Which form of ungrounded system allows for a grounded conductor route?

The choice indicating that the ungrounded system must be bonded to the enclosure is correct because it highlights a critical safety principle in electrical installations. In systems that are classified as ungrounded, establishing a bonding connection to the enclosure is essential to ensure that if a fault occurs, there is a low-resistance path for fault currents to flow safely to the ground. This reduces the risk of electrical shock and equipment damage.

Bonding the grounded conductor route to the enclosure mitigates potential risks associated with floating voltages or induced currents, which could arise in an ungrounded system. By ensuring that the enclosure is bonded, any faults can be safely cleared by the protective devices, such as circuit breakers or fuses, thereby enhancing the overall safety and reliability of the electrical system.

In contrast, the other options do not accurately reflect how grounding and bonding should function within ungrounded systems. Some may suggest that an ungrounded system can operate without any bonding, which increases safety risks rather than mitigating them. Others might imply limited scenarios where bonding might occur, which isn't the standard practice for establishing effective grounding.