The Model 571B consists of 2 double-pole, double throw relays, and 1 four-pole, double throw relay. The FormC contacts allow switching between circuits. Typical applications would be paging override of background music in zone paging systems, or switching talkback circuits for two-way communications. The relays are sealed to prevent contamination in difficult environments. All of the relays, on both models, are activated by applying ground to the appropriate control pin. By offering different models, the system designer can choose a unit that will fit the application perfectly. This will result in a more cost effective design. Also, the relay switching modules can be mixed and matched with other INTEGRA III SYSTEM cards, such as solid-state switchers, mixers and remote controls, within the same card frame.