What This Article Covers
A fail safe electrified mortise lock with a double cylinder deadbolt is a more layered opening than most contractors expect on first encounter. The electrical behavior at power loss, the key schedule for both cylinders, and the egress compliance review all have to be resolved in a specific order — and the wiring sequence has to be locked in before anyone picks up the key bitting sheets. This guide is written for commercial hardware contractors, security consultants, and facility managers who are coordinating the access control package with the physical keying program on the same opening.
What a Fail Safe Double Cylinder Mortise Lock Actually Does
Start with the function, because the language gets misread on submittals. A fail safe electrified mortise lock is energized to lock and releases — unlocks — when power is removed. On an opening where the outside lever is locked and the lock body carries a double cylinder deadbolt, that means:
- Under normal powered conditions, the outside lever is held locked by the electric solenoid.
- The deadbolt requires a key turn from either side to throw or retract it — there is no thumbturn on the inside.
- On a power loss event, the solenoid releases and the outside lever returns to free passage, but the deadbolt does not automatically retract — it stays wherever it was last set mechanically.
That last point is where projects go sideways. Designers sometimes treat fail safe as a full open-on-power-loss guarantee. It is not, if the deadbolt is thrown. The deadbolt remains in the position it was keyed to last, regardless of electrical state.
Why Wiring Mode Has to Be Decided First
Before a key schedule is written, the project team needs to answer one question: what is supposed to happen at this opening when power fails? The answer drives every downstream decision.
Scenario 1 — Power Failure Should Allow Free Egress
If the requirement is that the door opens freely on power loss — say, a secured corridor in an office building covered by IBC egress rules — then the wiring mode is fail safe on the lever function. In this scenario the key schedule for the inside deadbolt cylinder should be limited to authorized personnel only, because an improperly thrown deadbolt at shift change will counteract the fail safe behavior during an outage. The hardware and key control decisions are directly linked.
Scenario 2 — Power Failure Must Not Open the Door
This is fail secure territory, and a double cylinder deadbolt paired with fail secure is a common combination on pharmacy storage, evidence rooms, or server corridors in healthcare or institutional settings. If that is the actual requirement, then fail safe is the wrong function specification to begin with — and the submittal needs to be flagged before installation, not after commissioning. Catching this during the hardware schedule review saves significant rework cost.
Scenario 3 — Fire Alarm Release Is in the Sequence
Many electrified openings are wired to the fire alarm control panel so the lock releases on alarm. On a fail safe mortise lock, this is straightforward for the lever — power drops, lever frees. But if the deadbolt is thrown on a fire alarm event, occupants still need a key to retract it. Specifiers writing these openings for life safety corridors in healthcare or educational facilities need to verify with the authority having jurisdiction whether a double cylinder deadbolt is acceptable at that location, or whether a thumbturn (single cylinder) configuration is required instead. NFPA 101 and IBC both carry egress provisions that affect this call.
The Key Schedule Coordination Problem
A double cylinder deadbolt opening has two cylinders — inside and outside — that may or may not be keyed alike, and may or may not be keyed into the master key system at the same level. Here is where the wiring-first principle matters practically:
- If the inside cylinder is on the grand master, maintenance and security staff can throw or retract the deadbolt from either side. That sounds convenient until a night-shift employee deadbolts the door at 2 a.m. and power fails at 6 a.m. The lever releases; the bolt does not. The opening appears locked out.
- If the inside cylinder is restricted to a limited key, fewer people can inadvertently leave the deadbolt thrown. But then someone has to audit that the deadbolt is retracted at the end of each controlled period — which requires a procedure, not just a key.
- Construction keying on a double cylinder opening means both cylinders are on the construction master during the build phase. The sequence for removing construction cores and installing permanent cylinders should be coordinated with the access control system commissioning, so the electrical function is tested with the correct hardware in place.
Power Transfer: Getting Voltage to the Lock Body
Electrified mortise locks require a continuous low-voltage power path from the power supply through the frame, across the hinge line, and into the lock body. On doors from ASSA ABLOY group companies — including Accentra (formerly Yale) — pre-wired doors are available with ElectroLynx connector harnesses built in, which eliminates the need to drill for field wiring and keeps fire ratings intact. On doors without that prep, a retrofit harness paired with an electrified transfer hinge is the standard solution.
Wire gauge selection depends on total run length and current draw. Accentra EcoFlex electrified mortise locks operate on 12 or 24 VDC and are polarity sensitive — verify polarity at the connector before applying power. Operating voltage must stay within plus or minus 10 percent of nominal. Longer wire runs require heavier gauge to avoid voltage drop that causes inconsistent solenoid behavior. Consult the wire gauge chart in the installation instructions and coordinate with the Division 26 electrical contractor early — this is not a last-day connection.
Egress Compliance Review Points
Before finalizing a double cylinder fail safe mortise lock on any opening, run through these compliance checkpoints:
- Is this opening on a required egress path? IBC and NFPA 101 restrict double cylinder deadbolts on certain egress doors. Verify with the authority having jurisdiction.
- Does the fail safe release satisfy the occupancy requirement? Lever-free egress on power loss may not be sufficient if the deadbolt can be thrown by anyone holding an inside key.
- Is panic hardware required? If the occupancy load or occupancy classification triggers a panic hardware requirement, an electrified mortise lock — regardless of fail safe mode — is not a direct substitute without additional review.
- Fire alarm interface? Confirm with the fire alarm contractor that the release wiring method — whether through the access control panel or directly to the FACP — is consistent with the local code edition adopted.
Specifying the Right Lock from the Start
Accentra 8800 Series electrified mortise locks, available through DoorwaysPlus, offer the function combinations — including fail safe with double cylinder deadbolt and outside lever locked — that match these demanding opening types. Corbin Russwin and Sargent also carry electrified mortise product lines suited to the same applications. The right choice depends on keying system compatibility with other hardware already on the project, finish matching requirements, and the trim style called out in the schedule.
DoorwaysPlus can assist with product selection, comparable alternatives across preferred lines, and coordination of electrified opening packages. Contact us before the hardware schedule is finalized — not after the door is prepped.