Final answer:
Equipment with voltages over 250 volts AC or DC should have a 'Caution' label visible at all times, to alert users to the high voltage and the potential electrical shock hazards, ensuring safety measures are adhered to.
Step-by-step explanation:
Equipment operating with voltages over 250 volts AC or DC needs to have safety labels that are clearly visible even when doors are open or when panels are removed. These safety labels are imperative to warn and protect individuals from electrical hazards associated with these high voltages. It is essential to understand that high voltages, whether AC or DC, can pose a greater risk of shock hazards as compared to low voltages, and precautions are necessary. Specifically, AC shocks can often be more harmful than DC shocks, which is why Thomas Edison initially promoted DC for power distribution.
Moreover, these labels ensure that there is an awareness of the presence of high voltage which can prevent serious and potentially fatal injuries. Electrical appliances, as well as protective systems like circuit breakers and three-wire systems, are designed to safeguard against thermal and shock hazards by preventing a person from coming into contact with live/hot wires. However, when working with or around such equipment, visible warning labels are a key safety feature.
Therefore, the label that must be attached and visible at all times on equipment with high voltages is a 'Caution' label, which signifies the presence of high voltage and the potential danger it represents, ensuring safety protocols are observed.