continuous+conditions

(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 I_Z
[ 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

• длительно допустимый ток
• допустимый ток

EN

• ampacity (US)
• continuous current
• continuous current-carrying capacity
• current-carrying capacity

DE

• Dauerstrombelastbarkeit, f
• Strombelastbarkeit, f

FR

• courant admissible, m
• courant permanent admissible, m

прибор класса II
Прибор, в котором защита от поражения электрическим током обеспечивается не только основной изоляцией, но в котором предусмотрены дополнительные меры безопасности, такие как двойная или усиленная изоляция, причем не предусмотрено защитное заземление, а условия установки не являются дополнительной гарантией.
Примечания:
  1. Такие приборы могут быть отнесены к одному из следующих типов:
a) прибор, имеющий прочный и практически сплошной кожух из изоляционного материала, который покрывает все металлические части, за исключением небольших деталей, таких как заводская табличка, винты и заклепки, которые изолированы от токоведущих частей изоляцией, по крайней мере эквивалентной усиленной изоляции;
такой прибор называют прибором класса II с изолирующим кожухом;
b) прибор, имеющий практически сплошной металлический кожух, в котором повсюду применена двойная или усиленная изоляция; такой прибор называют прибором класса II с металлическим кожухом;
c) прибор, являющийся комбинацией типов, указанных в перечислениях а) и b).
  2. Кожух прибора класса II с изолирующим кожухом может образовывать часть или всю дополнительную или усиленную изоляцию.
  3. Если прибор, имеющий повсюду двойную или усиленную изоляцию, снабжен заземляющим зажимом или заземляющим контактом, то его относят к приборам класса 0 или 0I.
[ ГОСТ Р 52161. 1-2004 ( МЭК 60335-1: 2001)]

EN

class II appliance
appliance in which protection against electric shock does not rely on basic insulation only but in which additional safety precautions are provided, such as double insulation or reinforced insulation, there being no provision for protective earthing or reliance upon installation conditions
NOTE 1 - Such an appliance may be of one of the following types:
– an appliance having a durable and substantially continuous enclosure of insulating material which envelops all metal parts, with the exception of small parts, such as nameplates, screws and rivets, which are isolated from live parts by insulation at least equivalent to reinforced insulation; such an appliance is called an insulation-encased class II appliance;
– an appliance having a substantially continuous metal enclosure, in which double insulation or reinforced insulation is used throughout; such an appliance is called a metal-encased class II appliance;
– an appliance which is a combination of an insulation-encased class II appliance and a metal-encased class II appliance.
NOTE 2 - The enclosure of an insulation-encased class II appliance may form a part or the whole of the supplementary insulation or of the reinforced insulation.
NOTE 3 - If an appliance with double insulation or reinforced insulation throughout has provision for earthing, it is considered to be a class I appliance or a class 0I appliance.
[IEC 60335-1, ed. 4.0 (2001-05)]

FR

appareil de la classe II
appareil dans lequel la protection contre les chocs électriques ne repose pas uniquement sur l'isolation principale mais dans lequel ont été prises des mesures supplémentaires de sécurité, telles que la double isolation ou l'isolation renforcée, ces mesures ne comportant pas de moyen de mise à la terre de protection et ne dépendant pas des conditions d'installation
NOTE 1 - Un tel appareil peut être de l'un des types suivants:
– un appareil ayant une enveloppe durable et pratiquement continue en matière isolante enfermant toutes les parties métalliques, à l'exception de petites pièces telles que plaques signalétiques, vis et rivets, qui sont séparées des parties actives par une isolation au moins équivalente à l'isolation renforcée; un tel appareil est appelé appareil de la classe II à enveloppe isolante;
– un appareil ayant une enveloppe métallique pratiquement continue, dans lequel la double isolation ou l'isolation renforcée est partout utilisée; un tel appareil est appelé appareil de la classe II à enveloppe métallique;
– un appareil qui est la combinaison d’un appareil de la classe II à enveloppe isolante et d’un appareil de la classe II à enveloppe métallique.
NOTE 2 -  L'enveloppe d'un appareil de la classe II à enveloppe isolante peut former tout ou partie de l'isolation supplémentaire ou de l'isolation renforcée.
NOTE 3 - Si un appareil ayant en toutes ses parties une double isolation ou une isolation renforcée comporte des dispositions en vue de la mise à la terre, il est considéré comme étant un appareil de la classe I ou un appareil de la classe 0I.
[IEC 60335-1, ed. 4.0 (2001-05)]

Тематики

• прибор электрический
• электробезопасность

EN

• class II appliance

FR

• appareil de la classe II