Arizona Low Voltage Practice cheat sheet

Ohm's Law: E = I × R; I = E ÷ R; R = E ÷ I, where E is volts, I is amperes, and R is ohms.

Power formulas: P = E × I; P = I² × R; P = E² ÷ R. One watt equals one volt-ampere only at unity power factor.

Series circuit: current is identical through every element; resistances add (R_total = R1 + R2 + ...); voltage divides in proportion to resistance.

Parallel circuit: voltage is identical across every branch; conductances add, so 1/R_total = 1/R1 + 1/R2 + ...; branch currents sum to the total.

Class 2 circuits are power-limited by listed transformers or supplies; NEC Table 11(A) and 11(B) of Chapter 9 set the voltage and current limits.

Voltage drop for a two-wire run: VD = 2 × K × I × L ÷ CM, where K ≈ 12.9 for copper and 21.2 for aluminum, L in feet, CM in circular mils.

Circular mils: CM = d² where d is the conductor diameter in mils (thousandths of an inch); 1 mil = 0.001 inch.

Ampacity of a low-voltage conductor is selected from the applicable table by insulation type and ambient temperature, then corrected for conduit fill and temperature.

Article 725 covers Class 1, Class 2, and Class 3 remote-control and signaling circuits; Article 800 covers communications circuits; Article 820 covers coaxial cable for CATV and radio distribution.

Class 2 and Class 3 cables must be separated from electric light and power conductors by at least 2 inches (50 mm) unless the power conductors are in a raceway, are nonmetallic-sheathed cable, or the cables are separated by a permanent barrier.

Cable substitution rules: a cable with a higher fire-resistance or circuit-integrity rating (for example CMP in place of CMR or CM) may substitute for a lower-rated cable, but never the reverse.

Cable markings: CMP is plenum rated, CMR is riser rated, CM is general purpose, and CMX is limited to residential and raceway use; the suffix G denotes a grounding conductor included in the cable.

Support intervals: communications cables are generally supported at intervals not exceeding 4.5 feet (1.4 m) and within 12 inches (300 mm) of boxes, unless installed in a raceway or listed raceway-type support.

Bend radius: a four-pair balanced twisted-pair cable must not be bent tighter than four times the cable diameter during installation and eight times the diameter after installation.

Cable tray fill for communications cables is limited to 50 percent of the interior cross-sectional area of the tray for multiconductor cables; single conductors are limited to 50 percent as well.

Openings through fire-rated assemblies must be sealed with a listed firestop system approved for the specific cable type and penetration configuration.

Article 250 distinguishes the grounding electrode conductor, the equipment grounding conductor, and the main bonding jumper; each serves a different function and is sized separately.

Low-voltage systems are grounded per the manufacturer's listing and Article 250 requirements; Class 2 and Class 3 circuits are generally not grounded unless required by the equipment listing.

Bonding is the intentional connection of metallic parts to form an electrically conductive path; grounding is the connection to earth. Bonding is what clears faults; grounding alone does not.

Telecommunications bonding conductor sizing follows NEC Table 800.100(A): for example, 14 AWG copper for a conductor up to 6 feet long, 12 AWG up to 10 feet, 6 AWG up to 18 feet.

A listed primary protector is required where communications conductors enter a building, and it must be bonded to the building's grounding electrode system as close as practicable to the entry point.

Ground-fault circuit interrupter protection is required in wet locations, bathrooms, kitchens, garages, outdoors, and within 6 feet of sinks, per Article 210.8.

Overcurrent protection for low-voltage power supplies is provided by the listed Class 2 or Class 3 transformer or supply; the transformer's inherent impedance limits available fault current.

Equipment grounding conductors must be continuous, electrically connected to every box and enclosure, and sized per NEC Table 250.122 based on the overcurrent device rating.

NFPA 72 governs fire alarm system installation, inspection, testing, and maintenance; NFPA 101 governs life safety and means of egress.

Initiating devices include smoke detectors, heat detectors, duct detectors, waterflow switches, and manual pull stations; notification appliances include horns, strobes, speakers, and combination units.

Smoke detector spacing: 30 feet (9.1 m) maximum between detectors on a smooth ceiling, with the first detector within 15 feet (4.6 m) of any wall and at least 4 inches (100 mm) from the wall.

Heat detector spacing depends on the listing: 50 feet for ordinary 135–174°F fixed-temperature units on smooth ceilings, reduced for high ceilings per NFPA 72 spacing reduction factors.

