There are several test methods in use by the industry to determine this temperature. They generally involve cooling the wire to a specified temperature (–25° C is typical) and then bending the wire around a mandrel whose diameter is in the range of 4 to 8 times the wire diameter.
Full Answer
How do you test the temperature of a wire?
They generally involve cooling the wire to a specified temperature (–25° C is typical) and then bending the wire around a mandrel whose diameter is in the range of 4 to 8 times the wire diameter. Details of one such test method are given in Section 7.5 of UL Standard 2556.
What is the temperature rating of a cable?
This is the temperature rating that most cable users think of first. It is usually defined as the maximum continuous temperature that the wire can withstand during its lifetime. It is generally limited by the thermal aging characteristics of the polymers, i.e., the plastics used to insulate and/ or jacket the wire.
What is the minimum cold Bend rating for wire?
The minimum cold bend rating for wire is usually defined as the lowest temperature at which it can be bent without cracking under specific laboratory conditions. There are several test methods in use by the industry to determine this temperature.
Who is responsible for wire size and temperature ratings?
While the ultimate authority on wire size, temperature ratings, and conduit fill is the project electrical engineer, and then the local inspector, we thought it would be useful to present some key points to help explain wire temperature ratings.
What is the temperature rating of a wire?
The higher a material's heat resistance, the less likely it will deteriorate in higher temperatures. The most common conductor temperature rating is 90°C, but conductors can be rated as low as 60°C or as high as 1,200°C for some special purpose wire and cables.
What is a temperature rating?
The temperature rating is a measurement of a tire's resistance to heat generation under normal operating conditions at recommended inflation pressures. Temperature grades range from A to C, with A being highest rated and therefore most resistant to heat generation.
How do you find ampacity with temperature?
Therefore, the Table 310.15(B)(2)(a) correction factor, in the 90°C column, for an ambient temperature of 35°C is 0.96. To find the minimum ampacity, divide the actual load by the adjustment and correction factors. After dividing the load of 119A by the adjustment factor, the ampacity is 170A (119 ÷ 0.70 = 170).
How does temperature affect wire size?
The higher the temperature rating, the greater the ampacity for a given AWG size (gauge) of conductor.
What is T6 temperature rating?
A rating of T6 means the maximum surface temperature generated by the equipment is 85° C. Assuming the associated T Class and Temperature rating for the equipment are appropriate for the area, you can always use an instrument with a more stringent Division rating than required for the area.
What is T4 temperature rating?
Temperature ClassificationsCLASSSURFACE TEMPERATURE °CT1<450T2<300T3<200T4<1352 more rows•Apr 8, 2019
Does ampacity increase with temperature?
Similarly, the higher the temperature resistance of the insulating material, the higher the ampacity or current carrying capacity.
What determines ampacity of a wire?
NUMBER OF CURRENT-CARRYING CONDUCTORS: The number of current-carrying conductors in a wiring method can affect the ampacity of the conductors. NEC® Table 310.15(B)(16) ampacities are based on no more than three current-carrying conductors.
How do you calculate the current wire capacity?
For Cable Current Capacity = 4X Size of Cable in Sq.mm, Ex. For 2.5 Sq.mm = 4×2.5 = 9 Amp.
What temp is Thhn wire good for?
194°F.THHN is bare stranded copper with a nylon jacket over the PVC insulation. It is rated for use up to 600 Volts and temperatures up to 194°F.
What would a cable rating of 6 3 represent?
The 6 3 copper wire amp rating is typically 55 amps. But heat can also change the 6 3 wire amp rating, for there's a relationship between temperature and the wire's current carrying capacity. For example, a 6 3 wire with ground might have a reduced amperage carrying capacity of 50 amps.
Is 37.6 a fever?
Your normal body temperature is approximately 37C. A fever is usually when your body temperature is 37.8C or higher.
Is 37.5 a fever?
An adult probably has a fever when the temperature is above 99°F to 99.5°F (37.2°C to 37.5°C), depending on the time of day.
Is 37.4 a fever?
