What Size Wire for a 60, 100 or 150 Amp Subpanel? Copper and Aluminum

A 100 amp subpanel needs 3 AWG copper or 1 AWG aluminum wire for the hot conductors, and a 60 amp subpanel needs 6 AWG copper. Those are the sizes from the 75°C column of the NEC ampacity table, which is what the terminals on most panels and breakers are rated for. A long run needs larger wire to keep the voltage drop down. The wire size calculator works out your own load and distance.

Feeder wire size by breaker

For a 240 volt single-phase feeder, at 75°C. The first column of each metal is the size for the ampacity, and the second the size needed for a 150 foot run with a 3% voltage drop:

The neutral and the ground

• Four wires to a subpanel. A subpanel feeder has two hots, a neutral and a separate ground. The neutral and the ground are kept apart in the subpanel.
• The neutral carries the unbalanced load. It can be the same size as the hots, and may be smaller when the load is mostly 240 volt, but it must meet the code minimums.
• The equipment ground is sized by the breaker (NEC Table 250.122): 10 AWG copper for 60 amps, 8 AWG for 100 amps and 6 AWG for 125 to 200 amps, or a size larger in aluminum.

Choosing copper or aluminum

• Aluminum costs less and weighs less, so it is common for larger feeders, but needs one or two sizes larger than copper for the same current.
• Use terminals and lugs rated for aluminum (marked AL or AL/CU), clean the wire, apply an anti-oxidant compound and tighten to the torque on the label.
• Only the feeder is aluminum: the branch circuits in the subpanel are usually copper.

Long runs and voltage drop

A 100 amp load 300 feet away on copper needs 2/0 AWG to keep the drop to 3%, against 3 AWG for a short run. Use the voltage drop calculator to check a longer run, and see the voltage drop chart.

Before you start

• Check that the main panel has room for the breaker and the load. A subpanel does not create capacity: the main panel and the service must carry the total.
• Buy the wire for a feeder in conduit as individual THHN or XHHW conductors, or as a cable listed for the use, and follow the local code on burial depth for an outbuilding.
• Get a permit and an inspection: it is the usual requirement for a new feeder and subpanel.
• Have a licensed electrician make the connections in the main panel.

These sizes are for the standard ampacity table and a typical installation, not for service conductors, which have their own rules. Your local code and your inspector decide.

Frequently asked questions