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When installing 100 amp electrical service, choosing the proper copper wire size is critical for safety and optimal system performance. This article provides an overview of standard 100a copper wire sizes used for various parts of a 100A installation.

Copper Wire Sizes for 100 Amp Electrical Circuits

Service Entrance Wires

For overhead and underground 100A service entrance conductors, the recommended 100a copper wire size is 3/0 AWG. This meets NEC minimum size requirements for a 100 amp service using copper wiring. The large diameter of 3/0 AWG enables safe passage of the full 100A current.

Feeder Wire Size

Where a 100A subpanel will be fed from the main panel, 3/0 AWG copper is the standard 100a copper wire size used. This properly sizes the 100A subpanel feeder wire based on the designed load in the subpanel. In some cases 1 AWG may be seen, but 3/0 AWG offers lower voltage drop.

Branch Circuit Wire Size

For branch circuits supplied through a 100A circuit breaker, the minimum 100a copper wire size is #3 AWG. This gauge meets NEC requirements for proper current carrying capacity on a 100 amp circuit. The thicker #3 wire prevents overheating from occurring on the branch circuit.

Ground Wire Size

The recommended 100a copper wire size for an effective grounding conductor at a 100A service size is #4 AWG. This satisfies NEC standards for proper grounding up to a 100 amp service. The thicker gauge enables the grounding system to quickly clear any faults.

THHN Wire Insulation

THHN is a common insulation type used on copper wires in conduit for 100A circuits. For example, a #3 THHN wire supports 100A breakers, while #10 THHN wires work for 30A branch circuits. THHN withstands the high temperatures that can occur in a 100A circuit.

Maintaining Ampacity

Using the standard 100a copper wire sizes like 3/0 AWG for service entrance conductors maintains the designed 100A ampacity rating. Properly sized wires prevent excessive heat buildup and damage from potential overload conditions.

Voltage Drop Effects

For long copper wire runs, upsizing one gauge size can help minimize voltage drop. For example, use 2 AWG rather than 3/0 AWG. Excessive voltage drop results in equipment problems, so keep wire distances within recommended limits.

Wire Splice Connections

When splicing 100A copper wires, choose connectors listed for that size and amperage. Many basic wire nuts only support #10 or #12 AWG wires. For the larger 3/0 AWG, specific 100A rated splicing products must be utilized.

Wire Lug Terminations

At the main service panel, use properly rated lugs for 3/0 AWG 100a copper wires. Standard lugs may only accept wires up to #4 AWG. Carefully match lug amp capacity and wire size range when terminating 100A service entrance conductors.


Understanding the standard 100a copper wire sizes for different 100A electrical circuits ensures proper current capacity, safety, and code compliance. Using the recommendations for 3/0 AWG service entrance, 3/0 AWG feeders, #3 AWG branch circuits, and #4 AWG grounding provides a robust 100A copper installation.

Published On: 2023年11月8日Categories: ,