No, it is not, but it is warmly suggested. The relays are studied to stay firmly on the sockets without the clip in standard conditions, however, the clips guarantee a perfect stay in place even in case of heavy shock or vibrations. Consider not only the destination of the machinery or panel that could be without mechanical stress but also the transportation. The transportation on the installation place can be cause of heavy shock and vibration and the clips avoid any problem of relay
dropping.

____________________________________________

Other information on this topic

Make sure to visit the General purpose relays website page.

Take a look to the brochure.