North Carolina Low Voltage Practice cheat sheet

Class 2/3 circuits are power-limited per Article 725; Class 2 limits are 100 VA or less and 30 V or less, Class 3 exceeds Class 2 limits but stays within Table 725.144 or 725.121 listings.

CL2P/CL3P plenum cable is required in ducts, plenums, and other air-handling spaces; CL2R/CL3R riser cable is for vertical runs in shafts; CL2/CL3 is for general-purpose use.

Communications cable substitutions allowed by 800.154: CMP may replace CMR, CM, CMG; CMR may replace CM and CMG; CMG may replace CM in one- and two-family dwellings only.

Separation from Class 1 circuits: Class 2/3 cables must be separated by at least 2 inches from Class 1 conductors unless the Class 1 wiring uses a Chapter 3 wiring method or the Class 2/3 cable is in a raceway or has a nonconductive sheath.

Support horizontal cable at intervals not exceeding 4.5 ft (1.4 m) and within 12 in of boxes; do not exceed 25 lb (11 kg) of pulling tension on 4-pair copper cable.

Minimum bend radius for 4-pair UTP is 4x cable diameter (about 1 in for 0.25 in cable); for fiber, follow manufacturer ratings-typically 10x diameter for installation and 1.5 in for a 2 mm cord.

Raceway fill for communications cable is governed by Chapter 9 tables and Note 9; do not exceed 40 percent fill for three or more cables in a conduit.

Abandoned cable must be removed unless it is identified for future use with a tag; this applies to communications, Class 2/3, and optical fiber cables.

Ohm's law: E = I x R; power: P = E x I = I²R = E²/R. For a 24 V circuit drawing 0.5 A, P = 12 W and R = 48 ohms.

Voltage drop for DC or single-phase: VD = 2 x K x I x L / CM, where K = 12.9 for copper and 21.2 for aluminum, L in feet, CM in circular mils.

Three-phase voltage drop: VD = 1.732 x K x I x L / CM; use this for three-phase feeders and motors.

Voltage divider for series circuits: Vx = Vs x Rx / Rtotal. Current is the same through all series elements; voltage is the same across all parallel branches.

AWG circular mils: 18 AWG = 1,620; 16 AWG = 2,580; 14 AWG = 4,110; 12 AWG = 6,530; 10 AWG = 10,380; 8 AWG = 16,510.

Power-limited circuit current: I = P / E. A 100 VA Class 2 source at 24 V delivers 4.17 A maximum; at 12 V it delivers 8.33 A.

Ampacity derating: apply Table 310.16 correction factors for ambient temperature and Table 310.15(C)(1) adjustment for more than three current-carrying conductors in a raceway.

Series-parallel simplification: reduce parallel pairs with Rp = (R1 x R2)/(R1 + R2), then add series resistances to find total load and source current.

Article 725 covers Class 1, Class 2, and Class 3 remote-control and signaling circuits; Article 760 covers fire alarm systems; Article 770 covers optical fiber; Article 800 covers communications circuits; Article 820 covers CATV and radio distribution.

Article 760 Part III applies to NPLFA (non-power-limited fire alarm) circuits; Part IV applies to PLFA (power-limited fire alarm) circuits. PLFA cable types include FPLP (plenum), FPLR (riser), and FPL (general).

Article 800 communications cables: CMP, CMR, CM, CMG, CMX. Outdoor and buried cable must be listed for the environment (e.g., OSP, direct burial) or installed in a Chapter 3 raceway.

Article 820 CATV cable types: CATVP (plenum), CATVR (riser), CATV, CATVX. Coaxial cable shields must be bonded to the grounding electrode system at the building entry.

North Carolina adopts the NEC with state amendments through the NC State Board of Examiners of Electrical Contractors; the current statewide edition is the 2023 NEC with NC amendments effective in 2023-2024.

NC licensing: a low voltage contractor must hold an electrical contracting license issued by the NC State Board of Examiners of Electrical Contractors; the SP-LV (Special Restricted) license covers low voltage work up to 50 volts.

Section 110.14 governs conductor terminations; 110.26 working clearances (36 in depth for 0-150 V to ground, 30 in width, 6.5 ft height) apply to low voltage equipment rooms as well as service equipment.

Section 300.22 governs wiring in ducts and plenums; only plenum-rated cable or cable in metallic raceway may be installed in environmental air spaces.

Article 250 applies to grounding and bonding of power systems; Articles 800.100, 820.100, and 810.58 provide separate bonding requirements for communications, CATV, and radio antenna systems.

Communications bonding conductor must be at least 14 AWG copper, listed, and run as short and straight as practicable; length should not exceed 20 ft (6 m) where practicable.

Bond communications and CATV shields to the building's grounding electrode system, the service equipment enclosure, the grounded service conductor, or a grounding electrode conductor-not to a separate isolated ground rod.

Grounding electrode system per 250.50 includes metal water pipe (10 ft in contact with earth), metal building frame, concrete-encased electrode (20 ft of 1/2 in rebar or 4 AWG bare copper), ground rod (8 ft, 25 ohms or less), and plate electrodes.

Bonding jumpers around water meters and other removable fittings are required; a single continuous conductor or irreversible connection must be maintained.

Equipment grounding conductors (EGC) must be sized per Table 250.122 based on overcurrent device rating; for a 20 A circuit, 12 AWG copper EGC is the minimum.

Separately derived systems require a system bonding jumper; the grounded conductor is not bonded to ground on the load side of the first disconnecting means.

