An electrical unit with modular hardware structure in which more complex and unsafe portions of the device are restricted for access by a qualified electrician only, whereas safe areas are made accessible to a non-electrician user, such as a homeowner or a low expertise technician, to help diagnose issues and/or upgrade the functionality of the device without requiring the presence of a high expertise technician/electrician. The restricted portion includes a main Printed Circuit Board (PCB) that is selectively populated with certain circuit components and that contains electrical connections to enable the electrical unit to be operated in a number of different operating configurations depending on which components are populating the main PCB. A smaller, interconnect PCB also may be provided in the restricted portion and hardware-paired with the main PCB to facilitate wiring of the main PCB via the interconnect PCB and add further modularity to the electrical interconnect scheme.