100 Amp Subpanel Feeder Size

Find the exact wire gauge you need for your specific electrical load.

Quick Answer

For a standard 100 Amp subpanel, the most common cost-effective choice is #1 Aluminum SER cable or individual XHHW conductors.

1Load Requirements

Total Load Amps

Load Duration

2Conductor Preferences

Material Preference

Insulation Rating (75°C vs 90°C)

Even if your wire is rated for 90°C (like THHN), you must usually size it based on the 75°C column because the breakers and lugs at the ends are only rated for 75°C.

Recommended Wire Size

NEC Table 310.16 →

-AWG

Ampacity (75C)-

Wire Diameter-

Load Requirement

Your load requires 100 Amps continuous

100 A

NEC 310.16 Lookup

Find smallest Aluminum wire @ 75C column

1 AWG

Wire Ampacity100 A

Physical Diameter0.289 inches

Safety Margin

The percentage of 'headroom' between your actual load and the wire's maximum capacity. A higher margin reduces heat and allows for future expansion.

0.0%

Popular wire wizard Configurations

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Ampacity Calculation

Wire size is selected by comparing the required ampacity (after continuous load adjustments) to the values in NEC Table 310.16, while ensuring the wire's temperature rating matches the termination rating (typically 75°C). Once selected, verify voltage drop with our [Voltage Drop Calculator](/tools/voltage-drop).

NEC 310.16 Allowable Ampacities

NEC Table 310.16 is the primary reference for conductor ampacity. It lists allowable currents for copper and aluminum conductors at different temperature ratings (60°C, 75°C, 90°C).

Frequently Asked Questions

What is the difference between 60°C, 75°C, and 90°C columns?

These columns represent the temperature rating of the wire insulation. However, you must typically use the 75°C column for terminations on breakers and devices, even if the wire is rated 90°C (like THHN).

Does THHN count as 90°C?

Yes, THHN is rated for 90°C in dry locations. This higher rating allows for derating adjustments, but the final ampacity is often limited to 75°C at the termination points.

When is a load considered continuous?

A load is continuous if it operates for maximum current for 3 hours or more. Continuous loads require the overcurrent device and conductors to be sized at 125% of the load.

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100 Amp Subpanel Feeder Size

Quick Answer

Understanding Wire Sizing

1Load Requirements

2Conductor Preferences

Recommended Wire Size

Load Requirement

NEC 310.16 Lookup

Popular wire wizard Configurations

Ampacity Calculation

NEC 310.16 Allowable Ampacities

Frequently Asked Questions

What is the difference between 60°C, 75°C, and 90°C columns?

Does THHN count as 90°C?

When is a load considered continuous?

100 Amp Subpanel Feeder Size

Quick Answer

Understanding Wire Sizing

1Load Requirements

2Conductor Preferences

Recommended Wire Size

Load Requirement

NEC 310.16 Lookup

Popular wire wizard Configurations

Ampacity Calculation

NEC 310.16 Allowable Ampacities

Frequently Asked Questions

What is the difference between 60°C, 75°C, and 90°C columns?

Does THHN count as 90°C?

When is a load considered continuous?