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ENTER TO SEND · SHIFT+ENTER FOR NEW LINE · NEC 2023

53% 1 conductor

31% 2 conductors

40% 3+ conductors

NEC Ch.9 Table 1

Conduit Type

Conduit Size

Wire Type

Wire Size

# of Wires

CALCULATION RESULT

MAX CONDUCTORS (3+ WIRE, 40% FILL)

EMT

IMC

RMC

ENT

PVC Sch40

PVC Sch80

★ NEC Chapter 9, Tables 1, 4, 5. Values shown for 3+ conductors (40% fill). For 1 wire: 53% fill. For 2 wires: 31% fill. NYC follows NEC 2020 with NYCEC local amendments. Always verify with local AHJ.

Volume Each conductor = volume based on AWG (NEC 314.16(B)(1))

Devices Each device/switch = 2× largest wire

Clamps Internal clamps = 1× largest wire

NEC 314.16

Box Type

Wire Size (largest)

# Conductors

# Devices (switches/recepts)

Internal Clamps

Equipment Grounding Cond.

Extension Ring / Raised Cover

BOX FILL CALCULATION — NEC 314.16

CONDUCTOR VOLUME ALLOWANCES — NEC 314.16(B)

Wire Size	Volume per Conductor	Device Allowance (×2)	Clamp/EGC Allowance (×1)

BOX VOLUME REFERENCE — NEC TABLE 314.16(A)

Box Type	Volume (in³)	#14 AWG max	#12 AWG max	#10 AWG max

★ NEC 314.16(B) counting rules: (1) Each conductor entering box = 1 count. Conductors passing through = 1. Pigtails originating in box = 0. (2) Each device/strap = 2× largest conductor. (3) Internal cable clamps = 1× largest (regardless of count). (4) All EGCs = 1× largest EGC. (5) Fixture studs/hickeys = 1× largest conductor each.

310.16 Base ampacity from NEC Table 310.16

310.15(B) Temp correction factor

310.15(C) Bundling adjustment factor

NEC 310.15

Wire Size

Insulation Type

Conductor Material

Ambient Temp (°F)

Bundled Conductors (310.15(C))

Conduit in Sun (Rooftop)

AMPACITY CALCULATION — NEC 310.15

NEC TABLE 310.16 — ALLOWABLE AMPACITIES

Copper

Aluminum

Wire Size	60°C (TW/UF)	75°C (THW/THHW)	90°C (THHN/XHHW-2)	Typical Breaker

TEMP CORRECTION FACTORS — NEC TABLE 310.15(B)(1)

Ambient Temp	60°C insulation	75°C insulation	90°C insulation

BUNDLING ADJUSTMENT FACTORS — NEC 310.15(C)

# Current-Carrying Conductors	Adjustment Factor
1–3	None (1.00)
4–6	0.80
7–9	0.70
10–20	0.70
21–30	0.60
31–40	0.50
41+	0.45

★ NEC 310.16 — conductors in raceway, cable, or earth. Based on 60Hz, 3 or fewer current-carrying conductors, 30°C (86°F) ambient. Terminal temp rating: use 60°C column for equipment rated 60°C; use 75°C column for equipment rated 75°C (most panels/breakers). THHN/THWN-2 90°C rating used ONLY for derating calculations — terminals limit final ampacity to 60°C or 75°C column. Rooftop adder per NEC 310.15(B)(3)(c): add temp adder to ambient before applying correction factor. NYC follows NEC 2020 with NYCEC amendments.

3% NEC recommended max — branch circuits (210.19 FPN)

5% NEC recommended max — feeder + branch combined

VD Formula VD = (2 × K × I × L) / CM

NEC 210.19 / 215.2

Load (Amps)

One-Way Distance (feet)

System Voltage

Phase

Conductor Material

Max Voltage Drop %

VOLTAGE DROP CALCULATION

WIRE SIZE COMPARISON — ALL SIZES

Wire Size	CM Area	Voltage Drop	Drop %	Voltage at Load	Status

★ Formula: VD = (2 × K × I × L) / CM for single phase. VD = (1.732 × K × I × L) / CM for three phase. K = resistivity constant: Copper = 12.9, Aluminum = 21.2. CM = circular mils of conductor. L = one-way length in feet. NEC 210.19(A) Informational Note: voltage drop should not exceed 3% for branch circuits. NEC 215.2(A) Informational Note: combined feeder + branch circuit drop should not exceed 5%. These are recommendations, not code requirements — but good engineering practice.

Straight Length = 8× largest raceway — NEC 314.28(A)(1)

Angle/U Distance = 6× largest + sum of others in row — NEC 314.28(A)(2)

NEC 314.28

Pull Type

Largest Raceway (inches)

★ Only the LARGEST raceway matters.
You can have 5× 2" conduits going through — box length is still 8× the largest one.
Other raceway sizes do NOT add to the calculation.

        ★ NEC 314.28(A)(1): Straight pull — box length ≥ 8× largest raceway.

        ★ NEC 314.28(A)(2): Angle/U pull — distance from raceway entry to opposite wall ≥ 6× largest + sum of others in same row on same wall.

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