Electrical – what 2017 NEC code talks about knob and tube replacement

Knob and tube wiring uses two separate copper conductors, each isolated by cotton cloth or soft rubber. The conductors are strung tightly through the cavities of your walls and floors, and depend on being separated by air in order to avoid overheating. When going through joists, the wires pass through porcelain tubes. In the wall and floor cavities, they are attached intermittently by porcelain knobs.

Knob and tube wiring was commonly used in North America from the 1880s through the 1930s.

Codes are usually minimum safety standards.

However, in the vernacular, "code" is a loose term that includes national, state, county and local laws and ordinances that dictate or direct building practices of all kinds. The whim of the inspectors could also loosely be considered "code". Most of the time, the basis of these laws and whims are guided by or reference/include the works of standards bodies, such as the National Electrical Code, NFPA, and International Plumbing Code, to name a few.

Depending on the jurisdiction and disposition of the building inspectors, a good way to make sure you will meet code for a particular project is to ask the inspector to look at your plans before you start your work. Your mileage here will vary greatly. Some jurisdictions won't even return your calls if you're not a contractor.

A good way to plan a project is to find a book at your local hardware store on the subject. While "code" varies from place to place, there is a lot of uniformity and common ground. These practices will generally be followed in these books. In fact, many times these books address code directly. A book I recently used on deck building referenced the International Residential Code specifically in many sections when explaining a decision to be made.