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Electrical Feeder Size Chart: Complete Guide 2026
Comprehensive NEC-compliant electrical feeder size charts with copper and aluminum ampacity tables, voltage drop calculations, and real-world installation examples for safe electrical work.
Electrical feeder sizing is one of the most critical calculations in any electrical installation, yet it’s often misunderstood even by experienced professionals. After working on hundreds of residential and commercial projects, I’ve seen firsthand how improper feeder sizing can lead to everything from nuisance breaker trips to serious safety hazards.
This comprehensive electrical feeder size chart combines NEC requirements with practical field experience to help you select the correct conductors for any application. The tables and guidelines below reflect the 2026 National Electrical Code requirements and include real-world factors that affect performance.
Whether you’re wiring a subpanel in a detached garage or sizing service entrance conductors for a new home, this guide provides the ampacity tables, calculation methods, and compliance checkpoints you need for safe, code-compliant installations.
Electrical Feeder: A set of conductors that distribute electrical power from the main service panel or disconnect to subpanels, distribution equipment, or major loads throughout a building.
Understanding Wire Gauge and Ampacity
Before diving into the feeder size charts, it’s essential to understand the fundamental concepts that determine conductor sizing. The American Wire Gauge (AWG) system can seem counterintuitive – smaller numbers indicate larger conductors, which seems backward until you understand the historical context of wire drawing.
Ampacity refers to the maximum current a conductor can carry continuously without exceeding its temperature rating. This isn’t just about the conductor size itself – it depends on multiple factors including insulation type, ambient temperature, installation conditions, and the specific NEC table being applied.
Copper vs Aluminum Conductors
The choice between copper and aluminum conductors significantly impacts your feeder sizing calculations. Copper conductors offer approximately 61% higher conductivity than aluminum of the same size, meaning you can often use a smaller AWG size with copper. However, aluminum’s lighter weight and lower cost make it attractive for larger feeders, especially in underground installations.
| Property | Copper | Aluminum |
|---|---|---|
| Conductivity (100% IACS) | 100% | 61% |
| Weight (per foot) | Heavier | Lighter (30% less) |
| Cost (per foot) | Higher | Lower (20-30% less) |
| Common Applications | Indoor feeders, branch circuits | Service entrances, underground feeders |
⏰ Pro Tip: When using aluminum conductors, ensure all connections are rated for aluminum and use antioxidant compound to prevent oxidation and ensure reliable connections.
Common Conductor Types
The insulation type determines the temperature rating and installation conditions for your feeder conductors. Here are the most common types you’ll encounter in feeder applications:
- THHN/THWN: 90°C dry location, 75°C wet location. Most common for indoor feeders in conduit.
- XHHW: 90°C dry, 75°C wet. Excellent moisture resistance and flexibility.
- SER Cable: Service entrance cable, typically 90°C rated. Used for service entrances and feeder installations.
- USE/RHH/RHW-2: Underground service entrance, 90°C rated. Designed for direct burial applications.
Comprehensive Feeder Sizing Tables
These feeder size charts are based on NEC Table 310.15(B)(16) for copper conductors and Table 310.15(B)(17) for aluminum conductors. All values assume not more than three current-carrying conductors in raceway, cable, or earth, and an ambient temperature of 86°F (30°C).