GFCI and AFCI protection: GFCI required in bathrooms, kitchens, garages, outdoors, and near sinks; AFCI required for most 15/20 A branch circuits in dwellings per 210.12.

NFPA 72 governs fire alarm installation; the NEC Article 760 governs the wiring methods. Both must be satisfied for a compliant system.

Initiating devices include smoke detectors, heat detectors, pull stations, and waterflow switches. Notification appliances include horns, strobes, chimes, and speakers.

Class A circuits survive a single open; Class B circuits do not. Class A requires a return path to the panel; Class B is a two-wire loop that terminates at the last device.

Smoke detector spacing: 30 ft (9.1 m) maximum between detectors on a smooth ceiling, 15 ft from a wall or obstruction; spot-type detectors must be at least 3 ft from air supply diffusers.

Notification appliance circuits (NAC) are typically 24 VDC and power-limited; voltage drop calculation must ensure at least the appliance's rated minimum voltage at the end of the circuit.

Surveillance and security systems: intrusion detection circuits are Class 2 or Class 3 per Article 725; camera and access control cabling follows Article 800 requirements.

Battery backup for fire alarm: secondary supply must be sized for 24 hours of standby plus 5 minutes of alarm for commercial systems (NFPA 72); 24 hours plus 15 minutes for voice evacuation.

Fire alarm cable in plenum spaces must be FPLP; in risers FPLR; general use FPL. Power-limited fire alarm cable is marked with the appropriate listing.

TIA-568 defines structured cabling categories: Cat 5e (100 MHz), Cat 6 (250 MHz), Cat 6A (500 MHz), Cat 8 (2000 MHz). Maximum horizontal channel length is 100 m (90 m permanent link plus 10 m of patch cords).

Cat 6A is required for 10GBASE-T beyond 55 m; Cat 6 supports 10GBASE-T up to 55 m; Cat 5e is limited to 1000BASE-T (1 Gbps) at 100 m.

Fiber types: OM1 (62.5/125 µm, 200/500 MHz·km), OM2 (50/125, 500/500), OM3 (50/125, 2000/500), OM4 (50/125, 4700/500); OS2 single-mode for long distances. Use 850 nm VCSELs with OM3/OM4.

Fiber connectors: LC (1.25 mm ferrule), SC (2.5 mm), ST (bayonet). APC connectors use an 8° angled polish and are not intermateable with UPC.

T568A and T568B pinouts differ in pairs 2 and 3 (green/orange). Either is acceptable but must be consistent across the installation.

Horizontal cabling topology is star; consolidation point and MUTOAs are permitted; no more than one transition point per horizontal run.

Audio/video distribution: HDMI, DisplayPort, and HDBaseT have distance limits (HDMI typically 15 m passive, HDBaseT 100 m over Cat 6). Use active extenders or fiber for longer runs.

Grounding and shielding: shielded twisted pair (STP/FTP) requires proper bonding at both ends to the telecommunications grounding busbar (TGB); unshielded twisted pair does not require shield bonding.

NC electrical contracting license classes: Limited (up to 600 V, single-phase and three-phase), Intermediate (up to 600 V, unlimited), Unlimited (any voltage). The SP-LV special restricted license covers low voltage only.

License renewal: NC electrical licenses renew annually; continuing education (8 hours per year) is required for licensees. Verify current cycle requirements with the NC State Board of Examiners of Electrical Contractors.

Bidding and contracts: a written contract should specify scope, schedule, payment terms, change-order procedures, warranty, and dispute resolution. Oral contracts are enforceable but harder to prove.

Lien rights: NC provides mechanics' and materialmen's liens; a Notice to Lien Agent is required on projects over $30,000 for subs and suppliers on improved real property.

Permits and inspections: most low voltage work requires a permit from the local AHJ; inspections must be passed before concealment. The AHJ has final authority on code interpretation.

OSHA: 29 CFR 1926 Subpart K covers electrical safety in construction; lockout/tagout (1910.147) applies when servicing energized equipment.

Insurance: general liability, workers' compensation (required in NC for employers with 3+ employees), and auto liability are typical minimums for a low voltage contractor.

NC contractor licensing: a general contractor license is required for projects over $30,000; electrical work requires a separate electrical license from the Board of Examiners.

Use a CAT III or CAT IV rated multimeter for measurements on distribution circuits; CAT II is for portable equipment, CAT III for distribution, CAT IV for service entrance.

Lockout/tagout: verify de-energization with a tester rated for the voltage, apply a lock and tag, and confirm zero energy before work.

PPE: safety glasses with side shields, hard hat, and Class 0 (1000 V) insulating gloves when working near energized equipment; arc-rated clothing per NFPA 70E for higher-risk tasks.

Ladder safety: 4-to-1 rule-base 1 ft out for every 4 ft of working height; maintain three points of contact; do not stand on the top two rungs of a stepladder.

Confined space entry requires atmospheric testing (O2, LEL, H2S, CO), a permit, an attendant, and rescue plan per OSHA 1910.146.

Cable pulling: use lubricant rated for the jacket, do not exceed manufacturer tension limits (typically 25 lb for 4-pair UTP, 100 lb for fiber), and use a swivel to prevent twisting.

Tool safety: inspect cords and tools for damage; use GFCI-protected outlets on construction sites; never modify a plug to bypass the ground pin.

Fire stop penetrations through rated walls and floors with listed materials; maintain the fire-resistance rating of the assembly.