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    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, they actually are cycling in opposition over a single phase. 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?”


While we hope you find this series of articles about home inspection helpful, they should not be considered an alternative to an actual home inspection by a local inspector. Also, construction standards vary in different parts of the country and it is possible that important issues related to your area may not be covered here.
© McGarry and Madsen Inspection


More blogs about electrical service and distribution:

  1. How come my generator hookup got tagged as defective by the home inspector?

  2. Is the electric panel big enough for this house?

  3. How do the new tamper-resistant electric receptacles work?

  4. The electric panel is marked “Trilliant” and it’s all grey plastic. Is it alright?

  5. Why do you pay so much attention to electrical safety?

  6. What is the life expectancy of a circuit breaker?

  7. How dangerous is old electrical wiring?

  8. What is the right electric wire size for a home?

  9. Why does the electric company want my house electric system inspected before turning the power back on?

  10. What is a double tap at a circuit breaker?

  11. Why does that wall plug have push-buttons in the middle?

  12. Does this place have one of those “bad” electric panels I’ve heard about?

  13. My bathroom electric receptacle/outlet is dead, and there is no tripped breaker in the electric panel. What’s wrong?

  14. What is the switch on the wall with only two pushbuttons for?

  15. What are those strange looking wall switches in houses from the 1950s and 1960s?

  16. What is a lock device on a circuit breaker for?

  17. Can multiple neutral or ground wires be secured under the same terminal in an electric panel?

  18. Why are Zinsco and Sylvania-Zinsco electric panels a problem?

  19. Can wiremold be used at an exterior location?

  20. What is the life expectancy of electrical wiring in a house?

  21. How can adding wood paneling or a wainscot create an electrical safety hazard?

  22. What are the most common electrical defects found in a home inspection?

  23. Why is an old fuse panel dangerous?

  24. What does it mean when a wire is “overstripped” at a circuit breaker?

  25. What is the difference between “grounded” and “grounding” electrical conductors?

  26. What is the difference between a Combination Arc Fault Circuit Interrupter (CAFCI) and an Arc Fault Circuit Interrupter (AFCI) circuit breaker?

  27. How can I tell if a receptacle/outlet is tamper resistant?

  28. What is a Dual Function Circuit Interrupter (DFCI)?

  29. Will a GFCI receptacle that is not grounded still function properly?

  30. Does a home inspector remove the electric panel cover plate and examine the inside of the panel?

  31. Can an electric panel be located over stairs?

  32. What are the code requirements for NM-cable (nonmetallic-sheathed cable or Romex®) in an attic?

  33. How do I trace and identify each circuit breaker in my electric panel to make a circuit directory?

  34. Why are extension cords dangerous?

  35. What problems does having too many electrical outlets on a single circuit cause?

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

  37. What happens when you press the “TEST” button on a circuit breaker in an electric panel?

  38. How many electric receptacles (outlets) are required in a hallway?

  39. Why does painting an electric receptacle (outlet) make it unsafe?

  40. Why are old electrical systems not always “grandfathered” as acceptable by home inspectors?

  41. Why do the lights dim when the air conditioner turns on?

  42. Where are GFCI receptacle outlets required?

  43. When were GFCI receptacle outlets first required?

  44. What is the height requirement for an electric receptacle outlet?

  45. Why are some electric receptacle outlets upside down (ground slot up) in a house?

  46. What is a “backstab” receptacle outlet?

  47. What electrical hazards does a Ground Fault Circuit interrupter NOT protect against?

  48. What does “listed” and “labeled” mean for an electrical component?

  49. Can an NM-cable be used to make a cord and plug to connect an appliance?

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

  51. What is the building code requirement for receptacle outlets at stairs and stair landings?

  52. Can a home surge protector be installed loose in the bottom of an electric panel box?

  53. Can a bare bulb “lampholder” light fixture be installed outdoors?

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

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

  56. What is the difference between an electrical receptacle, an outlet, and a plug?

  57. Should I buy a house near a high-voltage power line?