Consider a typical household evening with lights, television, air conditioning, oven, and microwave all operating simultaneously. These devices require substantial electrical current, with wires serving as the highways for power transmission. Undersized wiring resembles narrow lanes causing traffic congestion—manifested as voltage drops, overheating, and potential hazards. How then should professionals select proper wire gauges for 100-amp service to ensure reliable operation?

Selection involves evaluating multiple critical factors:

1. Conductor Material: Copper offers superior conductivity but higher cost; aluminum requires larger diameters for equivalent current capacity.
2. Wire Gauge (AWG): American Wire Gauge standards dictate diameter and current capacity. Lower AWG numbers indicate thicker wires with higher ampacity.
3. Insulation Type: Materials like THHN, XHHW, and UF-B determine temperature, moisture, and chemical resistance.
4. Installation Environment: Indoor, outdoor, or underground applications affect heat dissipation and corrosion resistance.
5. Circuit Length: Longer runs require larger gauges to mitigate voltage drop below 3% of supply voltage.
6. Safety Compliance: All selections must adhere to National Electrical Code (NEC) and local regulations.

Per NEC guidelines:

• Copper: 4 AWG (standard applications), 2 AWG (long-distance or low-voltage-drop requirements)
• Aluminum/Copper-Clad Aluminum: 2 AWG (short runs), 1 AWG (medium distances), 1/0 AWG (extended circuits)

Note: Conduit installations may require larger gauges to account for reduced heat dissipation.

Thermoplastic-insulated wiring for dry/damp indoor conduit installations. Cost-effective but unsuitable for direct burial or sunlight exposure.

Cross-linked polyethylene insulation excels in harsh environments. Suitable for conduit or direct burial with superior longevity.

Underground service entrance cable with sunlight and moisture resistance. Requires no additional protection when buried.

Service entrance cable connecting meters to panels. Permitted for indoor/outdoor exposed or concealed runs.

Underground feeder cable rated for burial without conduit. Also approved for wet locations.

Essential safety components must meet:

• 8 AWG copper
• 6 AWG aluminum

Ground wires require green insulation or bare copper with proper bonding to grounding electrodes.

• Moderate-sized residences with conventional appliances
• Detached garages or workshops
• Small commercial spaces (offices, retail)
• Construction site temporary power
• Subpanel feeders in larger buildings

The formula: Voltage Drop (V) = Current (A) × Length (ft) × Resistance (Ω/ft). Maintain voltage drop below 3% of supply voltage. Example: 100A load over 100ft using 4 AWG copper (0.249Ω/1000ft) yields 2.49V drop (1.04% of 240V supply)—within acceptable limits.

1. Use UL-listed dual-rated connectors
2. Apply antioxidant compound at terminations
3. Torque connections to manufacturer specifications
4. Schedule periodic inspections for oxidation

• Protect exposed wiring with conduit or armor
• Secure cables at approved intervals
• Maintain minimum bend radii
• Maintain clearance from heat sources
• Observe color-coding standards

Electrical modifications require licensed professionals. Always de-energize circuits before servicing and consult local authorities having jurisdiction.

This technical reference synthesizes code requirements and engineering best practices for 100-amp service design. Specifications may vary by jurisdiction—always verify with qualified electrical professionals.