NEC Table 310.16 Subpanel SizingUpdated for 2026Commercial Grade

100-Amp Subpanel Feeder Wire Gauge & Conduit Sizing Calculator

Determine whether to use #4 Copper, #2 Copper, #1 Aluminum, or 2/0 Aluminum for a 100-amp subpanel based on distance, voltage drop, and conduit size.

Regional Market Calibration:Adjusts trade labor, concrete mix, and building codes to local city averages.

Popular Dimension Presets:

Raceway & Conductor Cross-Section (NEC Ch. 9)NEC 40% Max Fill Rule Enforced

Visual packing conforms to NEC Chapter 9 Table 1 physical space guidelines.

Project Dimensions & Material Inputs

Feeder Run Distance(ft)

Conductor Type

Wiring Method

Recommended 100A Feeder Wire

1 AWG Aluminum 4-Conductor Feed (2 Hot, 1 Neutral, 1 Ground)

Voltage Drop & Conduit Trade Size

2.50% Drop at 75' | 1-1/4" to 1-1/2" Conduit

Contractor Bill of Materials (BOM) Breakdown

Item / Material Spec	Quantity	Unit / Package	Installation Notes
Mobile Home Feeder or Quadruplex Wire (1 AWG Aluminum)	85	Feet	Contains 2 insulated phase conductors, full neutral & ground
100-Amp 240V Main Lug Subpanel with Separate Ground Bar	1	Panel	Ground and neutral MUST remain unbonded in subpanels per NEC 250.32
1-1/4-in Rigid Schedule 40 PVC Conduit	75	Feet	Conduit fill conforms to NEC Chapter 9 Table 1 40% rule
Two 5/8-in × 8-Ft Copper Ground Rods (if detached)	2	Rods	Spaced 6+ feet apart bonded with 6 AWG bare copper

Estimated Project Cost Range (DIY vs. Turnkey Contractor)

National Average

DIY Raw Materials Only

$618 – $908

Cost of raw lumber, concrete, shingles, wire, or stone without equipment rentals or labor.

Licensed Contractor Turnkey

$1,525 – $2,375

Full installation: permits, site prep, skilled trade labor, equipment, and structural warranty.

Estimated Sweat Equity

~$1,187

Average trade labor savings if executed as a skilled DIY homeowner project.

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NEC Feeder Ampacity & Circular Mil Selection

Rendering formula...

100A Subpanel Sizing Math for 75 Foot Feeder Run

NEC Table 310.16 75°C Base Ampacity: 100A continuous service rating.
Conductor Selection: Aluminum requires #1 AWG minimum (#1/0 for long runs).
Voltage Drop over 75 ft = 2.50% (Well within 3% NEC branch circuit guideline).
4-Wire Configuration: 2 Hot Feeder Legs (100A), 1 Insulated Neutral (100A), 1 Equipment Grounding Conductor.

Engineering Tip: In National Average, subpanels in detached outbuildings mandate a local grounding electrode system (two ground rods) and isolated neutral bar.

Quick Reference Sizing & Coverage Table

Standard commercial specifications and pre-calculated project benchmarks.

Pre-Calculated

Feeder Run Distance	Copper Wire Gauge	Aluminum Wire Gauge	Min. PVC Conduit Size	Installed Contractor Cost
25 – 60 ft (Indoor)	#3 AWG Copper	#1 AWG Aluminum	1-1/4" Schedule 40	$950 – $1,600
60 – 100 ft	#2 AWG Copper	1/0 AWG Aluminum	1-1/2" Schedule 40	$1,400 – $2,300
100 – 150 ft	#1 AWG Copper	2/0 AWG Aluminum	2" Schedule 40 PVC	$1,900 – $3,200
150 – 220 ft	1/0 AWG Copper	3/0 AWG Aluminum	2" Schedule 40 PVC	$2,600 – $4,400

NEC Article 250.32 Buildings or Structures Supplied by a Feeder

NEC 250.32 & Neutral Separation Mandate

Subpanels in detached buildings require 4 conductors (two hots, one insulated neutral, and one equipment ground). The green bonding screw must be discarded, the neutral bus must remain floating, and two 8-ft copper ground rods spaced 6 ft apart must be driven.

Frequently Asked Questions

What size wire do I need for a 100 amp subpanel?

For runs under 75 feet, you need #3 AWG Copper or #1 AWG Aluminum. For runs between 75 and 130 feet, upsize to #2 AWG Copper or 1/0 Aluminum to prevent voltage drop.

Is aluminum wire safe for a 100 amp subpanel?

Yes, modern AA-8000 series aluminum alloy feeder wire is completely safe and standard practice for 100A–200A feeders. Equipment terminals are rated AL9CU. Aluminum is roughly 1/3 the price of copper.

Do you bond the neutral and ground in a subpanel?

NO. Neutral and ground must NEVER be bonded in a subpanel. They must only be bonded at the primary main service disconnect. Bonding them in a subpanel creates dangerous parallel return current on ground wires.

What conduit size is required for 100A aluminum feeder wire?

Four individual conductors of #1 or 1/0 aluminum require a minimum 1-1/2 inch Schedule 40 PVC conduit or 1-1/4 inch EMT to satisfy the NEC 40% conduit fill rule.

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