What do junction boxes contain?

Junction boxes primarily contain electrical connections between different wires and circuits. While the correct answer points to GFCI (Ground Fault Circuit Interrupter), the function of these devices is to protect against electrical shock by cutting off power if a ground fault is detected. Junction boxes typically house various safety and functional components to manage the distribution and protection of electrical circuits, including but not limited to GFCIs.

The other options involve components that may not be housed within a junction box itself. Circuit breakers are often located in service panels rather than junction boxes, while wiring diagrams illustrate connections and layouts but are not physical components contained within junctions. Voltage regulators, which adjust the voltage in electrical circuits, are also separate components that wouldn't normally be found inside a standard junction box. Therefore, the presence of GFCIs in junction boxes is significant for ensuring safety in electrical installations.