Which of the following three-phase electrical distribution systems is grounded?

In electrical distribution systems, grounding is crucial for safety, as it helps prevent electrical shock and equipment damage. The correct choice identifies both the 120/208-volt and 277/480-volt systems as grounded because these configurations include a neutral wire that is typically grounded.

The 120/208-volt system consists of a wye-connected transformer that provides a neutral point, which is grounded. This allows for the use of 120 volts for general lighting and receptacle circuits while still providing access to three-phase 208 volts for larger equipment.

Similarly, the 277/480-volt system also employs a grounded neutral in its wye configuration. This system is often utilized in commercial and industrial applications, where 277-volt lighting circuits can be used alongside 480-volt three-phase power for heavy machinery.

In contrast, the 480-volt, three-phase, three-wire system lacks a neutral and, as a result, does not provide a grounding mechanism in the same way. This type of system may still have grounding considerations, but it does not include a grounded neutral as part of its design, making it less versatile and safer for certain applications compared to the others mentioned.

Thus, identifying both the 120/208-volt and