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newSchoolWorks.com › VoTechWorks › Business & Cross-Cutting › Locksmith & Security Systems › Access Control Systems: Installation, Programming, and Service › Lesson 3
BUS-LOCK72-05 · Lesson 3 · 14 clock hours · lab

Hardware Installation: Readers, Electric Locks, and Door Position Devices

Objective. Students will mount and align a proximity card reader, an electric strike and a magnetic lock at a practice door station, wire each device to a controller, and verify correct mechanical operation of the door hardware before powering the system.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a credentialed professional in the field or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

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Hardware Installation: Readers, Electric Locks, and Door Position Devices

Access control works only when the physical hardware is installed correctly. A credential reader that is wired backward, a magnetic lock with a misaligned armature, or a door position switch mounted on the wrong surface can each defeat the entire system. This lesson teaches you to mount, wire, and verify three core devices — a proximity card reader, an electric strike or magnetic lock, and a door position switch — before any power is applied.

Safety First

Before you pick up a drill, put on safety glasses and cut-resistant gloves. These stay on throughout all drilling, panel work, and wire-termination tasks. When working near door frames and hinges, keep fingers clear of pinch points. If the practice door is connected to any live circuit from a previous exercise, verify the controller is de-energized and the power supply is unplugged before touching terminals. Label the power supply with a caution tag so no one else energizes it while you are working — this is the lockout/tagout principle applied to low-voltage systems. Low-voltage does not mean zero risk: a short across a 12 V, high-current power supply can produce a damaging arc and damage components.

Reader Mounting Height and Placement

Proximity card readers must be usable by all people, including wheelchair users. ANSI/BHMA accessibility guidelines place the credential-presentation area of a reader at approximately 34 to 48 inches above the finished floor (AFF). The practical target most installers use is 42 inches AFF to the center of the reader face, which falls comfortably within that range and matches the height used for door hardware under accessibility standards.

Use the manufacturer's mounting template — every commercial reader ships with one. Tape it to the wall or door jamb, confirm the center height with a tape measure, mark hole locations with a pencil, and then use an awl or a small drill bit to start pilot holes. On hollow-core practice panels, a standard drywall bit works; on metal backboxes, use a metal-rated bit and cutting fluid. Drive all fasteners firmly but do not overtighten; a torque screwdriver set to the value in the installation sheet prevents cracking the reader housing. Route the reader's pigtail cable or conduit stub through the knockout before seating the reader.

Electric Strikes

An electric strike replaces the fixed strike plate in a door frame. When the strike is energized (or de-energized, depending on fail mode), its keeper pivots to allow a latch bolt or deadlatch to pass. Installing one requires that the strike body fits the cutout in the frame — ANSI-standard cutouts have defined dimensions so most strikes are interchangeable with the correct faceplate. After seating the strike body, check the door gap with a feeler gauge; the gap between the door edge and the frame face should match the manufacturer's specification, typically 1/8 inch or the value stamped on the frame. Too large a gap prevents the latch from seating; too small a gap causes binding.

Electric strikes can be wired fail-safe (power to lock, loss of power = unlocked) or fail-secure (power to unlock, loss of power = locked). Life-safety codes generally require egress doors to be fail-safe so occupants can exit during a power failure. Confirm the fail mode requirement with local building and fire codes before wiring.

Magnetic Locks

A magnetic lock (magloc) mounts on the door header and holds a steel armature plate attached to the door. When energized, the electromagnet develops holding force — commonly rated at 600 lb for single-door applications. Unlike an electric strike, a magloc has no moving parts, which makes it reliable but also means there is no mechanical backup: if power is lost the door opens. This means all maglocs are inherently fail-safe.

Proper armature alignment is critical. Mount the magloc body to the header bracket first, then close the door and allow the armature to self-center against the magnet face. Tighten the armature mounting screws with the armature held flush — misalignment reduces holding force dramatically and can cause nuisance releases. After alignment, verify there is no gap between the magnet face and the armature face when the door is closed; even a 1/32-inch gap can cut holding force by more than half.

Request-to-Exit (REX) Devices and Door Position Switches

A Request-to-Exit (REX) device lets someone leave the secured side without presenting a credential, preventing the lock from registering an alarm when the door opens legitimately from inside. Passive infrared (PIR) REX sensors detect motion on the egress side and signal the controller to release the lock; push-button REX devices do the same with a manual press. Mount PIR REX sensors so the detection zone covers the entire door swing area and does not extend to the public side.