Copper Feeder Sizing Chart (90°C rated)
| AWG Size | Ampacity (90°C) | Typical Service/Application |
|---|---|---|
| 14 AWG | 25A | 15A circuits (derated to 80% = 20A) |
| 12 AWG | 30A | 20A circuits (derated to 80% = 24A) |
| 10 AWG | 40A | 30A circuits (derated to 80% = 32A) |
| 8 AWG | 55A | 40A circuits and small feeders |
| 6 AWG | 75A | 60A feeders and subpanels |
| 4 AWG | 95A | 70A feeders and subpanels |
| 3 AWG | 110A | 80A feeders and subpanels |
| 2 AWG | 130A | 100A feeders and subpanels |
| 1 AWG | 150A | 125A feeders and subpanels |
| 1/0 AWG | 170A | 150A feeders and service entrances |
| 2/0 AWG | 195A | 175A feeders and service entrances |
| 3/0 AWG | 225A | 200A feeders and service entrances |
| 4/0 AWG | 260A | 225A feeders and service entrances |
| 250 kcmil | 290A | 250A service entrances |
| 300 kcmil | 320A | 300A service entrances |
| 350 kcmil | 350A | 325A service entrances |
| 400 kcmil | 380A | 350A service entrances |
| 500 kcmil | 430A | 400A service entrances |
Aluminum Feeder Sizing Chart (90°C rated)
| AWG Size | Ampacity (90°C) | Typical Service/Application |
|---|---|---|
| 12 AWG | 25A | Not recommended for feeders |
| 10 AWG | 30A | Not recommended for feeders |
| 8 AWG | 40A | 30A circuits (derated to 80% = 24A) |
| 6 AWG | 50A | 40A feeders and subpanels |
| 4 AWG | 65A | 50A feeders and subpanels |
| 3 AWG | 75A | 60A feeders and subpanels |
| 2 AWG | 90A | 70A feeders and subpanels |
| 1 AWG | 100A | 80A feeders and subpanels |
| 1/0 AWG | 120A | 100A feeders and subpanels |
| 2/0 AWG | 135A | 125A feeders and service entrances |
| 3/0 AWG | 155A | 150A feeders and service entrances |
| 4/0 AWG | 180A | 175A feeders and service entrances |
| 250 kcmil | 205A | 200A feeders and service entrances |
| 300 kcmil | 230A | 225A feeders and service entrances |
| 350 kcmil | 250A | 250A service entrances |
| 400 kcmil | 280A | 275A service entrances |
| 500 kcmil | 315A | 300A service entrances |
Quick Reference: Common Service Sizes
| Service Size | Copper Required | Aluminum Required | Grounding Conductor |
|---|---|---|---|
| 60A | 4 AWG | 2 AWG | 8 AWG |
| 100A | 2 AWG | 1/0 AWG | 6 AWG |
| 125A | 1 AWG | 2/0 AWG | 4 AWG |
| 150A | 1/0 AWG | 3/0 AWG | 4 AWG |
| 175A | 2/0 AWG | 4/0 AWG | 2 AWG |
| 200A | 3/0 AWG | 250 kcmil | 2 AWG |
| 225A | 4/0 AWG | 300 kcmil | 1 AWG |
| 250A | 250 kcmil | 350 kcmil | 1/0 AWG |
| 300A | 300 kcmil | 500 kcmil | 1/0 AWG |
| 400A | 500 kcmil | 750 kcmil | 2/0 AWG |
✅ Important Note: The grounding conductor sizes shown are for copper. If using aluminum for the grounding conductor, increase the size by one AWG (e.g., use 4 AWG aluminum instead of 6 AWG copper).
Critical Factors Affecting Feeder Sizing
Simply selecting a conductor size from the tables above isn’t enough for code-compliant installations. Several critical factors must be considered to ensure safe and reliable operation of your electrical feeders.
Voltage Drop Calculations
Voltage drop becomes a significant concern with longer feeder runs. The NEC recommends limiting voltage drop to 3% for feeders and 5% total for feeders plus branch circuits. For long runs to outbuildings, detached garages, or remote equipment, you may need to upsize conductors beyond the minimum ampacity requirements.
Quick Summary: For copper conductors, use approximately 3/0 AWG for every 100 feet of 200 amp service run. For aluminum, use 250 kcmil for the same distance to maintain acceptable voltage drop.
“I’ve seen countless issues with voltage drop in feeder installations, especially for detached structures. A 200-foot run to a garage subpanel might require 4/0 copper instead of 3/0 just to maintain acceptable voltage levels.”
– Master Electrician, 20+ years experience
Continuous Load Requirements
NEC 210.19(A)(1) requires that continuous loads (operating for 3 hours or more) not exceed 80% of the conductor rating. This means you must size feeders for continuous loads at 125% of the load current. This rule commonly affects HVAC equipment, lighting circuits, and equipment that operates continuously.
