TheoryLow Voltage Tech
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30 free Low Voltage Tech questions
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Access Control
What is the primary purpose of an access control system?
Correct — C. Access control systems are designed to allow only authorized individuals to enter specific areas while keeping out unauthorized persons. This protects assets, personnel, and sensitive information. -
Access Control
Which type of credential stores data on a microchip embedded in the card?
Correct — A. Smart cards contain an embedded microchip that stores and processes data. Unlike magnetic stripe or barcode cards, smart cards can hold more data and support cryptographic operations for enhanced security. -
Access Control
A proximity card reader typically operates at which frequency?
Correct — B. Traditional proximity cards operate at 125 kHz (low frequency). This distinguishes them from high-frequency smart cards (13.56 MHz) used in more modern contactless systems. -
Access Control
Which of the following is an example of a biometric credential?
Correct — D. Biometric credentials are based on unique physical or behavioral characteristics of an individual, such as fingerprints, iris patterns, or facial recognition. PINs, cards, and key fobs are not biometrics. -
Access Control
In access control terminology, what does 'authentication' refer to?
Correct — A. Authentication is the process of verifying identity—confirming that the person presenting credentials is indeed who they claim to be. Authorization (granting access) is a separate step that follows authentication. -
Access Control
An electric strike holds the door closed when de-energized and releases when energized. This configuration is known as:
Correct — B. Fail-safe (also called fail-open) means the lock releases when power is lost, allowing free egress—important for life-safety reasons. Fail-secure means the lock remains locked when power is removed. -
Access Control
What device is used to prevent 'tailgating' (piggybacking) at a secured entrance?
Correct — C. A mantrap (security vestibule/airlock) uses two interlocked doors so only one person can enter at a time, preventing tailgating. The second door will not open until the first closes and the individual is verified. -
Access Control
The three factors of authentication are 'something you know,' 'something you have,' and:
Correct — D. The three classic authentication factors are: (1) something you know (PIN, password), (2) something you have (card, token), and (3) something you are (biometric characteristic). Multi-factor authentication uses two or more of these. -
Access Control
What wire gauge is commonly used for access control reader wiring runs under 500 feet?
Correct — A. 22 AWG (American Wire Gauge) multi-conductor cable is the standard for access control reader data and power runs up to approximately 500 feet. Heavier gauges (lower AWG numbers) are used for longer runs or higher current loads. -
Access Control
What does 'HID' stand for in the access control industry?
Correct — B. HID stands for HID Global, originally Hughes Identification Devices. HID is one of the leading manufacturers of access control credentials, readers, and related technology. -
Access Control
What is the function of an access control panel (also called an access controller)?
Correct — C. The access control panel (controller) is the brain of the system. It receives credential data from readers, compares it to its database, and makes a grant or deny decision, then sends the appropriate signal to the door hardware. -
Access Control
In biometric systems, what does the term 'False Acceptance Rate' (FAR) measure?
Correct — D. FAR (False Acceptance Rate) is the frequency at which an unauthorized person is incorrectly accepted by the biometric system. A lower FAR means higher security. It is paired with FRR (False Rejection Rate), which measures how often authorized users are denied. -
Access Control
Which biometric modality is generally considered the most accurate and difficult to spoof?
Correct — A. Iris recognition has one of the highest accuracy rates among biometric modalities due to the unique and stable pattern of the iris. It is also difficult to spoof compared to fingerprints or facial recognition. -
Access Control
In a standard 26-bit Wiegand card format, how many bits are allocated to the card number?
Correct — C. In the 26-bit Wiegand format, 16 bits are used for the card number, 8 bits for the facility code, and 2 bits for parity. The 16-bit card number allows for card numbers ranging from 0 to 65,535. -
Access Control
A magnetic lock (maglocks) releases when power is removed. What is the typical holding force of a standard single-door maglock?
Correct — A. A standard single-door electromagnetic lock has a holding force of approximately 1,200 lb (545 kg). Double-door versions and higher-security units can achieve higher holding forces, while lighter-duty locks may hold less. -
Access Control
Which hardware component monitors whether a door is physically open or closed and reports that status to the access control panel?
Correct — D. A door position switch (DPS), typically a magnetic contact, monitors the physical open/closed state of the door and reports it to the controller. This allows detection of forced entry or doors held open too long. -
Access Control
What is the purpose of a Request-to-Exit (REX) device in an access control system?
Correct — B. A REX device (motion sensor, push button, or bar) detects legitimate egress and tells the controller to suppress the door-forced alarm and/or unlock the door for exit. Without it, the system would trigger an alarm every time someone exits. -
Access Control
Most access control panels and door hardware operate on which voltage?
