Final answer:
A transformer is used to step voltage down to lower levels before electricity reaches a home or office. It adjusts the high-transmission line voltages to the safer levels required for residential and commercial use.
Step-by-step explanation:
The device used to step voltage down to lower levels before it reaches a home or office is A. Transformer. Transformers are essential components in the transmission and distribution of electrical power. They work based on Faraday's law of induction and can either increase (step-up) or decrease (step-down) voltage levels. For example, electric power is usually generated at voltages greater than 10 kV and is transmitted at voltages between 120 kV and 700 kV to limit energy losses during long distances. Once near the consumption area, a step-down transformer is used to reduce that voltage to safer levels such as 120, 240, or 480 V for residential or commercial use. The primary voltage of a step-down transformer is higher than the secondary voltage, which allows the current to be adjusted for safe and efficient home use.