A door position switch (DPS) tells the controller whether the door is physically open or closed, independent of lock state. Surface-mount reed switches are the most common type: one half mounts on the frame, the magnet half mounts on the door, aligned within the gap tolerance stated by the manufacturer (typically 1/2 inch or less). Wire the DPS to the normally-closed (NC) input on the controller; an open door breaks the circuit and the controller logs a door-open event.

Pre-Power Checklist

Never energize a new installation without completing a structured pre-power checklist. Verify every wire termination is seated and the correct polarity is observed for polarized devices. Confirm door gap measurement is within specification. Check that the armature seats flush on the magloc. Verify REX wiring is connected to the correct controller input. Manually operate the latch or armature to confirm free movement (free-wheeling test). Your instructor must sign the checklist before you plug in the power supply. After energizing, test all four functions: valid credential releases lock, invalid credential is denied, REX releases lock from inside, and DPS shows correct state in software.

Key terms9

Fail-safeA lock wiring mode in which the device is locked when power is present and unlocks when power is lost, ensuring free egress during a power failure.
Fail-secureA lock wiring mode in which the device remains locked when power is lost, used where security takes priority over free egress (not permitted on life-safety exit paths without additional hardware).
Electric strikeA frame-mounted device that replaces a fixed strike plate; its pivoting keeper allows a door latch to release under electrical control.
Magnetic lock (magloc)An electromagnetic lock consisting of a magnet body mounted to the door header and a steel armature plate on the door; it holds the door closed by magnetic force when energized.
Armature plateThe steel plate mounted on the door that contacts and is held by the magnetic lock body; correct alignment with the magnet face is essential for rated holding force.
Request-to-Exit (REX)A device — passive infrared sensor or push button — that signals the access control controller to release the lock when a person on the secured side wants to exit without presenting a credential.
Door position switch (DPS)A reed switch assembly that reports the physical open or closed state of the door to the access control controller, independent of lock energization.
AFF (above finished floor)The standard measurement reference for mounting heights of hardware and devices, measured vertically from the floor surface to the specified point on the device.
Feeler gaugeA set of precision metal blades of known thickness used to measure small gaps, such as the gap between a door edge and the door frame when fitting an electric strike.

Worked examples4

1. You are mounting a proximity card reader. The manufacturer states the credential-presentation center must be at 42 inches AFF. The mounting template shows the center of the template is 2 inches above the center of the credential-presentation zone. At what height above the floor should you tape the top reference mark of the template?
  1. Identify the target AFF for the credential-presentation center: 42 inches.
  2. Identify the offset from the template top reference mark to the credential-presentation center: 2 inches above the center means the reference mark is 2 inches higher.
  3. Add the offset to the target AFF: 42 inches + 2 inches = 44 inches.
  4. Tape the top reference mark of the template at 44 inches AFF.
Answer: The top reference mark of the template should be placed at 44 inches AFF, so that the credential-presentation center of the mounted reader sits at exactly 42 inches AFF.
2. After installing an electric strike, you measure the door gap with a feeler gauge. The manufacturer specifies a door gap of 1/8 inch (0.125 inch). Your feeler gauge reads 0.094 inch (3/32 inch). Is the gap within specification, and what is the difference from the target?
  1. Convert all measurements to the same unit (decimal inches): target = 0.125 inch; measured = 0.094 inch.
  2. Calculate the difference: 0.125 − 0.094 = 0.031 inch.
  3. Compare to specification: 0.094 inch is less than 0.125 inch, so the gap is too small.
  4. Determine the action needed: the door or strike position must be adjusted to open the gap by approximately 0.031 inch to reach the target.
Answer: The measured gap of 0.094 inch is 0.031 inch below the specified 0.125 inch. The gap is too small; binding may occur and the strike may not operate correctly. The installation must be adjusted before the system is energized.
3. A magnetic lock is rated at 600 lb holding force when the armature is perfectly flush. A technician leaves a gap of approximately 1/16 inch between the armature and the magnet face. If a gap causes holding force to drop by roughly 50% for every 1/32 inch of gap (a simplified rule of thumb), estimate the remaining holding force.
  1. Identify the gap: 1/16 inch = 2/32 inch = 2 increments of 1/32 inch.
  2. Apply the rule of thumb: first 1/32 inch reduces force by 50%: 600 × 0.50 = 300 lb.
  3. Apply the second 1/32 inch reduction: 300 × 0.50 = 150 lb.
  4. State the estimated remaining holding force: approximately 150 lb.
Answer: With a 1/16-inch gap, the estimated holding force drops to approximately 150 lb — only 25% of the rated 600 lb. This demonstrates why flush armature alignment is critical and why gaps must be eliminated before the system is placed in service.
4. A door position switch has a maximum gap specification of 1/2 inch (0.5 inch) between the magnet half and the switch half. After mounting, you measure the gap as 9/16 inch. Is this within specification, and by how much does it exceed the limit?
  1. Convert 9/16 inch to a decimal: 9 ÷ 16 = 0.5625 inch.
  2. Compare to the specification limit: 0.5625 inch vs. 0.5000 inch.
  3. Calculate the excess: 0.5625 − 0.5000 = 0.0625 inch (or 1/16 inch).
  4. Determine compliance: the gap exceeds the specification by 1/16 inch; the switch may not reliably detect the closed-door state.
Answer: The 9/16-inch gap exceeds the 1/2-inch specification by 1/16 inch. The door position switch must be repositioned closer to its magnet half to fall within the manufacturer's gap tolerance before the installation is accepted.

