In a typical distribution system, what voltage is supplied to a customer?

• A. Primary voltage
• B. Transmission voltage
• C. Secondary voltage
• D. Tertiary voltage

Answer: (C)

The voltage actually supplied to a customer is the service voltage on the transformer’s secondary winding. In a distribution system, power travels from the plant over high-voltage transmission lines, then through distribution feeders at a higher, but still lower than transmission, voltage on the primary side. A distribution transformer steps this down to a low voltage suitable for customer use, and that stepped-down voltage—the secondary—is what runs to the service entrance and into the building. For homes in the U.S., that secondary voltage is typically about 120/240 V. The other voltages describe levels on the network before or beyond the service (transmission voltage is the high long-distance voltage, primary voltage is the higher feeder voltage before stepping down, and tertiary voltage is used for specific internal equipment), none of which are the voltage supplied to the customer.