Pushbuttons and selectors: these are devices that are mainly used in industry, providing the user with control over the running and stopping of machinery. Pushbuttons consist of two buttons, one green for start and one red for stop. The selector switches are devices consisting of a rotating lever with several positions. There is also the possibility of choosing a selector switch with a key, for greater security. Emergency stop: Also commonly known as an emergency stop button, this is an interlocked pushbutton. With this device, the circuit to which it is connected is completely closed until the pushbutton is turned and returns to the initial position. Indicators and warning lights: these are used to provide some kind of information to the user of the machinery. They can be simple coloured lights to indicate whether it is running or stopped, or digits that show some data in real time, for example, the frequency of operation. Current transformer: this is a circular device with a hole in the middle through which the conductor passes, and the current flowing through it can be regulated. Analysers and meters: these are used for monitoring and displaying the data of an electrical installation, e.g. the zero discharge analyser-meter allows the non-pouring of electrical energy from a generating installation into the power supply network of the electricity company.