Low Voltage Tech Exam Questions & Answers 2026 (21–30)

Question 1

What is the purpose of the 'anti-passback' feature in an access control system?

TheoryPractice · Accepted Answer

To prevent a credential from being used to re-enter an area without first exiting. Anti-passback prevents a credential from being used to enter a zone again unless it has first been used to exit. This prevents credential sharing (passing the card back through a door) and improves occupancy tracking accuracy.

Question 2

In a 'soft' anti-passback configuration, what happens when a violation is detected?

TheoryPractice · Accepted Answer

Access is still granted but an alert/event is logged. Soft anti-passback still grants access when a violation occurs but records the event for review. Hard anti-passback denies access when a violation is detected. Soft anti-passback is useful during rollout when tailgating may be common.

Question 3

The 'two-man rule' (dual custody) in access control requires:

TheoryPractice · Accepted Answer

Two authorized individuals to each present their credential before access is granted. The two-man rule requires two separate, authorized individuals to each authenticate independently before a door will open. This is common in high-security environments such as data centers, vaults, and critical infrastructure.

Question 4

To reduce electrical interference on Wiegand data lines from readers to controllers, what technique is commonly used?

TheoryPractice · Accepted Answer

Using shielded twisted-pair cable with the shield grounded at one end. Shielded twisted-pair cable helps reject EMI/RFI interference on the data lines. The shield should be grounded at one end only (typically the controller end) to prevent ground loops. Running parallel to AC power should be avoided.

Question 5

RS-485 communication is used in access control systems primarily because it:

TheoryPractice · Accepted Answer

Supports long cable runs (up to 4,000 feet) and multiple devices on a single bus. RS-485 is a balanced differential signaling standard that supports cable runs up to approximately 4,000 feet (1,200 m) and allows up to 32 (or more with repeaters) devices on a single bus, making it ideal for distributed access control panels.

Question 6

In an RS-485 multi-drop network for access control, termination resistors are placed:

TheoryPractice · Accepted Answer

At both ends of the cable run (at the first and last device). RS-485 requires 120-ohm termination resistors at both ends of the bus—at the host/controller and at the last device—to absorb signal reflections and prevent data corruption. Adding them at every node would degrade the signal.

Question 7

In an IP-based access control system, the controller connects directly to the network. A key advantage of this architecture over a traditional panel-and-subpanel design is:

TheoryPractice · Accepted Answer

Each door controller can be managed individually via the network without a dedicated head-end panel. IP-based (network-based) access controllers connect directly to the LAN, allowing each unit to be independently managed via software. This offers flexibility, scalability, and easier integration with other networked systems compared to traditional RS-485 architectures.

Question 8

OSDP (Open Supervised Device Protocol) offers which major security advantage over legacy Wiegand?

TheoryPractice · Accepted Answer

Bidirectional, encrypted, and authenticated communication between reader and controller. OSDP uses AES-128 encrypted, bidirectionally authenticated communication, preventing eavesdropping and replay attacks that are possible with the unencrypted, one-way Wiegand protocol. OSDP also supports reader status reporting and firmware updates.

Question 9

OSDP Secure Channel mode uses which encryption standard to protect reader-to-controller communication?

TheoryPractice · Accepted Answer

AES-128. OSDP v2 Secure Channel mode uses AES-128 (Advanced Encryption Standard with a 128-bit key) for encrypting reader-to-controller communication. This prevents interception attacks that were trivially possible with unencrypted Wiegand protocols.

Question 10

What is 'card enrollment' in an access control system?

TheoryPractice · Accepted Answer

Registering a credential in the system database and assigning it to a cardholder with specific access levels. Card enrollment is the process of registering a credential (card, fob, mobile credential) in the access control database, associating it with a specific person, and assigning the appropriate access levels (doors + schedules).

Low Voltage Tech Exam Questions & Answers 2026 (21–30)

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