A hammer drill comprising: a motor; an electrical power circuit (100, 114, 106, 108) for providing power to the motor; a tool holder capable of holding a cutting tool; a drive transmission, capable of operating in at least two modes of operation (14, 16, 18), which, when a cutting tool is held by the tool holder, is capable of converting the drive output of the motor into a rotary drive for the cutting tool and/or repetitive impacts which are imparted to the cutting tool depending on the mode of operation of the drive transmission; a mode change mechanism which is capable of switching the drive transmission between the at least two modes of operation (14, 16, 18); at least one electrical switch (22, 52) located within the electrical power circuit (100, 114, 106, 108) for providing power to the motor which, when closed, is capable of providing power to the motor and when open, prevents power being provided to the motor; and a lock on mechanism which, when activated, locks the at least one switch in its closed state; a controller which is capable of controlling the operation of the motor; an electrical power circuit (100, 102, 104, 106, 108) for providing power to controller; wherein the motor is prevented from operating when no power is provided to the controller; characterised in that two power switches (110, 112) are provided within the electrical power circuit (100, 102, 104, 106, 108) for the controller which are located in parallel with each other within the circuit (100, 102, 104, 106, 108); in that the first power switch is connected to the mode change mechanism, is open when the drive transmission is operating in at least one of the modes of operation (14, 16, 18) and is closed when the drive transmission is operating in the other modes of operation; and in that the second power switch is connected to the lock on mechanism and which is arranged to be open when the lock on mechanism has been activated and closed when the lock on mechanism is de-activated. a motor; an electrical power circuit (100, 114, 106, 108) for providing power to the motor; a tool holder capable of holding a cutting tool; a drive transmission, capable of operating in at least two modes of operation (14, 16, 18), which, when a cutting tool is held by the tool holder, is capable of converting the drive output of the motor into a rotary drive for the cutting tool and/or repetitive impacts which are imparted to the cutting tool depending on the mode of operation of the drive transmission; a mode change mechanism which is capable of switching the drive transmission between the at least two modes of operation (14, 16, 18); at least one electrical switch (22, 52) located within the electrical power circuit (100, 114, 106, 108) for providing power to the motor which, when closed, is capable of providing power to the motor and when open, prevents power being provided to the motor; and a lock on mechanism which, when activated, locks the at least one switch in its closed state; a controller which is capable of controlling the operation of the motor; an electrical power circuit (100, 102, 104, 106, 108) for providing power to controller; wherein the motor is prevented from operating when no power is provided to the controller; characterised in that two power switches (110, 112) are provided within the electrical power circuit (100, 102, 104, 106, 108) for the controller which are located in parallel with each other within the circuit (100, 102, 104, 106, 108); in that the first power switch is connected to the mode change mechanism, is open when the drive transmission is operating in at least one of the modes of operation (14, 16, 18) and is closed when the drive transmission is operating in the other modes of operation; and in that the second power switch is connected to the lock on mechanism and which is arranged to be open when the lock on mechanism has been activated and closed when the lock on mechanism is de-activated.