An electrical panelboard enclosure includes an enclosure housing with an interior equipment chamber accessible by way of a service entrance door. A service panel is configured to receive power from a main power source. A main power breaker has a main power breaker toggle switch and is positionable between a power-on state and a power-off state to selectively activate and deactivate the main power. A power cutoff switch mechanism is operable from outside the service entrance door and is positionable between a power-on state and a power-off state to mechanically engage and deactivate the main power breaker toggle switch and cutoff the main power without opening the service entrance door. A lockout system is operable to prevent the service entrance door from being secured in a closed position unless the main power breaker and the power cutoff switch mechanism are in the same state.