Where are PCB's most commonly found?

PCBs, or polychlorinated biphenyls, are synthetic organic chemicals that were widely used in various industrial applications due to their chemical stability and insulating properties. One of the primary areas where PCBs were commonly found is in electrical transformers, particularly those manufactured before 1980 when their use was prevalent before regulations restricted them due to their environmental and health hazards.

Electrical transformers utilized PCBs as coolants and insulating fluids, making them integral to the operation of many types of electrical equipment. The manufacturing ban and regulations that came about in the late 1970s prompted the phase-out of PCBs, hence why older transformers, especially those created prior to this shift in the late 1970s, are significant sources of PCB contamination and exposure.

The other options, while they mention materials and components where PCBs were sometimes present, do not represent the primary context in which PCBs were used and thus are less accurate in addressing where PCBs are most commonly found.