Leave slots empty next to 100A breaker? I had an electrician come by yesterday to upgrade my service to 200A and to install a new 200A main panel with 100A subpanel (right next to it) so that I have a ton of slots and can isolate the entire second/third floors while i’m working up there. I am installing all of the breakers and branch circuits myself. He told me to leave the two slots open next to the 100A breaker in the main panel, but I don’t remember why. What is the reason for this? In general, I’ve found a lot of conflicting information about breaker placement in stack exchange/Mike Holt forums/etc.