| Wire | Ampacity | Voltage drop |
|---|
| One way | Wire | Voltage drop |
|---|
Conductors and short-circuit protection are sized from the table full-load current, not the nameplate (430.6(A)(1)). Overloads use the nameplate full-load current (430.6(A)(2)). Single motors, continuous duty.
Adds the circuit conductors at that size and an equipment grounding conductor sized from Table 250.122 for the conductor's 75°C ampacity.
Count every conductor in the raceway, including grounded and equipment grounding conductors (Ch. 9 Note 3).
Copper, Table 310.16. Not more than three current-carrying conductors, 86°F (30°C) ambient. Tap a row to select it.
| Size | 60°C | 75°C | 90°C | Breaker |
|---|
Only where the volume is marked or listed in Table 314.16(A) (314.16(A)(1)).
Each conductor that terminates or is spliced in the box counts once. A conductor that passes through unbroken counts once; a loop at least twice the free-conductor length in 300.16 (12 in.) counts twice (314.16(B)(1)). Don't count equipment grounding conductors here.
Enter inches as decimals or fractions: 6.5, 6 1/2, or 6-1/2.
Uses Chapter 9 Table 8 conductor resistance at 75°C and power factor 1. For large conductors on AC with a low power factor, Table 9 impedance gives a slightly higher drop.
Leave a box at 0 or blank when it doesn't apply. Inches over 12 are fine.
Transformers 1000 V and less (450.5(B)). Size the conductors with Wire size; secondary conductor length and protection follow 240.21(C).
Enter any two values. The other two fill in.
Efficiency is used only for horsepower. For sizing motor conductors and protection, use the table currents in Motor circuit, not this conversion (430.6(A)(1)).
TIA-598 color order. Buffer tubes, fibers, and ribbons all use the same 12-color sequence.
Enter a fiber number to see which buffer tube it's in and its color. The drawing outlines that tube and that fiber.
The letters printed on the jacket tell you where the cable is allowed. N = nonconductive (no metal). C = conductive (has metal strength members or armor).
Allowed anywhere, including plenum spaces above ceilings used for air return.
Vertical runs between floors and general areas. In a plenum only in metal raceway or a covered solid-bottom metal tray.
General areas on one floor. In a plenum only in metal raceway or a covered solid-bottom metal tray. In a riser only in metal raceway or a fireproof shaft.
| Pin | T568A | T568B |
|---|
Common questions on the job and at inspection, with 2026 NEC section numbers. Tap a question to open it.
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Prototype built on 2026 NEC rules (load calculations now live in Article 120). Check which code edition and local amendments your area enforces. Motors, air-conditioning and refrigeration equipment sized by nameplate minimum circuit ampacity and maximum overcurrent protective device, and welders have their own sizing rules and aren't covered here. Values are calculated from the code rules; always confirm with the code book and the authority having jurisdiction.
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Last updated November 3, 2026.