The safety of an antique electrical cord depends on a number of factors, such as its age, condition, composition and conductive capacity. Other factors include the device powered by the cord, whether it has a ground plug and whether it is UL approved.
The user should also examine the cord and assess whether it feels well matched to the appliance and how it compares to a cord used in recent years. Rubber, textiles and other materials that went into making the cord naturally deteriorate over time, and the passage of electricity through the wire creates heat that speeds up the deterioration of the materials. The older cord may have a two-prong circuit without the appropriate ground, which can cause shocks. There is also no way of telling whether the gauge of wire inside the cord is sufficient to carry the current without short circuiting it. Unless there is a legitimate reason for keeping the cord, there are too many risks associated with not changing it.