Copper building wire

Guides for this category

• NM-B wire size by circuit: 15 to 60 amp breakers

  Which NM-B gauge goes on which breaker, why NM-B uses the 60 C column of NEC Table 310.16, and when to size up for distance or heat.

• THHN vs XHHW-2: which building wire to pull

  THHN/THWN-2 and XHHW-2 compared: insulation, wet ratings, pulling, conduit fill and where each one belongs, with the NEC tables behind them.

• UF-B vs NM-B: indoor cable or underground cable

  How UF-B and NM-B differ in build, wet ratings and direct burial, the burial depths from NEC Table 300.5, and the mistakes inspectors flag.

• Aluminum vs copper feeders: sizing, cost and terminations

  Copper and aluminum feeder sizes side by side from the 75 C column, the 200 A service example, and how to terminate aluminum so it lasts.

• Voltage drop: a worked example with NEC Chapter 9, Table 8

  Calculate voltage drop by hand for a 150 ft, 16 A run, see how each wire size compares, and learn when moving to 240 V beats buying bigger wire.

• How to read the markings on a wire jacket

  What each part of a wire legend means: size, stranding, insulation type, voltage, listing, oil and sun ratings, file numbers and footage markers.

• Electrical wire color code: what the NEC requires and what is convention

  Neutral, ground and hot conductor colors under the NEC, the 120/208 V and 277/480 V conventions, re-marking large conductors and posting rules.

• Underground wire: which types to use and how deep to bury them

  UF-B, USE-2, URD and conductors in conduit for underground runs, with the minimum cover depths from NEC Table 300.5 and the rules around them.

• How much wire to order: a quick takeoff

  Measure the route, add the box and panel allowances from NEC 300.14, multiply by conductors, and decide between a cut and a full spool.

• MC vs AC cable: grounding, where each is allowed and fittings

  MC and AC armored cable compared under NEC Articles 330 and 320: the grounding path, the AC bonding strip, wet locations, support, fittings and cost.

• SER vs SEU cable: service entrance or feeder

  SER and SEU compared under NEC Article 338: the bare or insulated neutral, when each may feed a subpanel, and sizing with 310.12 and Table 310.16.

• URD vs USE-2: cabled or single conductors for underground runs

  URD and USE-2 compared for direct burial: cabled versus single conductors, service laterals, neutral marking and the burial depths in NEC Table 300.5.

• PV wire vs USE-2: which conductor goes in a solar array

  PV wire and USE-2 compared under NEC 690.31: UL 4703 and 2 kV ratings, sunlight resistance, functionally grounded arrays and the rules by NEC edition.