Dimensioning a contact with respect to its heating

Abstract

The underwriters’ rules for dimensioning electric line contacts are usually founded on the principle that the R I ² heat must not raise the temperature of the contact beyond a certain limit. Fixing this limit is a problem in itself. From § 31 we see that stationary contacts can endure 100 to 150 °C for a long time if they are good from the beginning. In practice the temperature limit is usually lowered to gain greater security for the case that the connection by means of the contact is made less accurately, as well as for other reasons. We shall discuss the suitable temperature limit at the end of this chapter, and now only remark that it would be possible to increase the temperature limits which are prescribed nowadays if said connections were made with greater care.