BS IEC 60943:1998 pdf download – Guidance concerningthe permissible temperature rise forparts of electrical equipment, in particular for terminals

BS IEC 60943:1998 pdf download – Guidance concerningthe permissible temperature rise forparts of electrical equipment, in particular for terminals.
This report is intended for guidance in estimating the permissible values for temperature and temperature rise of component parts of electrical equipment carrying current under steady state conditions. This report applies to electrical power connections and materials adjacent to them,
This report is concerned with the thermal effects of currents passing through connections, therefore there are no voltage limits to its application.
This report is only applicable when referred to in the appropriate product standard.
The extent and manner to which the contents of this report are used in standards is the responsibility of individual Technical Committees.
Whenever “permissible” values are stated in this report, they mean values permitted by the relevant product standard.
The present report is intended to supply:
general data on the structure of electric contacts and the calculation of their ohmic resistance;
— the basic ageing mechanisms of contacts:
— the calculation of the temperature rise of contacts and connection terminals;
— the maximum “permissible” temperature and temperature rise for various components, in particular
the contacts, the connection terminals and the conductors connected to them:
— the general procedure to be followed by product committees for specifying the permissible
temperature and temperature rise.
1.2 Reference documents
IEC 600.50(441):1984, International Electrotechnical Vocabulary (1EV) — Chapter 441: Switchgear and cant rolgear and fuses.
IKC 60085:1984, Thermal evaluation and classification of electrical insulation.
IKC 60216-1:1990, Guide for the determination of thermal endurance properties of electrical insulating materials — Part 1: general guidelines for ageing procedures and evaluation of the test results. IKC 60364-4-42:1980, Electrical installations of buildings — Part 4: Protection for safety — Chapter 42: Protection against thermal effects.
I EC 60694:1996, L’om mon specifications for high-voltage switchgear and controlgear standards. IEC 60721.2-1:1982, Classification of environmental conditions — Part 2: environmental conditions appearing in nature l’cmperature and humidity.
IEC 60890:1987, A method of temperature-rise assessment by extrapolation for partially type-tested assemblies (PTTA) of low voltage switchgear and controlgear.
IKC 60947.1:1988, Low-voltage switchgear and conirolgear — Part 1: General rules.
1.3 Definitions
Definitions of terms used in this report may be found in the International Electrotechnical Vocabulary. For the purposes of this technical report, the following terms also apply:
1.3.1
ambient air temperature 8
the temperature, determined under prescribed conditions, of the air surrounding the complete device [1EV 44 1.11-131
NOTE For devices installed inside an enclosure, it is the temperature of the air outside the enclosure.
1.3.2
contact (of a mechanical switching device)
conductive parts designed to establish circuit continuity when they touch and which, due to their relative motion during an operation, open or close a circuit or. in the case of hinged or sliding contacts, maintain circuit continuity [1EV 441-15-051
NOTE Do not confuse with 1EV 441.15.06 Contact (pike): one of the conductive parts forming a contact.
2 General considerations concerning the nature of electric contact and the
calculation and measurement of the ohmic resistance of contacts
2.1 Electric contacts and connection terminals
Electric contact, in its simplest and most general configuration, results from contact established between two pieces of (usually metallic) conducting material. In the case of connection terminals, these are the terminal itself and the conductor which is connected to it.
The active zone is the contact “interface” which is the region where the current passes from one piece to the other. It is in this area that the contact resistance occurs. causing heating by Joule effect, and it is also where ageing occurs through chemical reaction with the surrounding atmosphere.
2.2 Nature of electric contact
When one piece of metal is applied to another, contact is not made over the whole apparent contact area, but only at a certain number of points called “elementary contacts”.
The effective total cross.sectional area of these contacts is equal to the effective contact area S11 if the possible presence of impurities is ignored (dust, etc.) at the contact interface.
There is also a fine layer of air or of oxide normally present, the effect of which upon the contact resistance will be examined later (see 2.3).
In the following, for ease of calculation and for a better understanding of the contact mechanisms, the simplifying assumption is made that there are n elementary contacts on the apparent contact area, uniformly distributed, of average constant radius a (see Figure 1). The average distance between these elementary contacts is I.