Heating, Ventilation, and Air Conditioning (HVAC ) Electrical Practice Test

What does the term "high leg" refer to in a three phase system?

1. A neutral wire

2. A phase conductor with a higher voltage

3. A ground conductor

4. An inductive load

The correct answer is: A phase conductor with a higher voltage

The term "high leg" in a three-phase system specifically refers to a phase conductor that has a higher voltage relative to the other phases in the system. This is often seen in a delta-wye configuration where one phase (often referred to as the "high leg") is derived from a center-tapped transformer. This high leg is typically at a higher voltage compared to the other two phases and is used in certain applications to provide a reliable supply of power, especially for single-phase loads that require a higher voltage. In practical terms, the high leg provides 240 volts when measured against the neutral (grounded), while the other two phases provide 120 volts against the neutral. This makes it critical for electrical installations to be aware of which leg is the high leg, as it can lead to improper installations if loads are connected inappropriately. Understanding the distinction of the high leg is vital for avoiding electrical hazards and ensuring the proper operation of equipment. Having knowledge about high leg conductors is essential for electricians and HVAC professionals to ensure safety and compliance with electrical codes.