Significant increase of the dielectric performance of plastic sealed telecom relays

Initialised by Bellcore the dielectric requirements on telecom relays were significantly increased in the last years. In parallel the dimensions of the relays had to become smaller and smaller in order to safe space on printed circuit boards in electronic equipment. By filling plastic sealed relays with the electro-negative gas sulfurhexafluoride (SF/sub 6/), the dielectric withstand voltage of the relays was increased by a factor 2 compared to that with a normal gasfilling with nitrogen. This method allows to guarantee a withstand voltage of more than 3500 V between coil and contacts and more than 2500 V between open contacts without increasing distances in the design of the relay. The consequence of an SF/sub 6/-filling on the life endurance of a relay was investigated extensively. The results show that no significant difference to relays with an N/sub 2/-filling exists in this respect. The gas tightness of the relay housing is sufficient to guarantee an SF/sub 6/ loss of less than 10% during a lifetime of more than 25 years even under severe climatic conditions.