-
1 длительный допустимый ток
- Strombelastbarkeit, f
- Dauerstrombelastbarkeit, f
(длительный) допустимый ток
Максимальное значение электрического тока, который может протекать длительно по проводнику, устройству или аппарату при определенных условиях без превышения определенного значения их температуры в установившемся режиме
[ ГОСТ Р МЭК 60050-826-2009]
Этот ток обозначают IZ
[ ГОСТ Р 50571. 1-2009 ( МЭК 60364-1: 2005)]EN
(continuous) current-carrying capacity
ampacity (US)
maximum value of electric current which can be carried continuously by a conductor, a device or an apparatus, under specified conditions without its steady-state temperature exceeding a specified value
[IEV number 826-11-13]
ampacity
The current in amperes that a conductor can carry continuously under the conditions of use without exceeding its temperature rating.
[National Electrical Cod]FR
courant (permanent) admissible, m
valeur maximale du courant électrique qui peut parcourir en permanence, un conducteur, un dispositif ou un appareil, sans que sa température de régime permanent, dans des conditions données, soit supérieure à la valeur spécifiée
[IEV number 826-11-13]Ampacity, the term is defined as the maximum amount of current a cable can carry before sustaining immediate or progressive deterioration. Also described as current rating or current-carrying capacity, is the RMS electric current which a device can continuously carry while remaining within its temperature rating. The ampacity of a cable depends on:
- its insulation temperature rating;
- conductor electrical properties for current;
- frequency, in the case of alternating currents;
- ability to dissipate heat, which depends on cable geometry and its surroundings;
- ambient temperature.
Electric wires have some resistance, and electric current flowing through them causes voltage drop and power dissipation, which heats the cable. Copper or aluminum can conduct a large amount of current before melting, but long before the conductors melt, their insulation would be damaged by the heat.
The ampacity for a power cable is thus based on physical and electrical properties of the material & construction of the conductor and of its insulation, ambient temperature, and environmental conditions adjacent to the cable. Having a large overall surface area may dissipate heat well if the environment can absorb the heat.
In a long run of cable, different conditions govern, and installation regulations normally specify that the most severe condition along the run governs the cable's rating. Cables run in wet or oily locations may carry a lower temperature rating than in a dry installation. Derating is necessary for multiple circuits in close proximity. When multiple cables are near, each contributes heat to the others and diminishes the amount of cooling air that can flow past the individual cables. The overall ampacity of the insulated conductors in a bundle of more than 3 must be derated, whether in a raceway or cable. Usually the de-rating factor is tabulated in a nation's wiring regulations.
Depending on the type of insulating material, common maximum allowable temperatures at the surface of the conductor are 60, 75 and 90 degrees Celsius, often with an ambient air temperature of 30°C. In the U.S., 105°C is allowed with ambient of 40°C, for larger power cables, especially those operating at more than 2 kV. Likewise, specific insulations are rated 150, 200 or 250°C.
The allowed current in cables generally needs to be decreased (derated) when the cable is covered with fireproofing material.
For example, the United States National Electric Code, Table 310-16, specifies that up to three 8 AWG copper wires having a common insulating material (THWN) in a raceway, cable, or direct burial has an ampacity of 50 A when the ambient air is 30°C, the conductor surface temperature allowed to be 75°C. A single insulated conductor in air has 70 A rating.
Ampacity rating is normally for continuous current, and short periods of overcurrent occur without harm in most cabling systems. The acceptable magnitude and duration of overcurrent is a more complex topic than ampacity.
When designing an electrical system, one will normally need to know the current rating for the following:- Wires
- Printed Circuit Board traces, where included
- Fuses
- Circuit breakers
- All or nearly all components used
Some devices are limited by power rating, and when this power rating occurs below their current limit, it is not necessary to know the current limit to design a system. A common example of this is lightbulb holders.
[http://en.wikipedia.org/wiki/Ampacity]
Тематики
- электротехника, основные понятия
Синонимы
EN
DE
- Dauerstrombelastbarkeit, f
- Strombelastbarkeit, f
FR
- courant admissible, m
- courant permanent admissible, m
Русско-немецкий словарь нормативно-технической терминологии > длительный допустимый ток
См. также в других словарях:
Insulating concrete forms — ( ICFs ) are stay in place formwork for energy efficient, cast in place reinforced concrete walls.The forms are interlocking modular units that are dry stacked (without mortar) and filled with concrete. The forms lock together somewhat like Lego… … Wikipedia
R-value (insulation) — The R value or R value is a measure of thermal resistance (K·m²/W) [Oak Ridge National Laboratory, [http://www.ornl.gov/sci/roofs+walls/insulation/ins 02.html Which Kind Of Insulation Is Best?] , retrieved 2008 07 13.] used in the building and… … Wikipedia
R-Value — A measure of the capacity of a material to resist heat transfer. The R Value is the reciprocal of the conductivity of a material (U Value). The larger the R Value of a material, the greater its insulating properties. *** A measure of a… … Energy terms
u-value — ˈ ̷ ̷ ¦ ̷ ̷ (ˌ) ̷ ̷ noun Usage: usually capitalized U Etymology: from unit : a measure of the heat transmission through a building part (as a wall or window) or a given thickness of a material (as insulation) with lower numbers indicating better… … Useful english dictionary
U-value — /yooh val yooh/, n. a measure of the flow of heat through an insulating or building material: the lower the U value, the better the insulating ability. Cf. R value. [1945 50; U, symbol for internal energy] * * * … Universalium
U-value — U val•ue [[t]ˈyuˌvæl yu[/t]] n. bui a measure of the flow of heat through an insulating or building material: the lower the U value, the better the insulating ability Compare R value • Etymology: 1945–50; U, symbol for internal energy … From formal English to slang
R-value — [är′val΄yo͞o] n. a measurement indicating the resistance of a given thickness of material, esp. insulating material, to the flow of heat: the higher the R value, the greater the insulation … English World dictionary
R-value — noun Etymology: probably from thermal resistance Date: 1948 a measure of resistance to the flow of heat through a given thickness of a material (as insulation) with higher numbers indicating better insulating properties compare U value … New Collegiate Dictionary
U-value — noun Etymology: unit Date: 1949 a measure of the heat transmission through a building part (as a wall or window) or a given thickness of a material (as insulation) with lower numbers indicating better insulating properties compare R value … New Collegiate Dictionary
R-value — /ahr val yooh/, n. a measure of the resistance of an insulating or building material to heat flow, expressed as R 11, R 20, and so on; the higher the number, the greater the resistance to heat flow. Cf. U value. [1945 50; R, symbol for… … Universalium
U-Value — (see Coefficient of Heat Transmission) The reciprocal of R Value. The lower the number, the greater the heat transfer resistance (insulating) characteristics of the material … Energy terms
