I have been asked how to power the locks for a fail safe/fail secure door using the PP8FR.
Fail safe/secure doors use two electric locks, one to release on fire or emergency and one to stay locked to maintain access control back into the building.
Often this is achieved by controlling the negative/ ground connection via the access control relay. The ground connection is fed from the power supply to the relay common and then the N/C and N/O relay contacts are fed, one to each lock so that when a card is presented the fail safe lock looses power and the fail secure lock turns on allowing access.
The problem comes when you need to fire trip the fail safe lock. The fail secure lock can’t be fire tripped as it will stop working. This is solved by breaking only the positive power feed to the fail safe lock. This can be easily done using separate fused outputs from the PP8FR. See diagram below.
The actual relay contacts used will vary depending on how the manufacturer labels their outputs. This method also has an added advantage, if one of the locks is tampered with and/or goes short circuit then only one fuse will blow leaving the other lock still functioning and keeping the door secure.