Why the Wiring Plan Comes Before the Hardware Order
This article is for commercial contractors, low-voltage integrators, and specifiers who are adding a fail secure electrified mortise lockset to a project and need to understand the decisions that must be made before the door goes in the frame. Getting the power method, voltage, wire gauge, and egress-code position settled at the design stage prevents costly field corrections and keeps the authority having jurisdiction (AHJ) happy at inspection.
What Is a Fail Secure Electrified Mortise Lock?
A fail secure electrified mortise lockset is energized to unlock and de-energized to lock. In plain terms: when power is removed — whether by a normal access-control release, a fire-alarm signal, or an unplanned outage — the outside lever stays locked. The latchbolt still retracts freely from the inside, preserving egress. This is the opposite of a fail safe lock, which unlocks when power is lost.
Common applications include server rooms, pharmacy dispensing areas, restricted corridors in healthcare, electrical and mechanical rooms in schools, and any tenant space where security must be maintained during a power interruption. The function is also used in retail back-of-house and industrial facilities where after-hours access control is the primary concern.
Code Position: Where Fail Secure Is Permitted
This is the decision that trips up the most projects. Fail secure is not universally permitted on every opening.
- Egress doors on required means of egress must always allow free egress from the inside regardless of power status. A fail secure mortise lock satisfies this because the inside lever or thumbturn retracts the latch mechanically — the electrical function only controls the outside lever.
- Panic hardware requirement: Where an occupancy load or occupancy type requires listed panic hardware, an electrified mortise lock cannot substitute for that requirement. Verify occupancy and load with the AHJ before specifying.
- Fail secure mode on an electrified lock shall not interfere with the operation of listed panic hardware on the same opening, per standard installation guidance for electrified mortise products.
- Wiring methods must comply with ANSI/NFPA 70 (National Electrical Code) and any local amendments. Low-voltage wiring in plenum spaces requires appropriately rated cable.
If you are unsure whether fail secure is the correct mode for a specific door, review the door's egress category and consult the AHJ before the hardware ships.
Power Transfer: Getting Voltage to the Lock Body
An electrified mortise lock needs a continuous low-voltage power feed from the access-control panel or power supply through the frame and across the door. There are three common methods:
- Electrified hinge with plug-in connector system — The cleanest solution. A transfer hinge carries conductors through the hinge knuckle; a standardized connector snaps to the lock's pigtail inside the door. No visible wiring on the door face, fire-rating is maintained, and future hardware changes are simplified. ASSA ABLOY Group companies ship many doors pre-wired with ElectroLynx connectors for exactly this setup.
- Door cord (loop) — A flexible armored or jacketed loop at the top of the door carries wiring from frame to door. Visible but reliable. Common on retrofit projects where the door and frame are already in place and rewiring the hinge position is impractical.
- Hard-wire through the door edge — Used on non-connector doors without a transfer hinge. Requires drilling a wiring channel through the door, routing conductors carefully, and making field splices with proper crimp connectors or wire nuts per local code. More labor-intensive and leaves no plug-and-play upgrade path.
If the door is not pre-wired, a retrofit harness paired with an electrified hinge is often the fastest path to a clean, code-compliant installation. Talk to your hardware distributor about which transfer solution is stocked or available to ship with the lock body.
Voltage and Wire Gauge: Settle This on Paper, Not at the Panel
Most commercial electrified mortise locks in this category accept a dual-voltage input — typically 12VDC or 24VDC continuous. The operating voltage must not vary more than plus or minus 10 percent from nominal, so voltage drop over the wire run is a real design concern, not a footnote.
Wire Gauge by Run Length
At 24VDC with a 0.5A design load, a general guide from manufacturer installation documentation shows:
- Up to 100 ft one-way run: 20 AWG acceptable
- 100 to 150 ft: 18 AWG
- 150 to 200 ft: 18 AWG at 24V (drop to 14 AWG at 12V for the same run)
- 200 to 250 ft: 16 AWG at 24V
- Minimum permissible wire size: 26 AWG — but real-world runs rarely justify going that small
Always calculate the full one-way wire run from the power supply to the lock, not just the distance from the nearest panel. Long conduit runs through mechanical spaces add up quickly.
Note that the lock body is polarity sensitive on hard-wired installations. Label conductors clearly at both ends before pulling wire — reversing polarity at termination is a common cause of lock-does-not-release calls after installation.
Monitor Switch: Plan the Feedback Loop Early
Many electrified mortise locks include an integrated monitor switch that reports door or bolt position back to the access-control panel. The switch rating on these units is typically 2A maximum at 30VDC. If your access-control system needs door-position status, confirm the monitor switch output matches the panel input before the order is placed — adding a separate door position switch later means more drilling and more wiring.
The Door Prep Conversation No One Has Early Enough
An electrified mortise lock uses the same ANSI/BHMA standard mortise prep as its mechanical counterpart, but the trim package has one additional requirement: a wiring passage from the lock body to wherever the pigtail exits the door edge or stile. On hollow metal doors this is straightforward. On solid-core wood doors, the wiring channel must be planned before the door ships from the mill — adding it in the field risks splitting the stile or voiding the fire label if the door is rated.
Confirm with the door manufacturer or millwork supplier that the door is specified for electrified hardware before it leaves the factory. If you are working a retrofit on an existing wood door, consult a qualified installer before drilling.
Preferred Hardware Lines for Electrified Mortise Applications
When specifying an electrified mortise lockset for a controlled opening, DoorwaysPlus stocks product from lines known for stable platform designs and service-friendly part availability — including Accentra (formerly Yale Security), Corbin Russwin, and Sargent. These lines share common ANSI prep dimensions, so a project hardware set can stay consistent across mechanical and electrified openings without mixing body formats.
If your project schedule is tight, note that electrified mortise locks typically carry a lead time of two to four weeks — coordinate the order early so the lock arrives before the frame is set and the low-voltage rough-in is closed up.
Quick Pre-Order Checklist for Fail Secure Electrified Mortise Locks
- Confirm fail secure mode is permitted by the AHJ for this specific door function and occupancy
- Verify the door is prepped or will be prepped for electrified hardware (wiring passage, connector system)
- Select power transfer method: electrified hinge with connector, door cord, or hard-wire
- Choose supply voltage (12V or 24V) and confirm power supply capacity — note max two locks per 1A supply at peak draw
- Calculate one-way wire run length and select appropriate AWG
- Confirm polarity labeling convention with the low-voltage installer before wire pull
- Verify monitor switch output matches access-control panel input if door position reporting is required
- Check lead time against the project schedule and order early