Can you run a 100 amp subpanel off a 200 amp main panel?

You can run a 100 amp subpanel off a 200 amp main panel, and it is one of the most common jobs in residential work. A 100 amp double-pole breaker in the main feeds the sub through appropriately sized conductors.

You can even run more than one, or a 200 amp sub off a 200 amp main. Panel ratings are maximums, not allocations; what the NEC limits is the calculated load on the service, per Article 220.

In the subpanel, neutrals and grounds land on separate bars, with the bonding screw removed. That separation is the detail DIY installs miss most.

Feeder sizing follows the breaker: 100 amps typically means #3 copper or #1 aluminum.

The panel feeder wire size calculator sizes the run from main to sub with the article cited.