NEMA PB 1-2011

This standards publication covers single panelboards or groups of panel units suitable for assembly in the form of single panelboards, including buses, and with or without switches or automatic overload protective devices (fuses or circuit breakers), or both. These units are used in the distribution of electricity for light, heat, and power at 600 volts and less with:

a. 1600 ampere mains and less
b. 1200 ampere branch circuits and less