The correct answer is:
D. on high current switches or receptacles.
WHY:
Plastic faceplates should not be used on high current switches or receptacles (outlets) due to safety considerations. High current switches or receptacles are those that are designed to handle larger electrical loads, such as those found in circuits with heavy appliances or equipment.
Plastic faceplates may not be able to handle the heat generated by high electrical currents, which could lead to melting, warping, or even a risk of fire. In such cases, it is recommended to use faceplates made from more heat-resistant materials, such as metal, to ensure safe and reliable operation.
Therefore, option D is the correct answer as it highlights the limitation of using plastic faceplates in situations where high currents are involved.