A panelboard assembly for a harsh and/or hazardous environment is provided. The panelboard assembly includes a core assembly. The core assembly includes a main breaker assembly configured to be electrically connected to a power supply, and a branch breaker assembly electrically connected to the main breaker assembly and configured to be electrically connected to one or more loads, and a power distribution heatsink assembly. The power distribution heatsink assembly includes an electrically-conductive heatsink having a first end and an opposing second end, the first end electrically connected to the core assembly and an electrically-nonconductive isolator electrically insulating the heatsink.