Which of the following options is a limitation for wiring in a plenum space?

Wiring in a plenum space requires consideration of safety and fire prevention. The correct response highlights that materials used in these areas must have low heat release properties. This is crucial because plenum spaces often serve as air circulation pathways for heating and air conditioning systems. If materials have high heat release or are more flammable, they can contribute to the rapid spread of fire and produce harmful smoke that can circulate throughout a building, compromising safety.

The regulations are designed to minimize fire risk in these environments, thereby protecting occupants and property. This characteristic is often defined in building codes and fire safety regulations to ensure that any wiring installed does not pose unnecessary hazards.

The other options do not accurately reflect the constraints placed on wiring installed in plenum spaces. Flexible conduits may be allowed, but they are not a strict requirement, and any type of material would pose a safety risk that is not permitted. Height restrictions are not generally a standard limitation for wiring in these spaces.