Mag Lock on a Fire-Rated Egress Door
A Newark, Delaware, medical office has a single required egress door from a treatment corridor. The door is a 20-minute fire-rated assembly with a closer and positive latching hardware, but the contractor installed a 1,200 lb electromagnetic lock controlled by a card reader on the outside and a push-to-exit button inside. The push button releases the lock; there is no door position sensor, no connection to the fire alarm panel, and no manual key override. The lock is powered by a 12 VDC 500 mA supply through 180 ft of 18/2 cable. At the lock, measured voltage is 11.1 V; the lock minimum is 10.8 V, and it has dropped out intermittently when the HVAC compressor starts. The local AHJ has scheduled a life-safety inspection. The owner wants to keep the mag lock because it provides an audit trail.
1. Identify the life-safety deficiencies and determine whether the mag lock can remain.
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A mag lock is not automatically prohibited on a required egress door, but it must comply with the access-controlled egress door provisions of the adopted life-safety code. As installed, the door lacks an approach sensor on the egress side and a release connection to the fire alarm system. The push button may serve as a manual release, but it is not a substitute for the other required features. Because the door is a 20-minute fire-rated assembly, the lock arrangement must also preserve positive latching and be listed for fire-door use. The intermittent dropout and the lack of fire alarm release are unacceptable. The owner can keep the audit trail by using a compliant access control system, but the mag lock must be tied to the fire alarm, provided with an egress sensor, and coordinated with the fire-rated door hardware.
2. Calculate the voltage drop on the 180 ft 18/2 circuit and recommend a power remedy.
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18 AWG copper is about 6.4 ohms per 1,000 ft. The loop is 360 ft, so R = 6.4 x 0.360 = 2.30 ohms. At 0.5 A, drop = 1.15 V. A 12.25 V supply would produce 11.10 V at the lock, which matches the measurement and leaves only 0.3 V above the 10.8 V minimum. HVAC compressor startup may also be pulling down the supply or a shared circuit. Use 16 AWG or 14 AWG for margin: 16 AWG loop R is about 1.45 ohms, drop 0.72 V; 14 AWG loop R is about 0.91 ohms, drop 0.46 V. I would also use a dedicated, filtered 12 VDC power supply with battery backup on the lock circuit, not a supply shared with HVAC equipment. Verify voltage at the lock during worst-case building load.
3. Describe the correct sequence of operation for the access-controlled door.
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Normal access: a valid card read releases the lock for the programmed time. Egress: an approach sensor detects a person moving toward the door and releases the lock, and the inside manual release button also releases it. Fire: activation of the fire alarm system must release the lock through a monitored relay or listed interface. Power loss: the lock must fail safe and release. The door must have a closer and positive latching hardware suitable for the fire-rated assembly. Provide signage as required by the AHJ, and do not rely on the card reader or the audit trail as a substitute for free egress. Test the sensor, push button, fire alarm release, and power-loss release during the inspection.