Final answer:
A lock-in plug or a safety device ensures that a tool cord does not accidentally separate from an extension cord during operation. These devices secure the connection between the cords to provide constant power and improve safety.
Step-by-step explanation:
A lock-in plug or a similar safety device will prevent an accidental separation of a tool cord from an extension cord during operation. These devices can either lock the two cords together or provide enough resistance so that they do not come apart easily during normal movement. Using such a device is good practice to ensure that power tools maintain a constant connection to the power source, which is necessary for safe and efficient operation. When choosing a lock-in plug or safety device, make sure it is compatible with the specific cords you are using and is rated for the electrical load required by your tool.