Georgia Low Voltage Practice flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Ohm's Law

Voltage equals current times resistance (E = I × R). Rearranged, I = E/R and R = E/I. It applies to DC circuits and to AC circuits only when impedance replaces resistance.

Voltage Drop Formula

For a two-conductor run, VD = 2 × K × I × L / CM, where K is 12.9 for copper, I is amperes, L is one-way feet, and CM is circular mils. Keep low voltage drops under about 5 percent.

Parallel Circuit Rules

Voltage is the same across every branch, total current is the sum of branch currents, and total resistance is found from the reciprocal sum. Total resistance is always less than the smallest branch resistance.

Class 2 Versus Class 3

Both are power-limited circuits under NEC Article 725. Class 2 has lower energy limits, while Class 3 permits higher voltage and current but still requires separation from power conductors and listed cable.

Plenum Cable Rating

CMP cable is listed for installation in air-handling spaces because its jacket has low smoke and flame spread. CMR is for risers, CM for general use, and CMX for limited exposed residential use.

UTP Bend Radius

Four-pair UTP is typically limited to four times the cable diameter during installation and about ten times during a pull. Violating the radius deforms the pair geometry and raises return loss.

NEC Article 725 Scope

Article 725 governs Class 1, Class 2, and Class 3 remote-control, signaling, and power-limited circuits. It sets circuit classification, cable marking, separation, and installation requirements for low voltage work.

NEC Article 800 Scope

Article 800 covers communications circuits and cables, including the CM, CMR, CMP, and CMX markings. It addresses installation, separation from power, grounding, and protection of communications circuits.

NEC Working Clearance

Section 110.26 requires at least 3 ft of depth, 30 in. of width, and 6.5 ft of height in front of equipment likely to be examined while energized, plus dedicated space above.

TIA-568 Channel Length

A horizontal channel is limited to 100 m total: 90 m of permanent horizontal cable plus up to 10 m of patch cords. The permanent link excludes cords and is tested to a tighter limit.

T568B Pinout

In T568B, pins 1-2 are the orange pair, 3-6 the green pair, 4-5 the blue pair, and 7-8 the brown pair. T568A swaps the orange and green pairs; both ends must match.

Single-Mode Versus Multimode

Single-mode fiber has an 8-10 micron core and carries 1310 or 1550 nm laser light for long distances. Multimode is 50 or 62.5 microns and uses 850 or 1300 nm sources for shorter runs.

Class A Versus Class B SLC

A Class B signaling line circuit tolerates one open or ground fault but loses devices beyond the break. A Class A circuit returns to the panel so a single fault does not disable any device.

Smoke Detector Spacing

On a smooth ceiling, listed detectors are spaced up to 30 ft apart with a 21 ft maximum distance to a wall or obstruction. Use the manufacturer's listed spacing when it is smaller.

Fire Alarm Cable Ratings

FPL is general-purpose fire alarm cable, FPLR is rated for risers, and FPLP is rated for plenum spaces. The suffix must match the environment, and the cable must be listed for fire alarm use.

Manual Pull Station Height

Manual fire alarm pull stations are mounted 42 to 48 in. above the finished floor, within 5 ft of an exit door, and on the latch side unless the listing or the authority having jurisdiction states otherwise.

End-of-Line Resistor

An EOL resistor terminates a supervised alarm zone so the panel can detect opens and shorts. Normal, alarm, and trouble states are distinguished by the loop's measured resistance.

Wiegand 26-Bit Format

Wiegand 26-bit carries an 8-bit facility code and a 16-bit card number, plus parity bits. It uses DATA0 and DATA1 lines at roughly 5 V differential and offers no encryption.

OSDP Protocol

Open Supervised Device Protocol runs over RS-485, supports encrypted bidirectional communication, and allows multiple readers on one bus. It is the modern replacement for Wiegand in access control.

Fail-Safe Versus Fail-Secure

Fail-safe locks unlock when power is lost and are required on egress doors. Fail-secure locks remain locked on power loss and are used only where life safety is not compromised.

PoE Power Classes

IEEE 802.3af supplies up to 15.4 W, 802.3at up to 30 W, and 802.3bt up to 60 or 100 W at the source. Cable heating and distance reduce the power available at the device.

Balanced Audio

Balanced audio uses two conductors carrying equal but opposite signals plus a shield. The receiver subtracts the difference, canceling common-mode noise, which allows long microphone and line-level runs.

Constant-Voltage Audio

Distributed 70.7 V or 100 V audio systems use a transformer at each speaker. The sum of the speaker tap wattages must not exceed the amplifier's rated output wattage.

RS-485 Termination

RS-485 buses are half-duplex and multi-drop, requiring 120 ohm termination at both physical ends plus bias resistors. Star wiring causes reflections and unreliable communication.

Grounding Versus Bonding

Grounding connects equipment to earth, while bonding connects metal parts together to equalize potential. Bonding is what clears faults and limits touch voltage during a fault.

SPD Types

Type 1 surge protective devices install at the service entrance, Type 2 at distribution panels, and Type 3 at the point of use. Coordinating types reduces let-through voltage at downstream equipment.

SPD Lead Length

Surge protective device leads should be as short and straight as possible. Long or looped leads add inductive voltage drop that raises the clamping voltage seen by the protected equipment.

TIA-607 Bonding

ANSI/TIA-607 requires a telecommunications bonding busbar connected to the building grounding electrode system through a telecommunications bonding conductor, bonding all telecommunications infrastructure.

Test Before Touch

Verify the meter on a known live source, test the circuit, then re-verify the meter. A meter that fails during a live test can display a false zero and create a shock hazard.

Extension Ladder Rule

Extension ladders use a 4-to-1 base-to-height ratio, maintain three points of contact, and extend at least 3 ft above the landing when used for roof or platform access.

Lockout Tagout Steps

Locate the disconnecting means, apply a lock and tag, release stored energy, and verify zero energy with a tested meter. Only the person who applied the lock may remove it.

Georgia Qualifying Agent

A Georgia low voltage contractor license is held by the business and requires a qualifying agent who passes the exam and meets experience requirements. The agent must be actively involved in the work.

Georgia Mechanic's Lien

A contractor who furnishes labor or materials may file a mechanic's lien on the improved property. In Georgia the lien is generally filed within 90 days of last furnishing and then perfected by suit.