In the HVAC industry, equipment is commonly built to operate on either single phase or three phase electrical power. Technicians spec these options every day, but understanding the differences—and the advantages of each—helps ensure the correct equipment and installation decisions are made.
Electrical Phase Basics
Before diving into AC phases, it helps to understand how electrical current behaves in its simplest form.
No Phase: DC Power
A battery is an easy reference point for understanding DC (Direct Current). A battery has fixed positive and negative terminals—polarity. In a DC system:
- Electricity flows in one direction only
- Polarity never changes
This is the opposite of AC power, which constantly reverses direction.
Single Phase AC Power
Most homes and small businesses in North America are supplied with 120-volt, single phase, 60 Hz AC power.
With AC power:
- Polarity alternates 60 times per second
- Current changes