US National Electrical Code (NEC, NFPA 70): 120/240 V 60 Hz, AWG wiring, GFCI and AFCI protection, ampacity tables, differences from PUE and IEC.
| Document | NEC — National Electrical Code (NFPA 70) |
| Voltage | 120/240 V |
| Frequency | 60 Hz |
| Sockets | NEMA 5-15R etc. |
| Earthing | TN-C-S (grounded neutral + equipment ground) |
| Native term | Transliteration | English translation |
|---|---|---|
| ampacity | ampacity | maximum current a conductor can carry |
| branch circuit | branch circuit | final circuit from breaker to outlets |
| feeder | feeder | supply circuit between panel and distribution |
| service entrance | service entrance | point where utility power enters |
| grounding electrode | grounding electrode | earth electrode (rod, plate) |
| bonding jumper | bonding jumper | equipotential bonding conductor |
| GFCI | GFCI | ground-fault circuit interrupter (RCD) |
| AFCI | AFCI | arc-fault circuit interrupter |
| raceway / conduit | raceway / conduit | piping or tray for wires |
| AWG | AWG | American Wire Gauge (wire size) |
| disconnect | disconnect | load-break switch at equipment |
NEC (National Electrical Code), officially NFPA 70, is the US national electrical installation code developed by NFPA. It is updated every 3 years (current edition — 2023). NEC is mandatory in most states and is the basis for many Latin American and Asian codes. Canada has a close code: CE Code (CSA C22.1).
The US household network is 120/240 V, 60 Hz, single-phase three-wire (split-phase): two 120 V hot legs to neutral and 240 V between them. Sockets follow NEMA: 5-15R (15 A, 125 V, grounded), 5-20R (20 A), 14-50R (50 A, for stoves and EV chargers). Wires are sized by AWG (the smaller the number, the thicker the wire).
A key NEC feature is the broad GFCI (Ground-Fault Circuit Interrupter, an RCD equivalent) requirement: bathrooms, kitchens, outdoors, garages, basements, near sinks (art. 210.8), tripping at 4–6 mA. The second unique device is AFCI (Arc-Fault Circuit Interrupter): arc-fault protection mandatory for bedrooms and most dwelling circuits (art. 210.12). Both are built into breakers or receptacles.
Ampacity follows NEC tables (Table 310.16 for copper/aluminium at 60/75/90 °C). Installation rules: NM cables (Romex®) in dry locations, metal conduit (EMT/RMC) and raceways elsewhere; grounding and bonding per art. 250 (grounding electrode, bonding jumper).
| Parameter | NEC (US) | PUE (RF) |
|---|---|---|
| Household voltage | 120/240 V, 60 Hz | 230/400 V, 50 Hz |
| Conductor sizes | AWG (12 AWG ≈ 3.31 mm²) | mm² (1.5, 2.5, 4…) |
| Socket protection | GFCI + AFCI | RCD 30 mA |
| Receptacles | NEMA 5-15R | Type C/F |
| Update cycle | 3 years | Chapter by chapter |
NEC-based rules apply in the USA (NFPA 70), many Latin American states (Mexico NOM-001-SEDE, Colombia NTC 2050, Peru CNE), the Philippines (PEC), several Caribbean and Middle East countries. Canada uses its own CE Code (CSA C22.1), structurally close to NEC.
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Reference · World electrical installation rules