Here is a great diagram by Charles Buell @ Charles Buell Inspections: https://www.buellinspections.com/

I have heard it said that the development of our modern electrical system is the single greatest engineering achievement of mankind. While that is a bold statement, I find it difficult to conceive of technology that has more drastically changed our lives; stop for a minute and visualize life without electricity. Not only has our electrical grid revolutionized life on earth, but we have managed to do this in a remarkably safe way, especially in North America, where electricians are licensed and we have an electrical code through which we collectively enforce important minimum safety standards.

As a home inspector, I am constantly chasing the latest progress with building codes, standards, and technology. The average homeowner is often under the impression that there is one “code” way to build a house that is a black and white standard. Nothing could be farther from the truth. Residential construction is guided by building codes, electrical codes, fire codes, plumbing codes, energy codes, and then different building jurisdictions adopt different codes at different times and create local amendments to codes as they see fit. The codes are revised on 4-year cycles and are constantly chasing new technology and new understandings of what is “safe” with residential construction. The result is an evolving patchwork of standards that keeps any thoughtful builder, contractor or home inspector on their toes and presents endless opportunity for confusion and gray-area.

One of the more recent innovations with our electrical systems is AFCI protection. We have had GFCI protection for years, visualize the receptacles with the red and black re-set buttons on them. These have helped reduce the number for fatalities from electric shock and they have been a great success. The other hazard from electricity is fire and that is what the AFCI’s are designed to protect against. Arcing is when you get a hot luminous flash and electricity can create arcs that start fires. To protect against this, AFCI’s are designed to sense patterns on the sine wave and disable the electricity should it discover patterns that may be a result of arcing. Modern AFCI’s are called combination AFCI’s and they can protect against both series and parallel arcing.

Electrical Safety Repair
Amazing graph showing the success of GFCI protection. This is from the Electrical Safety Foundation International. 

Starting in 2014, arc fault protection started being required for most branch circuits in a house:  family rooms, dining rooms, living rooms, parlors, libraries, dens, bedrooms, sunrooms, recreation rooms, closets, hallways, bathrooms, and laundry rooms… just about everything except the garage and the exterior.

The most interesting part of this code change is that it requires that all receptacle outlets being installed or replaced, must now meet the modern AFCI requirements. This means, even if you own a 100-year old home and you are replacing or adding a receptacle or a circuit to one of these locations, the new wiring must meet modern AFCI requirements. This is the latest effort to keep us safe and could add some cost and complications to your wiring update projects. Below shows the code reference from the 2017 NEC.

 

406.4 (4) Arc-Fault Circuit-Interrupter Protection.  Where a receptacle outlet is located in any areas specified in 210.12 (A) or (B), a replacement receptacle at this outlet shall be one of the following:

    1. A listed outlet branch circuit type arc-fault circuit interrupter receptacle.
    2. A receptacle protected by a listed outlet branch circuit type arc-fault circuit interrupter type receptacle.
    3. A receptacle protected by a listed combination type arc-fault circuit interrupter type circuit breaker.