In a three-phase system, what is true about the voltage between any two ungrounded conductors?

In a three-phase system, the voltage between any two ungrounded conductors is a critical aspect to understand. The correct choice indicates that the voltage can indeed vary based on the configuration and specifics of the system, which makes option D accurate.

In three-phase systems, the line voltage is the voltage measured between two ungrounded conductors. This voltage is typically characterized as the difference in potential between these conductors. The actual value of this line voltage depends on the design of the electrical system, the voltage ratings involved, and any phase relationships.

The notion that the voltage can be influenced by the number of phases is valid in certain contexts, especially when systems are configured for different operational requirements. Furthermore, while many three-phase systems operate at 208, 240, 480 volts, or higher, it is not universally true that the voltage between any two ungrounded conductors is always going to be above 480 volts.

Thus, since the voltage can be equal to the line voltage and may vary, recognizing that it can take on numerous values led to the selection of D as the correct answer. This flexibility in voltage levels illustrates the diverse operating conditions and designs present in three-phase electrical systems.