Probable Effect Concentration Quotients (PECQS) Practice Test

The type of protection that is not suitable for service cables subject to physical damage is split knob and tube wiring. This system consists of insulated conductors run through a series of ceramic knobs and tubes, which were commonly used in older buildings. While it allows for the installation of electrical wiring, it does not provide adequate protection from physical damage, particularly in areas where the wiring may be exposed to impact or pressure.

In contrast, other types of protection like rigid metal conduit and plastic conduit offer robust safeguards against physical damage, suitable for environments where cables may be at risk. Flexible non-metallic conduit provides some level of protection as well, but it is primarily designed for areas where flexibility is necessary rather than heavy-duty physical protection. Hence, split knob and tube lacks the durability and protective shield needed for service cables in potentially hazardous locations.