The PNOZ s7 is used to increase the number of instantaneous safety contacts available on a base unit. Base units are all safety relays with feedback loop monitoring. The max. achievable safety level depends on the base unit. The contact expander module expands an existing circuit. As the output relays are monitored via the base unit’s feedback loop, the safety functions on the existing circuit are transferred to the contact expander module. The safety function remains effective in the case of a component failure.