Notification appliance circuits (NACs) must be supervised and powered per the manufacturer's voltage-drop calculation; the operating voltage at the last appliance must meet the listed minimum.

Survivable fire alarm cable is designated CI (circuit integrity) and must be installed per the listing; FPLR and FPLP cables are for riser and plenum use respectively.

A fire alarm control unit must be located in an area accessible to authorized personnel and, when required, in a room with a 1-hour or 2-hour fire-resistance rating per the building code.

Inspection, testing, and maintenance frequencies: monthly for some supervisory devices, quarterly for others, annually for most initiating and notification devices, and sensitivity testing of smoke detectors per the manufacturer's schedule.

Access control reader types: proximity (125 kHz or 13.56 MHz), magnetic stripe, keypad, biometric, and mobile credential; Wiegand is a common legacy interface at 26 to 40 bits.

Fail-safe locks unlock on loss of power (used on egress doors); fail-secure locks remain locked on loss of power. Egress doors must release with a single operation without a key or special knowledge.

Request-to-exit devices include push buttons, passive infrared sensors, and exit switches; they must be wired so the door releases reliably and are typically on a separate supervised input.

Balanced twisted-pair cable characteristics: 100 ohms nominal impedance, Category 5e rated to 100 MHz, Category 6 to 250 MHz, Category 6A to 500 MHz.

PoE standards: 802.3af delivers up to 15.4 W at the source (12.95 W at the device); 802.3at (PoE+) delivers up to 30 W (25.5 W at the device); 802.3bt delivers up to 60 W or 90 W.

CCTV camera resolution: analog NTSC is 704 × 480 effective; IP cameras commonly deliver 1080p (1920 × 1080) or 4K (3840 × 2160). Lens focal length and sensor size set the field of view.

Video storage sizing: storage in bytes ≈ bit rate (bits per second) × 3600 × hours ÷ 8, summed across all cameras and adjusted for retention days.

Coaxial CCTV uses 75-ohm cable (RG-59 or RG-6); the nominal 1-volt peak-to-peak composite video signal must be maintained at the monitor input.

T568A and T568B are the two wiring pin assignments for eight-position modular jacks; both are acceptable, but one standard must be used consistently throughout a project.

A straight-through patch cord uses the same pinout at both ends; a crossover cord reverses transmit and receive pairs and is used only for legacy direct device-to-device links.

Horizontal cabling maximum distance is 90 meters (295 feet) of permanent link plus 10 meters (33 feet) of patch cords, for a 100-meter channel.

TIA-568 categories: Cat 3 to 16 MHz, Cat 5e to 100 MHz, Cat 6 to 250 MHz, Cat 6A to 500 MHz, Cat 8 to 2000 MHz at 30 meters.

Fiber optic cable: single-mode has a 9-micron core and long reach; multimode is 50 or 62.5 microns with shorter reach. Connector types include LC, SC, and ST.

Audio distribution: 70.7-volt and 100-volt constant-voltage systems allow many speakers on one line; total speaker wattage taps must not exceed the amplifier's rated output.

Video distribution over twisted pair uses baluns to convert unbalanced coaxial video to balanced twisted pair; passive baluns work over limited distances, active baluns extend range.

Separation from power: keep unshielded twisted pair at least 2 inches from power conductors and cross power lines at 90 degrees to minimize induced noise.

The Arizona Registrar of Contractors (ROC) licenses and regulates contractors under A.R.S. Title 32, Chapter 10; low-voltage work falls under the L-67 low voltage communication and electrical systems classification.

A licensed contractor must have a qualifying party who passes the trade and business management examinations; the license is issued to the entity, not the individual.

Advertising, bids, and contracts must show the ROC license number; unlicensed contracting is a class 1 misdemeanor for a first offense and can become a felony for repeat offenses.

Contract limits: bids and contracts for residential work over $1,000 in labor and materials require a licensed contractor; commercial work has no dollar threshold for licensure.

The ROC requires a written contract for residential work and, for certain projects, a disclosure statement; payment terms and a three-day right of rescission apply to some home solicitation contracts.

Arizona requires a permit and inspection for most electrical work; low-voltage cabling may require a permit depending on the jurisdiction, and the authority having jurisdiction makes the final determination.

OSHA safety: lockout/tagout per 29 CFR 1910.147, fall protection above 6 feet in construction per 1926.501, and a written hazard communication program per 1910.1200.

Personal protective equipment and safe practices: verify absence of voltage with a tested meter before working, use insulated tools, and never work alone on energized equipment above 50 volts.