Temperature Derating Factors
When ambient temperatures exceed 86°F (30°C), conductor ampacity must be derated according to NEC Table 310.15(B)(2)(a). Additionally, if more than three current-carrying conductors are installed in a raceway or cable, additional derating factors apply.
| Ambient Temperature | Derating Factor | Ambient Temperature | Derating Factor |
|---|---|---|---|
| 86-90°F | 0.91 | 114-118°F | 0.75 |
| 91-95°F | 0.88 | 119-122°F | 0.71 |
| 96-100°F | 0.84 | 123-128°F | 0.67 |
| 101-105°F | 0.82 | 129-134°F | 0.63 |
| 106-110°F | 0.80 | 135-140°F | 0.58 |
| 111-113°F | 0.76 | 141-149°F | 0.53 |
Conduit Fill and Installation Conditions
The number of conductors in conduit affects heat dissipation and therefore ampacity. When installing 4-6 current-carrying conductors, derate to 80%; for 7-9 conductors, derate to 70%; and for 10-20 conductors, derate to 50%. This becomes critical when installing multiple feeders in the same conduit.
NEC Compliance Requirements
Proper feeder sizing goes beyond ampacity calculations – it requires compliance with multiple NEC sections that work together to ensure safe electrical installations. Understanding these requirements helps avoid common inspection failures and safety issues.
Key NEC Sections for Feeder Sizing
- NEC 215.2 – Minimum Rating and Size: Feeders must have adequate ampacity for the calculated load and must not be smaller than 1/0 AWG copper for most dwelling unit applications.
- NEC 215.3 – Overcurrent Protection: Feeders must be protected by overcurrent devices rated no more than the ampacity of the conductors, with specific exceptions for certain applications.
- NEC 250.102 – Equipment Grounding Conductors: Requires properly sized grounding conductors for feeders based on the overcurrent protection rating.
- NEC 310.15 – Ampacity Tables: Provides the fundamental ampacity values that form the basis for all feeder sizing calculations.
- NEC 220 – Load Calculations: Specifies how to calculate the loads that determine the required feeder size.
Equipment Grounding Conductor Sizing
Every feeder requires a properly sized equipment grounding conductor. The size is determined by the rating of the overcurrent protective device, not the ampacity of the feeder conductors themselves.
| Overcurrent Device Rating | Copper Grounding Conductor | Aluminum Grounding Conductor |
|---|---|---|
| 15A | 14 AWG | 12 AWG |
| 20A | 12 AWG | 10 AWG |
| 30A | 10 AWG | 8 AWG |
| 40A | 10 AWG | 8 AWG |
| 60A | 8 AWG | 6 AWG |
| 100A | 6 AWG | 4 AWG |
| 200A | 4 AWG | 2 AWG |
| 400A | 2 AWG | 1/0 AWG |
⚠️ Important: Never omit the equipment grounding conductor from feeder installations. This is a common but dangerous practice that violates NEC requirements and creates serious safety hazards.
Common NEC Violations in Feeder Installations
After conducting thousands of inspections over the years, I’ve identified these recurring issues that lead to failed inspections and unsafe installations:
- Undersized conductors for continuous loads – Forgetting the 125% rule for loads operating 3+ hours
- Inadequate voltage drop consideration – Especially problematic for feeders over 100 feet
- Missing or undersized grounding conductors – A critical safety violation
- Improper derating for ambient temperature – Particularly common in attics and outdoor installations
- Conduit fill violations – Installing too many conductors without proper derating
- Wrong wire type for application – Using indoor-rated wire in wet locations
Real-World Feeder Sizing Examples
Let’s walk through practical scenarios that electricians and homeowners commonly encounter. These examples demonstrate how to apply the tables and NEC requirements in real installations.
Example 1: 100 Amp Subpanel in Detached Garage
Scenario: Installing a 100 amp subpanel in a detached garage 80 feet from the main panel. The garage will have basic lighting, outlets, and a small workshop area.
- Base ampacity requirement: 100A × 1.25 = 125A (for continuous load capacity)
- Minimum conductor size: 1 AWG copper or 2/0 AWG aluminum
- Voltage drop check: 80 feet is acceptable for standard sizing
- Recommended conductors: 1 AWG copper THHN or 2/0 AWG aluminum SER cable
- Grounding conductor: 6 AWG copper or 4 AWG aluminum
- Conduit sizing: Minimum 1-1/4″ for individual conductors, direct burial rated SER for underground
Example 2: 200 Amp Service Entrance
Scenario: New residential construction requiring a 200 amp service entrance with underground installation to the utility transformer 50 feet away.
