Final answer:
The usable space in an electrical box is considered reduced when a switch or receptacle is mounted on it, it contains two or more splice caps, or it contains fixture studs or hickeys; hence, all listed conditions apply.
Step-by-step explanation:
The question pertains to the factors that reduce the usable space inside an electrical box. The usable space in a box is considered reduced in the following scenarios:
- Switch or receptacle is mounted on it.
- The box contains two or more splice caps.
- The box contains fixture studs or hickeys.
Thus, the correct answer is all of the above. These are considerations taken into account by electricians and those studying electrical systems to ensure adherence to electrical codes and to maintain safety and functionality within the electrical system.