Three phase is the way power is generated and transported over long distances by electric utilities. It is also the type of service to large commercial and industrial buildings. Three phase is converted to single phase (split-phase) by residential transformers, primarily because single phase is more suitable for residential power requirements for lighting and small appliances.

    The diagram above shows the wave pattern of each phase of one cycle of three phase power, with the vertical dimension being voltage and the horizontal representing time. Each phase is symmetrically 120º apart over a 360º cycle, and the elegance of this pattern is that it provides a continuously balanced flow of electricity, so that the sum of the three conductors is always zero. In other words, the voltage of one conductor at any point in time is balanced by the opposite voltage of the sum of the  other two conductors.

    If you took the black wave line in the diagram above and flipped it over the zero reference line below it, to create a mirrored opposing wave, the two lines would be a representation of single phase power. Although single phase has two hot wires and might seem like it should be called “two phase” power, the two wires are actually cycling in opposition over a single phase, as shown in the diagram below. The big difference between the two types of service is that single phase is a pulsating voltage. 

    Three phase power is extremely rare as a residential electrical service. Also, there are multiple variations of three phase service and understanding the difference between them gets very technical. But to learn how to tell what type of service a building has, see our blog post “What is a reliable way to tell if the electric service is 3 phase or single phase?”

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Here’s links to a collection of our other blog posts about ELECTRIC PANELS:

• What causes copper wires to turn green or black in an electric panel?  

• What is the maximum number of circuit breakers allowed in an electric panel?

• When should a corroded or damaged electric panel cabinet or disconnect box be replaced? 

• What is a tandem circuit breaker? 

• When did arc fault circuit interrupter (AFCI) breakers first become required?

• Can an electric panel be located in a closet? 

• Can an electric panel be located in a bathroom? 

• Can you add circuit breakers by different manufacturers to an electric panel if they fit?

• My circuit breaker won't reset. What's wrong?  

• What is a split bus electric panel?

• What is the difference between "grounded" and "grounding" electrical conductors? 

• What does it mean when a wire is "overstripped" at a circuit breaker?

• Why is an old fuse panel dangerous?  

• Who is the manufacturer of those "bad" electric panels?

• Why is the circuit breaker stuck in the middle? 

• What is a double tap at a circuit breaker?

• What is the right electric wire size for a circuit breaker in an electric panel?

• What is the life expectancy of a circuit breaker? 

• What is the maximum allowed height of a circuit breaker (OCPD) above the floor?

• What is the maximum height you can mount an electric panel above the floor? 

• What is the code required clearance in front of an electric panel?

• What is the main bonding jumper and where do it find it in an electric panel? 

   Visit our ELECTRIC PANELS page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.