How to Choose the Correct Aluminum Wire Size for 100 Amps

When selecting the right size of aluminum wire for a 100 amp circuit, the first thing to understand is the concept of "ampacity". Ampacity refers to the maximum amount of electric current a conductor can continuously carry before overheating. Exceeding the ampacity can cause the wire's insulation to melt or degrade over time.

Every wire gauge has an established ampacity rating that depends on factors like material composition, insulation type, and ambient temperature. Aluminum wiring is rated slightly lower than copper due to having higher electrical resistance per foot. Ampacity tables provide the recommended maximum currents for different wire sizes.

Key Factors Affecting Wire Amp Capacity Limits

• Gauge/diameter - thicker wires can handle more current
• Conductor material - copper has higher ampacity than aluminum
• Temperature - ampacity decreases as temperature increases
• Insulation type - some types limit max permissible current
• Number of current carrying conductors - more wires means higher ambient temps

Determining Necessary Current Capacity for a 100 Amp Circuit

In electrical systems, the term "100 amp" refers to the size of the overcurrent protective device (i.e. circuit breaker) installed at the supply end of the circuit. This 100 amp breaker is designed to trip and shut off power if current exceeds 100 amps, preventing conductor overloads.

To choose the right aluminum wire size for a 100 amp circuit, you need an aluminum gauge with an ampacity rating of at least 100 amps. In fact, an extra margin of 20-30% is recommended. So for 100 amp service, you would want an aluminum wire size rated for continuous currents of 120-130 amps.

Recommended Aluminum Wire Sizes for 100 Amp Circuits

According to ampacity tables, here are typical aluminum wire sizes used for 100 amp circuits:

• 1 AWG aluminum - rated for 130A
• 2 AWG aluminum - rated for 110A
• 3 AWG aluminum - rated for 95A (too small for 100A)

So 1 AWG or 2 AWG would be suitable aluminum conductors for a 100 amp circuit breaker.

Choosing Aluminum Wire Size for 100 Amp Breakers

The first step is using the correct wire size based on your 100 amp circuit breaker rating. Remember that wire gauge gets smaller as the AWG number gets larger. So a 1 AWG aluminum wire has a thicker diameter than 2 AWG.

Here are the key wire sizing guidelines to follow:

• Minimum 1 AWG aluminum wire for a 100A breaker
• Can also use thicker 0 AWG or 00 AWG aluminum
• 2 AWG aluminum is borderline too small
• Don't use thinner gauges like 3 AWG or 4 AWG

Referencing Ampacity Tables to Select Suitable Wire Diameter

Besides the above recommendations, you can independently determine the right aluminum wire size for a 100 amp circuit based on ampacity tables like the one below:

To fulfill the 100 amp service requirement, choose a wire gauge rating higher than 100 amps - indicating either 1 AWG or 2 AWG aluminum conductors.

Installation Tips for Aluminum Wiring at 100 Amps

When installing aluminum wires for 100 amp circuits, follow these guidelines to ensure safety and code compliance:

Special Precautions for Terminating Aluminum Conductors

• Use oxide inhibiting paste at connections
• Allow some slack to avoid expansion/contraction
• Apply 30% less torque than with copper wires
• Use larger terminals sized for aluminum

Sizing Connectors Properly for 100A Aluminum Wires

For 1/0 AWG or 2/0 AWG aluminum at 100 amps, use connector sizes of 1/0 AWG or larger. Avoid terminals rated for smaller 3 AWG copper, which can lead to overheating issues over time.

Adhering to Electrical Code Requirements

When running aluminum wires, follow NEC guidelines like:

• Use larger conduit (3/4-inch+) to ease wire pulls
• De-rate ampacity for number of current-carrying conductors
• Allow aluminum wires only on supply side of service disconnect

Common Sizes of Aluminum Wire for 100 Amp Service

The most popular choices of aluminum wire for 100 amp residential or commercial services are:

• 1 AWG - Offers 30+ amps extra capacity. Used for long wire runs.
• 2 AWG - Marginally rated for 100 amps. Lowest cost option.
• 1/0 or 2/0 AWG - Oversized wires better suited for high-demand loads.

Adjusting Wire Size for Temperature and Number of Conductors

Note that the wire size may need to increased beyond the above typical gauges if:

• There are over 3 current-carrying conductors in the conduit (limit is 4)
• Ambient temperature is above 30degC
• Length requires thicker wires to minimize voltage drop

Sample Wire Size Calculation for 100 Amp Circuit

As an example, for a 100 amp circuit with 2 AWG aluminum wires that has 4 current-carrying conductors in a conduit with 35degC temperature, the adjusted wire size using NEC de-rating factors would be:

2 AWG rated for 110A (from table)

De-rated to 83A (due to 4 conductors in conduit)

Further de-rated to 75A (due ambient max. temperature)

So we would need to choose a thicker 1 AWG aluminum wire due to all the de-rating factors bringing the 2 AWG below the desired 100 amp capacity.

Inspecting and Maintaining 100 Amp Aluminum Feeders

To keep your 100 amp aluminum wire feeds performing safely, annual inspections are recommended covering:

Checking Connections Have No Corrosion or Looseness

• Look for discolored, pitted or burned terminals
• Test tightness of connections and re-torque if loose
• Clean any corrosion with wire brush; reapply oxide inhibitor

• De-energize circuit before attempting any maintenance
• Wear PPE - insulated gloves designed for electrical work
• Use aluminum-rated tools to avoid damaging conductors

By selecting the right aluminum wire size for 100 amps and properly installing, terminating and maintaining the conductors, you can reap the benefits of aluminum in terms of lower material cost and reasonable longevity compared to alternatives like copper.