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Selecting the proper wire size is crucial when installing or upgrading an electrical panel to 100 amps. This article provides guidance on choosing appropriate wire gauges for 100 amp panels under different service scenarios.

Wire Size Selection for 100 Amp Electrical Panels

100A Service Entrance Wires

For the main 100A service panel, the minimum recommended wire size is 3/0 AWG copper. This meets NEC requirements for sufficient ampacity at the 100A rating. A 3/0 AWG conductor enables safe delivery of the 100A current.

100A Feeder Wires

When installing a 100A subpanel fed from the main panel, the standard wire size is also 3/0 AWG copper. This properly sizes the subpanel feeder wire for the designed 100A load in the subpanel.

100A Branch Circuit Wires

For branch circuits supplied through a 100A circuit breaker, #3 AWG copper is the minimum wire size per NEC. The #3 AWG gauge can handle the 100A current to prevent overheating failures.

Ground Wires

An adequately sized ground wire for a 100A panel is #4 AWG copper. This gauge satisfies code requirements for effective grounding at this ampacity. The thicker wire improves fault clearing.

THHN Wire Insulation

THHN insulation is commonly used on copper wires in conduit for 100A panels. For example, #3 THHN wire supports 100A breaker circuits. THHN withstands high temperatures and wet/dry installations.

Conduit Size Factors

When running multiple large THHN wires through conduit, watch conduit fill percentage. A 1″ conduit may only fit 2-3 #3 THHN wires for 100A circuits. Upsizing conduit preserves fill limits.

Maintaining Ampacity

Using standard wire sizes like 3/0 AWG maintains the designed 100A ampacity rating. Correct sizes prevent overheating damage from overloaded circuits. Oversizing is unnecessary.

Voltage Drop Effects

For long wire runs, upsizing one gauge manages voltage drop. Excessive drop can affect equipment function, so keep distances within guidelines or upsize wires.

Wire Splice Connections

Choose splice connectors rated for the wire gauge and ampacity like 3/0 AWG 100A circuits. Many basic splices only support 10-12 AWG wires. Use proper 100A products.

Terminal Lugs

Use lugs rated for 3/0 AWG wires when terminating 100A service entrance or feeder conductors. Standard lugs may only go to #4 AWG. Match lug ratings to wire size.


Choosing the right wire size for 100A panels, circuits, and grounding ensures safety, performance, and code compliance. Consulting NEC guidelines provides standardized sizing for reliable 100A service.

Published On: 2023年11月8日Categories: ,