A consumer unit is the main place for controlling a home or business electrical supply. They are found where the electricity supply enters the property and are a unit that controls the entire power supply.
It is made up of main switches, residual current devices (RCD's) and circuit breakers and can be manually or automatically shut off to prevent your property from damage due to any electrical issue that may arise.
The main switch is the mechanism that controls the electricity supply to your home or business, this has to be switched on and off manually, isolating the consumer unit.
The RCD's and circuits are tripped automatically to prevent electric shock or personal injury. An example would be where a light or a fuse has blown. Circuit breakers or MCB's act very similarly, they turn off automatically to protect electrical circuits from damage, for example in instances of overload or overcurrent.