Elevator Mechanic Practice Exam

What phase do you test first when measuring 3 phase AC incoming voltage?

1. L1-L2

2. L2-L3

3. L3-N

4. N-E

The correct answer is: L1-L2

The correct approach to measuring three-phase AC incoming voltage typically starts with measuring line-to-line voltages because they provide insights into the system's balance and operation. Testing L1-L2 first helps determine the voltage drop across two phases, which is essential for assessing the overall health of the electrical supply. When you measure L1-L2, you can determine if there is a balanced load, which is critical for the proper functioning of three-phase systems. This allows you to identify potential issues such as phase imbalances that could lead to inefficient operation or damage to the equipment. Other tests, such as those involving line-to-neutral or neutral-to-earth measurements, provide valuable information but are typically conducted after confirming the line-to-line voltages. This stepwise approach is standard practice, as understanding the relationships between the phases early on helps in diagnosing any issues more effectively.