If a rubber blanket is rated for 20,000 volts and placed over a line hose also rated at that voltage, what is the insulating value of the combination?

The insulating value of a combination of two insulating materials, such as a rubber blanket and line hose rated for the same voltage, generally equals the rating of the individual components when they are used together. In this case, both the rubber blanket and the line hose are rated for 20,000 volts.

When these two materials are utilized in conjunction, they maintain their respective insulation ratings. Therefore, the insulating value of the combination matches the highest single rating of both components, which is 20,000 volts. This means that they can safely insulate against voltage levels up to that specified amount without a reduction in performance.

The other options reflect incorrect combinations or assumptions about increased insulating value that does not occur when identical rated items are combined. Only materials rated for higher voltages could potentially raise the combined value, which is not applicable here as both items share the same rating of 20,000 volts.