A normal, open electrical contact pair, mounted in a small relay, was used to make and break repeatedly a dc, 3OV13 P resistive circuit up to 100 thousand times; and the relationship between data for each switching and switching interval are analyzed in this paper. Four kinds of switching intervals are set by changing the frequency of applying the rated voltage to drive the electromagnetic coil.No special relationship was found between four differeat switching operation intervals and data for bounce number at make, arc duration at m a k e l b d , and contact resistance at 500 ms after the 10-A current began to flow.On the other hand, the following points became clear through the experiments.-Temperature at the backside of contacts at 500 ms after the 10-A current began to flow changes drastically by the difference of the switching interval.-Temperature rise changed linearly and was proportional to the contact resistance at each switching interval.-The more frequent the switching interval, the larger the proportional coefficient.By these results of experiments, the following facts were concluded.-Temperature of electric contact increases with Joule heating of contact resistance and the resistance of the conductor including supporting arms.-The shorter the period of the separated contacts, the larger the temperature difference between measuring point and room temperature became.

While the AgPd40/60 electrical contacts mounted on the miniature relays continued to make and break a dc 30 V‐10 A resistive circuit for 100,000 times, on every switching operation the number of bounce, the duration of closing are, the contact resistance, the temperature on the stationary contact arm, and the duration of opening are were measured and recorded. In this paper, these measured values are shown in many figures and compared with data on Ag, Pd, AgCdO12 wt percent and AgSn2 9.3 wt percent. Furthermore, the values measured on some switching operations before and after the contact pairs adhered are listed in the tables. The variation of the closing are duration has the same tendency as the increase and decrease of the number of contact bounce. Also, the contact resistance becomes low after the closing operation in which the duration of the closing are is long. However, the average duration of the closing are was about half that in Pd pairs and was the same degree in Ag and AgSn2 9.3 wt percent contacts. Although the duration of the opening are was double that in Pd contacts, it was not especially long compared with that in Ag, AgCd0 12 wt percent and AgSnO2 9.3 wt percent contacts. However, the pip made of transferred metal on the anode surface would grow largely rather than be scattered by subsequent switching arcs. This largely grown pip causes contact sticking, as in the case of Pd contacts. Although black polymer is observed on two contact surfaces, the top of a large pip on the anode and the bottom of an eroded crater on the cathode are whitish metallic surfaces with microroughness. Thus, the contact resistance at current of dc 10 A was unchanged for 100,000 switching operations. However, the average contact resistance was higher than that of Ag and Pd contacts measured under the same experimental condition.

To a relay with supporting arms in which only the tips with electrical contacts are parallel, AgCdO electrical contacts with Au flash are installed as a normally open contact pair. Within the circuit with dc 30 V ‐ 10 A and a resistive load, it is used as the make‐only, the break‐only, and the make‐and‐break contact pair. the electrical characteristics at each make and break and the contact surface damage after 100 thousand operations were measured. In the sample electrical contact pair with the tips of supporting arms in parallel, it is demonstrated by experiments that arc damages (roughness and black and brown contaminant) occur at the center of the contact surface. The arc trace at the make‐only electrical contact is the narrowest in comparison with two other switching operations and is a milky metallic color surface with many infinitesimal irregularities. In the case of the break‐only and make‐and‐break contacts, large irregularities exist at the center of one of the electrode surfaces. A thick black and brown contaminant exists in this part and surroundings. Also, contact sticking occurred in all samples of make‐only contacts but not in the break‐only contacts. The black and brown contaminant between the contact surfaces prevents locking and increases the contact resistance and the variation width so that they cause a longer duration in the breaking arc.