Temperature of contacts of contactors

[panou]

Hi . I want to make a study about the temperature effect on switchboards. I ahve found enough docs on internet except from one subject :
the temperature of the main contacts of a contactor or a circuit breaker. In all the documentation i have seen specifications for the ambient temperature but not the temperature of the main contacts itself.
Thanks in advance for your time.

 

[RRaghunath]

The codes on switchgear generally stipulate 90degC for bare copper contacts and 105degC for silver plated contacts as the max permissible working temperature.

 

[panou]

rraghunath
Thanks for the reply
Is there any documentation from web where i can see more details.
In all the manufacturers that i have search i have seen that the give only assmbly instructions for the main contacts.

 

[electricpete]

One reference. Go to

http://www.usbr.gov/power/data/fist_pub.html

Download or view item 3-3 "Electrical Connections" You will see:

"7.1. CURRENT AND TEMPERATURE LIMITATIONS.- The amount of heat generated in a conductor is proportional to its resistance and to the square of the current it carries, while the temperature rise depends on the rate at which the heat is dissipated through convection, radiation, and conduction.
7.1.1. Current-carrying capacity of a bus.- The current-carrying capacity of a bus is limited by the temperature rise produced by the current and other factors. Buses for generating stations and substations are generally rated on the basis of the temperature rise which can be permitted without danger of overheating equip-merit terminals, bus connections, and joints. ANSI C37.20C-1974 (IEEE standard 27-1974) permits a hottest spot temperature rise for plain
copper buses of 30 EC (54 EF) above an ambient temperature of 40 EC (104 EF), The standard allows a hot spot temper-attire rise of 65 EC (117 EF) for metal-en-closed applications where silver contact surfaces are used on connections and a hot-spot temperature rise of 45 EC (81 EF) for silversurfaces terminals of outgoing circuits."

These generally apply to permanent connections, not separable contacts. But I think the material limitations are similar.

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