[MEP Center Engineering]

Starter question — a frequently asked question posted by the MEP Center team to open this forum. Share your own experience below.

An office building uses card readers on doors that are also on escape routes: stair doors, corridor doors and the main exit. The security consultant prefers fail-secure electric strikes so that doors stay locked during a power cut.

• Which locking mode is acceptable on an escape door?
• How must the lock interface with the fire alarm, power loss and a manual release?
• How do I size the lock power supply and its battery?

[MEP Center Engineering]

Doors on an escape route must let people out at all times. Either the free-egress side has mechanical hardware that always opens (lever, EN 179 emergency exit device, EN 1125 panic bar), or an electrically held lock must be fail-safe and release on fire alarm, on loss of power and from a manual release device. A fail-secure lock without mechanical free egress is not acceptable on an escape door.

Two acceptable arrangements

1. Fail-secure strike or motor lock, with mechanical free egress. The lock controls entry only. From the escape side the door always opens with one action on the lever or panic hardware. Security is kept during power loss and egress is never affected. This is often the best option.
2. Fail-safe lock (magnetic lock or fail-safe strike) that locks the egress side as well. Then you need release on fire alarm activation, on power loss, and from a manual release (break-glass or push button) next to the door. In Europe EN 13637 covers electrically controlled exit systems. In the US, NFPA 101 (7.2.1.6) covers delayed-egress and sensor-release locks, typically with a release device mounted 1 015 to 1 220 mm (40 to 48 in) above the floor and within 1 525 mm (60 in) of the door. Delayed egress is limited to 15 s, or 30 s where the authority approves.

Wiring principles

• The fire alarm release must remove power from the lock directly, downstream of the power supply and its battery. A software command through the access controller is not enough.
• The manual release must act on the lock circuit by hardware, without depending on the controller.
• Release should be by zone, as set out in the cause and effect matrix. See How to Write a Fire Alarm Cause and Effect Matrix.

Worked example: power supply and battery

Six 24 V DC magnetic locks at 0.25 A each, plus the controller and readers at 0.5 A.

1. Load: 6 × 0.25 + 0.5 = 2.0 A. Choose a PSU of at least 2.5 A plus the battery charging current.
2. Security autonomy required: 4 h. Capacity: 2.0 × 4 = 8 Ah. Divide by 0.8 for ageing: 10 Ah.
3. Choose two 12 V 12 Ah batteries in series for 24 V.

The battery keeps doors secured during a mains failure. A fire alarm still drops the locks, because the release relay sits after the battery. If the client prefers doors to release on mains failure, no battery is needed for the locks, but say so in the specification.

Common mistakes

• Magnetic locks on escape doors with no manual release.
• Fire alarm release wired to the controller input only.
• Stair doors used by firefighters left locked on the stair side without a defined re-entry policy.
• No test of the release in the commissioning procedure.

Emergency lighting at these doors: Emergency Lighting: Quick Design Rules.

For deeper study: MEP Center online certified courses.

Check the edition of the code that applies to your project.

[Author]

Posts