In order to understand the operation of a circuit it is necessary to know the appropriate elements, ie the devices in the control panels. In large panels we have high capacity buses that can subject people to situations of risk. The operating circuits are divided into command and power motor frame sizes, allowing first the safety of the operator and secondly the automation of the circuit. Contactors are mechanically actuated, electromagnetically actuated devices and may be power or auxiliary contactors. A respectable factor to be observed in the use of contactors is the sparks produced by the impact during the switching of the contacts. This promotes the natural wear of the same, as well as consisting of risks to human health. The intensity of the sparks can be aggravated in humid environments and also with the intensity of electric current circulating in the panel.

The command button is mentioned when talking about connecting an electric motor, because the first element that comes to mind is a key to turn it on, however in the “industrial key” or button there is the return to the rest position through a spring. The understanding of this concept is fundamental to understand why the existence of a seal in the control circuit.