The fuse card consists of 6 double fuses, one at each plus and minus. Each fuse has a circuit that senses if the fuse is intact or broken. A blown fuse is indicated by a red light emitting diode (LED). The card has an output relay NC for signalling fuse-failure. To easily test if a fuse is intact or broken there is an open fuse holder in the middle of the card where a fuse can be installed and tested. Is the fuse OK it is indicated by a green LED. To ensure that no ground currents disturb the installation, the fuse card has a ground failure circuit which detects if any of the polarities accidentally is connected to the
protective earth (PE). Especially, this is important in large installations. An earth fault leads to creep currents in the earth that can interfere with detectors and control panel sections and give false alarms. The ground failure circuit detects whether there is a current of a certain size between terminal (+) or (-) and ground (PE). The sensitivity of each pole is set by a potentiometer on the board. A ground fault is indicated by a red LED for each pole and an output relay NC is signalling ground faults. Potentiometer turned most left will disable ground fault monitor for given channel. Enabled channel PE ground fault monitor is signalled by short blinks of LEDs GF+ and GF-. There is also a circuit which lights a green LED when voltage input to the board is present.