What are the symptoms of a fever? Normal body temperature ranges from 97.5°F to 99.5°F (36.4°C to 37.4°C). It tends to be lower in the morning and higher in the evening. Most healthcare providers consider a fever to be 100.4°F (38°C) or higher.
Is 98.0 considered a fever?
While body temperatures vary, most of us have an internal temperature around 98.6 degrees Fahrenheit. A temperature slightly higher than that is still normal. When your temperature is between 100.4 and 102.2, you have what is considered a low grade fever.
What is the temperature rating of wire?
This is the temperature rating that most cable users think of first. It is usually defined as the maximum continuous temperature that the wire can withstand during its lifetime. It is generally limited by the thermal aging characteristics of the polymers, i.e., the plastics used to insulate and/ or jacket the wire. The metallic components of the wire seldom limit the temperature rating except in high-temperature wire where oxidation of the metal begins to become a significant factor at approximately 250° C.
What temperature does a polymer crack?
Depending on polymer type, they begin to crack when bent at temperatures ranging from –10° C down to approximately –80° C. The minimum cold bend rating for wire is usually defined as the lowest temperature at which it can be bent without cracking under specific laboratory conditions. There are several test methods in use by the industry to determine this temperature. They generally involve cooling the wire to a specified temperature (–25° C is typical) and then bending the wire around a mandrel whose diameter is in the range of 4 to 8 times the wire diameter. Details of one such test method are given in Section 7.5 of UL Standard 2556. [2]
How does thermal aging affect wire life?
Every polymer has its own unique thermal aging characteristics. However, as a rule-of-thumb, for every 10° C the operating temperature of a polymer is increased, the life is decreased by a factor of two. For example, a wire that is designed to survive 40 years at 90° C would be expected to survive only 20 years at 100° C and 10 years at 110° C. The mathematical model used to calculate the relationship between temperature and cable life is called the Arrhenius relationship [1] after the Swedish chemist that developed it. The Arrhenius relationship coupled with field experience and laboratory aging tests are the basis for the operating temperature rating assigned to most wire and cable products.
How long can a 90°C cable last?
For example, many 90° C rated power cables have an emergency overload rating which permits their use at 130° C for a total of up to 500 hours during their lifetime. Generally, these cables also have a short circuit rating which is the highest temperature ...
What is the bottom line of temp rating?
the bottom line for temp rating is in the fact that heat, from an element rises, and makes older wire with lower temp ratings insulation deteriorate.
How much 90 deg NM wire should I use for a fixture?
if you have a accessable space behind the location you are to mount said fixture ( an attic, etc) i suggest you use a few feet of 90 deg NM wire and junction it to your older wire.
What is the temperature rating of a flourescent?
You will normally find the 90 C. temprature rating of the wiring required when that wire enters the recessed fixture or inside the case of a flourescent fixture. Locations inside a recessed fixture has an increased temprature causing concern of that 60 C wire to be damaged due to that heat contained within that recessed fixture. Flourescent fixtures have the same increased heat problem due to the thermally protected ballast installed inside that flourescent fixture. This ballast gets hot enough to cause heat damage to 60 C rated wire but not hot enough to damage 90 C wire.
What type of wire is used for AC?
Type AC cable has a thin metal strip ensuring the use of the flexible metal sheathing to have a grounding integrity but does not usually have the green wire installed. The thin metal strip along with the flexible metal sheathing cobined acts as a grounding source for that cable.
Is there a 90 C rating for incandescent lights?
You will seldom if ever find a 90 C rating requirement to connect a surface mounted incandescent fixture due to that fiberglass insulation being considered as a heat shield allowing the 60 C wiring to be installed.
Can I connect a 60°C bulb to a 90°C wire?
So it sounds like the problem is the heat created by the bulb could have a harmful effect on the wiring; it has nothing to do with the current flowing through the wire itself. If that's the case, then I ought to be able to go into the attic, disconnect the existing 60°C wire from the fixture box, insert a section of 90°C wire between the existing 60°C wire and the fixture box, and re-connect the fixture. As long as the 60°C wire isn't close to the fixture itself, there shouldn't be a problem. Thanks.
How to find temperature over different conditions?
