My shop is 20' x 20'. The main CB in my current panel says 150 so I assume I have 150Amp service. Otherwise no labels or markings clutters up the expanse of gray paint in the panel, so I guess my first job should be to map out the circuits I already have. And finally, the panel is full. No expansion possible. So I will have to put in a sub panel. I have room to put it right next to the existing panel. Unless that is a no no.