If the panel has multiple breakers (up to six) that are marked “MAIN,” then you are looking at a split-bus panel from the mid-20th century. All of the “MAIN” breakers must be shut off to disconnect power to the home and none of them reflect the rating of the electric service. There are two ways you can figure out the service rating of a split bus panel. One way is to look carefully at the paper manufacturer’s data plate on the inside of the panel door for the amperage rating of the panel, which will show the maximum service size it is rated for.

    But the paper may be missing and the rating might be more than the size of the service—which can only be verified by determining the size of the service wires inside the panel box. We do not recommend the you remove the dead front (cover panel) to examine the wiring, so leave this to an electrician. Here is a chart of the rating of a service based on wire size in AWG (American Wire Gauge). Lower numbers indicate a larger wire.

    To learn more about split bus electric panels, go to our blog post
”What is a split bus electric panel?”

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.
©2016 - McGarry and Madsen Inspection


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Welcome to our blog!
We want you to be an informed homebuyer, and each blog post is a question that we have answered for our friends and customers over the years. Hope they help you make a good choice for your next home.

More blog posts about electric service and distribution:

  1. What is the best emergency back-up generator for the power outage after a storm?

  2. How can I tell if the electric outlets are grounded?

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

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

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

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

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

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

  11. My circuit breaker won’t reset. What’s wrong?

  12. Is a bare bulb light in a closet alright?

  13. What is reversed polarity at an outlet/receptacle? Why is it dangerous?

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

  15. What is a “missing twistout” at an electric panel?

  16. Where are smoke alarms required to be located?

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

  18. How far apart should electric receptacle outlets be placed in a garage?

  19. Will the electric company remove branches rubbing against the overhead service lines to my home?

  20. What is the lock device on a circuit breaker for?

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

  22. Can wiremold be used at an exterior location?

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

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

  25. What is an open electrical splice?

  26. Why is an old fuse panel dangerous?

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

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

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

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

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

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

  33. What are the most common defects with over-the-range microwaves?

  34. Can an electric panel be located over stairs?

  35. Does a GFCI-receptacle that is not grounded still function properly?

  36. Is a house required to have outdoor electric outlets?

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

  38. How can I change a 240V circuit to a 120V circuit?

  39. Can old electric wiring go bad inside a wall?

  40. What could cause an extremely high electric bill?

  41. Why are extension cords dangerous?

  42. What problems does having too many electrical outlets in a single circuit cause?

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

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

  45. Why are electrical outlets and plugs polarized?

  46. Why are old electric components not always “grandfathered” as acceptable by home inspectors?

  47. What is the difference between GFCI and AFCI circuit breakers?

  48. What causes flickering or blinking lights in a house?

  49. Why is bundled wiring in an electric panel a defect?

  50. Why are some electric receptacles/outlets upside down (ground slot up) in a house?

  51. Why is undersize electric wiring in a house dangerous?

  52. Why is a fuse box an insurance problem for homebuyers?

  53. What is a “backstab” receptacle outlet?

  54. What electrical hazards does a Ground Fault Circuit Interrupter (GFCI) not protect against?

  55. What is the color code for NM cable (Romex®) sheathing?

  56. What are the right words for talking about a house electrical system?

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

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

  59. How far away should a sink be from an electric panel?

  60. What are the requirements for NM-cables entering an electric panel box?

  61. How can I tell if the electrical service is 3 phase or single phase?

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

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

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

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

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

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

  68. What is a “while-in-use” weatherproof electrical receptacle outlet cover?

  69. Why is it unsafe to bond neutral and ground wiring at subpanels?

  70. Are wall light switches required to be “up” for “on” and “down” for “off”?

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