- Base ampacity requirement: 200A × 1.25 = 250A
- Minimum conductor size: 3/0 AWG copper or 250 kcmil aluminum
- Voltage drop check: 50 feet is acceptable for standard sizing
- Recommended conductors: 3/0 AWG copper or 250 kcmil aluminum USE/RHH cable
- Grounding conductor: 2 AWG copper or 1 AWG aluminum
- Installation requirements: Direct burial rated cable with proper depth and protection
Example 3: 60 Amp Feeder for Workshop
Scenario: Feeding a workshop 120 feet away that will have a 5 HP air compressor and welding equipment (continuous operation expected).
- Base ampacity requirement: 60A × 1.25 = 75A (continuous load factor)
- Minimum conductor size from tables: 4 AWG copper or 2 AWG aluminum
- Voltage drop consideration: 120 feet requires upsizing – recommend 3 AWG copper or 1/0 AWG aluminum
- Recommended conductors: 3 AWG copper THHN in conduit or 1/0 AWG aluminum SER
- Grounding conductor: 8 AWG copper or 6 AWG aluminum
- Special considerations: Consider installing 2 AWG copper to provide extra capacity for future equipment additions
⏰ Time Saver: When in doubt between conductor sizes, always choose the larger size. The additional cost is minimal compared to the safety and reliability benefits, especially for feeders that are difficult to access once installed.
Common Installation Mistakes to Avoid
Based on field experience and inspection reports, these are the most frequent errors that lead to problems down the road:
- Undersizing for voltage drop – The most common mistake in feeder installations, especially for distances over 75 feet
- Ignoring continuous load requirements – Forgetting the 125% rule for equipment that runs continuously
- Wrong conduit fill calculations – Overcrowding conduits reduces heat dissipation and violates NEC requirements
- Improper conductor terminations – Especially critical with aluminum conductors, which require proper preparation
- Missing required bonding – Forgetting to bond metallic conduit or raceways at both ends
- Using wrong wire type – Installing indoor-rated wire in wet locations or using undersized SER cable
Frequently Asked Questions
How do I know what size feeder wire to use?
Start with your load calculation, then apply the NEC 125% rule for continuous loads. Select a conductor size from the ampacity tables that meets or exceeds this calculated value, then consider voltage drop for runs over 50 feet.
What size feeders do I need for a 200 amp service?
For a 200 amp service, you need at minimum 3/0 AWG copper or 250 kcmil aluminum conductors. Include a 2 AWG copper grounding conductor. Consider voltage drop for runs over 75 feet.
What size feeder for 100 amp service?
A 100 amp service requires minimum 2 AWG copper or 1/0 AWG aluminum conductors with a 6 AWG copper grounding conductor. For runs over 100 feet, consider upsizing to 1 AWG copper to reduce voltage drop.
How far can I run a 100 amp feeder without voltage drop problems?
For 100 amp service, you can typically run 2 AWG copper up to 100 feet without excessive voltage drop. Beyond this distance, you should upsize conductors – use 1 AWG for 150 feet or 1/0 AWG for 200 feet.
Do I need a separate grounding conductor for my feeder?
Yes, NEC 250.102 requires a properly sized equipment grounding conductor for all feeders. The size is based on the overcurrent protection rating, not the feeder conductor size.
What’s the difference between service entrance cable and feeder conductors?
Service entrance cable (SER) is designed for the main service connection and typically includes all required conductors in one cable. Feeder conductors are separate conductors used to distribute power from the main panel to subpanels.
Final Recommendations
After reviewing thousands of feeder installations and working with electrical professionals across the country, I can confidently say that proper feeder sizing is one of the most important aspects of electrical safety. The guidelines and tables in this comprehensive electrical feeder size chart provide the foundation for safe, code-compliant installations.
Remember that these tables provide minimum requirements – there’s nothing wrong with upsizing conductors for better performance, especially for longer runs or when future load growth is expected. The additional cost of larger conductors is minimal compared to the safety benefits and reduced voltage drop.
Always verify your local electrical code requirements, as some jurisdictions have amendments to the NEC that may affect feeder sizing requirements. When in doubt, consult with a licensed electrician or your local building official before proceeding with any electrical installation.
✅ Pro Tip: Keep a copy of these feeder sizing charts on your phone or in your truck. I still reference them regularly after 25 years in the trade – electrical work is one field where double-checking your calculations always pays off.