Correct — C. Access control panels and most door hardware (strikes, maglock, readers) are designed to operate on 12 VDC or 24 VDC supplied by a power supply with battery backup. This low-voltage DC design keeps installers under low-voltage licensing requirements. -
Access Control
In access control software, an 'access level' defines:
Correct — D. An access level (also called an access group or access profile) combines a list of doors with time schedules and assigns this combination to credential holders. It answers: 'Who can get into which doors and when?' -
Access Control
What function in access control software allows a credential to unlock a door for a set period of time, after which normal time-schedule restrictions resume?
Correct — B. A temporary access override or extended grant allows a manager to grant a credential holder temporary access beyond normal schedule restrictions for a defined period, after which normal rules automatically resume. -
Access Control
What is the purpose of the 'anti-passback' feature in an access control system?
Correct — C. 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. -
Access Control
In a 'soft' anti-passback configuration, what happens when a violation is detected?
Correct — A. 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. -
Access Control
The 'two-man rule' (dual custody) in access control requires:
Correct — D. 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. -
Access Control
To reduce electrical interference on Wiegand data lines from readers to controllers, what technique is commonly used?
Correct — C. 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. -
Access Control
RS-485 communication is used in access control systems primarily because it:
Correct — A. 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. -
Access Control
In an RS-485 multi-drop network for access control, termination resistors are placed:
Correct — D. 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. -
Access Control
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:
Correct — B. 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. -
Access Control
OSDP (Open Supervised Device Protocol) offers which major security advantage over legacy Wiegand?
Correct — A. 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. -
Access Control
OSDP Secure Channel mode uses which encryption standard to protect reader-to-controller communication?
Correct — D. 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. -
Access Control
What is 'card enrollment' in an access control system?
Correct — B. 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 sample questions
Tap any question below to reveal the answer and a plain-English explanation.
Access Control When a cardholder's employment is terminated, what is the correct immediate action regarding their access credential?
A. Transfer the credential to another employee
B. Leave the credential active until the end of the month
C. Deactivate (disable) or delete the credential from the system immediately ✓
D. Change the PIN on the credential
Correct — C. Immediate deactivation of a terminated employee's credential is a critical security practice. Leaving credentials active after termination is a significant vulnerability that can enable unauthorized access or insider threats.
Structured Cabling Which category of unshielded twisted-pair (UTP) cable is the minimum required to support Gigabit Ethernet (1000BASE-T)?
A. Cat 3
B. Cat 5
C. Cat 5e ✓
D. Cat 6
Correct — C. Cat 5e (enhanced) is the minimum category rated for 1000BASE-T. It reduces crosstalk compared to standard Cat 5 and meets the performance requirements for Gigabit Ethernet over 100 m.
Fire Alarm Systems What is the primary function of a Fire Alarm Control Unit (FACU)?
A. To monitor initiating devices and activate notification appliances ✓
B. To suppress fires using chemical agents
C. To provide backup power to all building systems
D. To communicate directly with the fire department
Correct — A. The FACU monitors all connected initiating devices (detectors, pull stations) for alarm conditions and, when triggered, activates notification appliances (horns, strobes) and performs other programmed functions. Suppression, backup power to all systems, and direct fire-department communication are separate functions.
NEC Low-Voltage Code Under NEC Article 725, Class 1 remote-control circuits are permitted to operate at a maximum voltage of:
A. 600 volts ✓
B. 150 volts
C. 300 volts
D. 1000 volts
Correct — A. Article 725.41 limits Class 1 remote-control and signaling circuits to 600 V or less. Class 2 and Class 3 circuits have lower voltage ceilings.
Networking Basics How many layers does the OSI reference model have?
A. 5
B. 7 ✓
C. 4
D. 6
Correct — B. The OSI (Open Systems Interconnection) model defines 7 layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application. This standardized framework describes how data travels across a network.
Safety Which minimum voltage rating is required for insulated gloves used when working on low-voltage electrical equipment?
A. 1000 V AC ✓
B. 500 V AC
C. 250 V AC
D. 100 V AC
Correct — A. OSHA and NFPA 70E require Class 00 or higher rubber insulating gloves rated at least 1000 V AC for work on energized low-voltage (up to 1000 V) circuits. Lower-rated gloves do not provide adequate protection.
Security & CCTV What does the acronym CCTV stand for?
A. Central Camera Television Viewfinder
B. Closed Channel Tele-Video
C. Closed-Circuit Television ✓
D. Centralized Control Television Vision
Correct — C. CCTV stands for Closed-Circuit Television, meaning the video signal is transmitted to a limited set of monitors rather than broadcast publicly. It is used in security and surveillance applications.
Electrical Theory A circuit has a voltage of 12 V and a resistance of 4 Ω. What is the current?
A. 48 A
B. 0.33 A
C. 3 A ✓
D. 8 A
Correct — C. Ohm's Law: I = V / R = 12 / 4 = 3 A. Dividing voltage by resistance gives current.
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