See 60 Amp sub-panel image
Above image shows drawing of 60Amp sub-panel located next to main panel. Drawing shows #6 wire... 125' distance to garage calls for #4 wire. I ran #4 to my barn and have no problems.
Give thought to how many new breakers you want at garage.See photo of subpanel that holds three 240V breakersUsing drawing as a guide
. Replace existing 240Volt breaker with new 60 Amp breaker. Two hot wires connect to new 60 Amp breaker. Neutral connects to neutral busbar.More space
: You can free up space in main breaker box using a tandem breaker
. Or by doubling up 2 lightly used 120V circuits onto one breaker. Do not double-up on 240 BreakersConduit
: You want PVC conduit large enough to fit three #4 wires. Bigger conduit is easier to pull wires ... and maybe later ethernet wire, or alarm wire etc.Ground wire
: You can put a ground rod at garage and run #6 bare copper between sub-panel neutral-busbar and ground rod. Attach ground wire firmly with grounding clamp.I want you to check with local electrical supply for exact code
in your area concerning conduit requirements, grounding, and wire size. Tighten all lugs very tight against wire.