Which type of transformer is used to lower voltage to a safe level, typically 120 volts?

The type of transformer used to lower voltage to a safe level, typically 120 volts, is the potential transformer. Potential transformers are specifically designed to reduce high voltages to lower, manageable levels while maintaining the proportionate relationships necessary for accurate measurement and monitoring. This function is crucial in the electrical grid, where high voltages are common; these transformers ensure safety for both equipment and individuals by providing a lower, standard voltage for use in residential and commercial applications.

In the context of the other options, service transformers are often used to directly supply power to consumers but may not specifically denote the measurement applications typical of potential transformers. Current transformers, on the other hand, are designed to measure current and are not used primarily for voltage reduction. Distribution transformers, while they also step down voltages for distribution, may work with a range of voltages and are not exclusively focused on providing standard low voltage levels for safety. Thus, the potential transformer is the most precise choice for the function described in the question.