction factor of 0.82 for the conductor ampcity?
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If the ambient region is below 30C, then no. Just because the breaker can be used in a 40C environment doesn't mean you have to.

If the ambient region is at 40C and is large enough, than yes. If the entire assembly (breaker, enclosure, and a significant length of the conductor) is at 40C, then you apply the temperature adjustment factors at the bottom of table 310.16.

However, as I recall, there are length exceptions for short warm areas of conductors; but I don't remember the details. My 'off the cuff' is that if the breaker enclosure is at 40C (ambient for one breaker as caused by the other breakers) but the rest of the conductor is in a 30C ambient, then no adjustment of conductor ampacity is needed.

Just my HO.

-Jon
 
winnie said:
If the ambient region is below 30C, then no. Just because the breaker can be used in a 40C environment doesn't mean you have to.

If the ambient region is at 40C and is large enough, than yes. If the entire assembly (breaker, enclosure, and a significant length of the conductor) is at 40C, then you apply the temperature adjustment factors at the bottom of table 310.16.

However, as I recall, there are length exceptions for short warm areas of conductors; but I don't remember the details. My 'off the cuff' is that if the breaker enclosure is at 40C (ambient for one breaker as caused by the other breakers) but the rest of the conductor is in a 30C ambient, then no adjustment of conductor ampacity is needed.

Just my HO.

-Jon
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Jon,
I guess I wasn't thinking this morning. The wire does have to be derated based on the ambient that it is installed in. You are also correct about short lengths not needing derating. See the exception to 310.15(A)(2).
Exception: Where two different ampacities apply to adjacent portions of a circuit, the higher ampacity shall be permitted to be used beyond the point of transition, a distance equal to 3.0 m (10 ft) or 10 percent of the circuit length figured at the higher ampacity, whichever is less.
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weressl said:
The temperature rating stamped on the conductors refers to the maximum rise of temperature over the ambient temperature that is permitted to occur when operated at rated current for the specific installation method.
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I think that you may be confusing wire insulation temperature and Motor temperature Rise.

steve
 
weressl said:
Anyone knows if terminals and lugs are also designed for temperature rise - over ambient - or maximum temperature. 75C and 90C ratings?
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It is my understanding that the terminal rating is a maximum, not a rise.

But I can not provide anything to back that up other than the terminals only say '90 C' not '90 C rise'.
 
iwire said:
It is my understanding that the terminal rating is a maximum, not a rise.

But I can not provide anything to back that up other than the terminals only say '90 C' not '90 C rise'.
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I thought it was that way too, but after reading this Square D document I am not so sure.
Underwriter Laboratories Inc. (UL) standards require that molded-case
circuit breakers rated at 125 amperes or less be marked with the conductor
insulation-temperature rating. Table 1 contains a listing of wire temperature
ratings for Square D circuit breakers. The wire temperature rating is
determined by testing the circuit breaker under full-load current with
conductors sized for the appropriate temperature rating?60?C or 75?C. The
temperature rise at the circuit breaker terminals must not exceed 50?C above
ambient per UL Standard 489.
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If the ambient is at the maximum permitted ambient of 40?C and the standard permits a 50?C over the ambient, how can we use 60? or 75?C conductors? They could be operating at 90?C at the termination.
 
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