The math in this lesson1

Learners add a 2-inch template offset to a 42-inch target to mark 44 inches above finished floor.
7.EE.3
Brush up in the math halls at newSchoolWorks.com:
In class: Hands-on mounting exercise: each student selects an installation instruction sheet for a specific reader model, locates the mounting height per ANSI/BHMA accessibility guidelines (approximately 34–48 inches AFF for the credential presentation area), marks the mounting template, drills or uses an awl for hollow-core practice panels, and mounts the reader with all fasteners torqued appropriately. · Electric strike and magloc comparison lab: students install one electric strike in a hollow-metal door strike pocket (adjusting strike lip depth and checking door gap with a feeler gauge) and then install a magnetic lock on a door header including the armature plate alignment; both devices are wired to fail-safe and fail-secure switch positions on the practice controller so students observe the operational difference. · Pre-power checklist drill: before any power is applied, each student completes a written pre-power checklist covering wire termination check, door alignment and gap measurement, maglock bond strength estimation, REX device placement and wiring, and lock free-wheeling test; instructor signs off the checklist, then students energize and verify lock engage/release with a credential swipe.
Materials: Proximity card readers (HID or equivalent), electric strike (ANSI-standard cutout), magnetic lock (600 lb or similar), door position switch (surface-mount), REX passive infrared or push-button, practice door frame assembly (hollow-metal or wood), drill and bits, hole saw, screwdrivers, Allen wrenches, feeler gauge, torque screwdriver, pre-power checklist form, ANSI/BHMA door hardware standards reference, manufacturer installation sheets, PPE (safety glasses, cut-resistant gloves)
Check: Completed pre-power checklist must be signed by instructor before energizing; after power-on, instructor observes student demonstrate: valid credential grants access (lock releases), invalid credential is denied, REX releases lock from inside, door position switch shows correct open/closed state in controller software — all four functions must pass for lesson credit.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Access Control Installation
1. According to ANSI/BHMA accessibility guidelines, the credential-presentation area of a card reader should be mounted at approximately what height above the finished floor?
Access Control Installation
2. A magnetic lock is inherently which fail mode, and why?
Safety and Work Practices
3. Before energizing a newly installed access control system, what action is required according to best practice?
Access Control Installation
4. A door position switch is wired to a normally-closed (NC) controller input. When the door is opened, what signal does the controller receive?
Access Control Installation
5. An installer leaves a gap between a magnetic lock's armature plate and the magnet face. What is the primary consequence of this error?
Codes and Standards
6. Which fail mode is generally required by life-safety codes for the primary egress door of an occupied building?
Troubleshooting and Service
7. A passive infrared (PIR) REX sensor mounted on the secured side of a door fails to release the magnetic lock when a person approaches to exit. After confirming the sensor has power, what is the most likely wiring fault to check first?
Access Control Installation
8. During an electric strike installation, a feeler gauge shows the door gap is 0.063 inch (1/16 inch) and the manufacturer specifies 0.125 inch (1/8 inch). What problem is most likely to result if the installation proceeds without adjustment?
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