This arrangement normally maintains a 50 volt negative battery on the alarm extension wire (the other wire of the pair is used to extend clock pulses from Norchard to Parkend). This battery holds relay NB at Norchard operated and the green "normal" lamp lit on the U13 C unit alarm panel.

Should a prompt alarm occur at Parkend, or the cable pair go "dis", then the negative battery is removed and NB releases to dim the green "normal" lamp and light the red "prompt alarm" lamp.

If a deferred alarm occurs then the negative battery is replaced with a positive battery and relay PB operates in place of NB and this lights the white "deferred alarm" lamp at Norchard.

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Page provided by John Bathgate This page was last updated on 13th December 2010