How To Look At A House

McGarry and Madsen's home inspection blog for buyers of  

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What is the difference between single-phase and three-phase electric service?

Monday, January 27, 2020

Single phase electric service is what comes into virtually all homes. The service has two hot wires that are cycling through the same phase but in opposition, as shown in the diagram below. One leg produces 120-volt current and the two legs together produce 240-volt current because of the difference in the electrical potential between the two. It’s also worth noting that single-phase is a pulsating current, but three phase is not.  

    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 below 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.

    Also, 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 with answers to some Frequently Asked Questions (FAQ) about ELECTRICAL SERVICE:

What is the minimum overhead electric service drop height/clearance to a house?

 Why is a leaning electrical service mast dangerous? 

• What is the fireman’s switch emergency disconnect requirement for residential electrical service?

• What are typical copper service entrance wire/cable sizes for the electrical service to a house? 

What are typical aluminum service entrance wire/cable sizes for the electrical service to a house?

What is the minimum clearance of overhead electric service drop wires above a house roof? 

What is three phase electric service?

What does it mean when I find buried yellow "CAUTION" tape when digging a hole in the yard?

How can I find out the size of the electric service to a house?

What is the difference between the electric service to a mobile home and a site built home? 

What are the clearance requirements for an overhead electric service drop that is directly over or near a swimming pool?  

• What is the minimum size electric service to a mobile/manufactured home?

• Can anything else be attached to a service mast for overhead electric service besides the service cables? 

• What is the electrical "service point" of a house? 

Why is there a 3-phase breaker in a single phase panel with only two bus bars?

What is a service conductor?

• What is the minimum clearance under an electrical service drip loop of a house? 

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

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