When can a sub busway be joined to a busway without an overcurrent device?

The correct answer is that a sub busway can be joined to a busway without an overcurrent device when the sub busway is not near combustible materials. This condition is crucial because the presence of combustible materials can pose a fire hazard. If a fault were to occur in the sub busway, it could lead to overheating and potentially ignite nearby materials. Therefore, to enhance safety and adhere to electrical code requirements, it is essential that sub busways be installed in a manner that does not compromise the integrity of nearby structures or materials.

In contrast, factors such as accessibility, load above 10 amperes, or approval by an electrician do not inherently mitigate the risks associated with connecting sub busways without overcurrent protection in the presence of combustible materials. These considerations, while important in other contexts, do not specifically address the safety concerns dictated by the proximity of combustible materials to electrical installations.