What Wire Size Should You Use for a 100 Amp Aluminum Run?
When installing a new 100 amp electrical service or upgrading your main panel, one key decision is choosing the right size aluminum wire for the job. Using an aluminum conductor that's too small can lead to dangerous overheating and electrical fires. On the other hand, oversized wire wastes money and materials.
Our goal is to enable DIYers, homeowners, and electricians to understand the National Electrical Code requirements and select the optimal aluminum wire size. We'll provide clear guidelines and cable size recommendations based on expert analysis and real-world installations. With the right information, you can size your 100 amp aluminum feeds with total confidence.
Wire Sizing Basics
Key Factors in Choosing Wire Size
Several important criteria go into specifying the correct wire size for a 100 amp circuit:
- Desired ampacity rating - for a 100 amp service, choose a thickness rated for at least 100A.
- Length of wire run - longer distances require larger wires to minimize voltage drop.
- Ambient temperature - wires heat up easier in hot environments.
- Voltage drop limits - prevents inefficient power transmission.
- Cost considerations - thicker wires are more expensive.
Understanding Wire Gauges and Ampacity
Electrical wires are sized using the American Wire Gauge (AWG) system. The gauge corresponds to the wire's diameter, which in turn determines the maximum current capacity or ampacity. Thicker wires can handle more current. Ampacity tables provide the rated capacities for each AWG at various temperatures.
When comparing aluminum and copper wire, aluminum conductors must be one or two sizes larger to carry the same amperage as copper. This is due to aluminum's higher resistance per unit volume.
Recommended Aluminum Wire Size for 100 Amps
100 Amp Service Wire Size Options
Based on National Electrical Code guidelines and real-world performance data, the two recommended aluminum wire sizes for a 100 amp service are:
- 2/0 AWG aluminum wire
- 4/0 AWG aluminum wire
The 4/0 AWG option has a thicker diameter and can carry more current over longer distances. However, the 2/0 size costs less and fits more easily into conduits. Both sizes work well for 100 amp residential services under 50 feet.
Calculating Voltage Drop
Voltage drop increases as wire runs get longer. For wire sizing, you generally want to keep voltage drop under 3% to maintain efficient power transmission. Charts are available showing the percentage of drop for each AWG size over various distances. Use these to select a thickness that keeps voltage drop within acceptable limits.
Meeting Code Requirements
The National Electrical Code includes minimum size standards for branch circuits and service entrances. For aluminum, you need a minimum of #1 AWG for a 100A service entry cable. The 2/0 and 4/0 sizes we recommend exceed NEC minimums and offer safe operation with room to spare.
Proper Installation of Aluminum Wire
Using the Right Connections and Terminations
Making reliable connections is especially important with aluminum wire. The terminations must be rated for aluminum and installed properly to prevent oxidation and loose connections leading to overheating. Choose lugs and connectors approved for aluminum and follow manufacturer instructions closely.
Additional Safety Tips
To further ensure safe aluminum wire installations:
- Apply antioxidant paste to prevent corrosion.
- Maintain the minimum bending radius to avoid damage.
- Separate aluminum wiring from copper to prevent galvanic corrosion.
Frequently Asked Questions
Is aluminum wire safe for 100 amp residential service?
Yes, when properly sized and installed, aluminum wire is safe for 100 amp residential services. Pay special attention to using the right connections and avoiding copper contact.
Can I use a smaller size aluminum wire?
It's not recommended. Smaller aluminum sizes like #2 or #3 AWG cannot handle 100 amps for very long and present a fire risk over time. Stick with 2/0 or 4/0 AWG.
What if my wire run is longer than 50 feet?
For longer wire runs exceeding 50 feet, go up one size to 4/0 AWG aluminum to prevent excessive voltage drop over the extra distance.
When wiring your home or shop for 100 amps of power, choosing 2/0 or 4/0 AWG aluminum wire will provide safe and reliable service. Follow code guidelines on minimum size, calculate voltage drop, and properly install rated terminations. Take the time to size your aluminum conductors correctly, and you'll get years of top performance.