New York State Master Electrician Practice Exam

The correct choice is based on the requirements for safely supporting open conductors. In electrical installations, open conductors must be supported in a way that maintains their insulation and minimizes the risk of electrical hazards. Glass knobs, porcelain insulators, and metal racks have established uses in supporting open conductors properly. Glass knobs and porcelain insulators provide necessary insulation; they keep the conductors separated from surfaces where an electrical fault could occur. They also have the mechanical strength needed to support the weight of the conductors reliably over time. Metal racks, while conductive, can be utilized for supporting open conductors when proper insulation and other safety measures are applied. This is because the metal can be grounded, allowing for a safe dissipation of any stray electrical currents. On the other hand, plastic brackets, while non-conductive, may not offer the same level of support or stability needed for open conductors in various environmental conditions. They could be susceptible to degradation over time due to UV exposure or temperature variations, affecting their effectiveness and reliability in supporting electrical conductors. Therefore, the use of plastic brackets for this purpose is generally not permitted under safety standards for electrical installations.