Master Electrician Practice Exam

For a commercial building using a transformer, what voltage is the secondary side typically rated at?

1. 120 volts

2. 240 volts

3. 277 volts

4. 480 volts

The correct answer is: 120 volts

The secondary side of a transformer in a commercial building is typically rated at 277 volts when the primary voltage is 480 volts. This setup is common in commercial settings where lighting circuits are often powered by 277 volts due to energy efficiency and better voltage drop characteristics. In commercial electrical systems, 277 volts is preferred for lighting because it allows for longer runs of lighting circuits with less voltage drop compared to lower voltage systems. This is particularly useful in larger spaces where the distance from the transformer to the lighting fixtures can be significant. While 120 volts is commonly found in residential loads for outlets and small appliances, it is generally not the standard for secondary transformer outputs in commercial applications, as it does not accommodate the higher power requirements and efficiency needs of commercial lighting systems. Thus, although 120 volts is a common voltage, it does not match the common practice for commercial buildings that typically utilize the higher voltages like 277 volts for lighting.