Probably the best way to find the temperature over different conditions is to measure it. You can calculate the resistance as a function of temperature from the resistivity of nichrome, which is something you should be able to look up. Create a setup that regulates the power going into the wire and measured voltage and current. From that you can compute resistance, from which you can compute temperature. Now measure that temperature over whatever range of conditions you care about. Important variables will be air speed, orientation, humidity, and pressure.
What variables can you use to calculate resistance?
Now measure that temperature over whatever range of conditions you care about. Important variables will be air speed, orientation, humidity, and pressure. Look up something called a hot wire anemometer.
Is it impossible to calculate a number instead of measuring it?
If you insist on calculating it instead of measuring it, it is not impossible but way more troublesome than measuring it.
Can you analyze your exact situation more closely?
It is , of course, possible to analyze your exact situation much more closely, with hard numbers predicted, but you still need to verify the predictions with careful measurement. A good example is here:
Does wire need to be hot to create air flow?
This will greatly depend on air flow, which you haven't specified. In addition to that, the wire will be hot enough to create its own air flow in still air, and that will depend on the orientation of the wire, which is yet another thing you haven't specified.
What is the rated temperature for 90 lugs?
Manufacturers commonly use 90°C-rated lugs (i.e., marked AL9CU) on equipment rated only 60°C or 75°C. The use of the 90°C-rated lug in this type of equipment does not allow the installer to use 90°C wire at the 90°C ampacity.
What temperature should a termination be?
When terminations are inside equipment such as panelboards, motor control centers, switchboards, enclosed circuit breakers, safety switches, etc., follow the temperature rating identified on the equipment labeling instead of the rating of the lug itself. Manufacturers commonly use 90°C-rated lugs (i.e., marked AL9CU) on equipment rated only 60°C or 75°C. The use of the 90°C-rated lug in this type of equipment does not allow the installer to use 90°C wire at the 90°C ampacity. The Underwriters Laboratories® General Information on Electrical Equipment Directory states the following about terminations: “A 75°C or 90°C temperature marking on a terminal (e.g., AL7, CU7AL, AL7CU or AL9, CU9AL, AL9CU) does not in itself indicate that a 75°C or 90°C insulated wire can be used unless the equipment in which the terminals are installed is marked for 75°C or 90°C.”
What About Higher-Rated Conductors and Derating Factors?
One advantage to conductors with higher insulation ratings is noted when derating factors are applied . This advantage is noted in the last sentence of NEC 110.14 (C): “Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both.” Derating factors may be required because of the number of conductors in a conduit, higher ambient temperatures, or internal design requirements for a facility. By beginning the derating process at the ampacity of the conductor based on the higher insulation value, you may not be required to upsize the conductor to compensate for the derating.
What is the ampacity of 300 kcmil copper?
300 kcmil copper has a 75°C ampacity of 285 A.
How many conductors can be terminated in a single terminal?
The NEC contains some key references regarding how many conductors can be terminated in a single terminal. NEC 110.14 (A) has a blanket statement requiring that terminals for more than one conductor shall be so identified. This would mean that the terminal (or terminal bar) would have to be identified to accept more than one conductor. For equipment that contains a terminal or terminal bar, this identification is generally found on the wiring diagram or some other label on or inside the product.
What is the ampacity value determined after applying the derating factors?
The ampacity value determined after applying the derating factors must be equal to or less than the ampacity of the conductor based on the temperature limitations at its terminations.
Why is it important to terminate a conductor?
Proper termination of conductors is a critical part of having a safe electrical installation. Assigning the ampacity of a conductor is impacted by not only the physical characteristics of the conductor, but the connected equipment as well. Closely adhering to the NEC rules will not only avoid rejected installations from inspectors, but will help to avoid having problems with the terminations in the future.
Why is it so hard to calculate the temperature of a wire?
Calculating the temperature rise of a wire is hard (much easier/less time consuming to experimentally verify) why? Because you need to know the thermal conductivity of that specific type of PVC and also how much heating per unit area.
How many amps does a device draw?
A device draws a constant 10 amps at 12 V through the wire.
Does power loss heat wires?
This power 'loss' will try to heat the wire. The natural cooling effect around the wire will tend to cool the wire towards ambient.
