Inspection Training

How to Inspect the Electrical Branch Circuitry

While the inspector is at the electrical panel and in the attic they should be checking for any signs of knob and tube wiring. If the inspector comes across knob and tube they should use the non-contact voltage tester to check if the wiring is active. Regardless of whether or not it is active, the inspector should call the presence of this wiring out in the report as a defect. Please review the entire procedure below.


International Standards of Practice for Performing a General Home Inspection


3.7. Electrical


I. The inspector shall inspect:



II. The inspector shall describe:



III. The inspector shall report as in need of correction:



IV. The inspector is not required to:



Axium SOP Differences

Axium Requires: The inspector should view the electrical branch circuitry


Tools Needed

The inspector would need to use the non-contact voltage tester if there is knob and tube wiring that is present.



  • While the electrical panel front cover is off the inspector should view all of the wiring in the panel for any damage or splices. They should also make sure to point out if the wiring is knob and tube. There is not a picture required for this section if there are no defects.


Common Defects

  • Any wiring that is damaged or spliced incorrectly.
  • Knob and Tube wiring that is present in the electrical panel or in the attic.

Common Mistakes

  • Not closely examining the wiring in the electrical panel or in the attic.
  • Not determining if the wiring is knob and tube.

Report / Software 


  • Accessible branch circuit conductors were examined and were in acceptable condition and amperage and voltage were compatible.


  • N/A


  • N/A


  • Knob Tube: The property has knob-and-tube wiring. Knob and tube wiring (sometimes abbreviated K&T) was an early standardized method of electrical wiring in buildings, in common use in North America from about 1880 to the 1930s. It consisted of single-insulated copper conductors run within wall or ceiling cavities, passing through joist and stud drill-holes via protective porcelain insulating tubes, and supported along their length on nailed-down porcelain knob insulators. Where conductors entered a wiring device such as a lamp or switch, or were pulled into a wall, they were protected by flexible cloth insulating sleeving called loom. The first insulation was asphalt-saturated cotton cloth, then rubber became common. Wire splices in such installations were twisted together for good mechanical strength, then soldered and wrapped with rubber insulating tape and friction tape (asphalt saturated cloth), or made inside metal junction boxes. Historically, wiring installation requirements were less demanding in the age of knob-and-tube wiring than today. Compared to modern electrical wiring standards, these are the main technical shortcomings of knob-and-tube wiring methods: never included a safety grounding conductor did not confine switching to the hot conductor (the so-called Carter system places loads across the common terminals of a three-way switch pair) permitted the use of in-line splices in walls without a junction box (and thus exposing a potential fire hazard of an uncontained spark caused by arcing following mechanical failure of the splice). Most existing residential knob and tube installations, dating to before 1940, have fewer branch circuits than is desired today. While these installations were adequate for the electrical loads at the time of installation, modern households use a range and intensity of electrical equipment unforeseen at the time. Household power use increased dramatically following World War II due to wide availability of electrical appliances. Modern property buyers often find that existing K&T systems lack the capacity for today’s levels of power use. First-generation wiring systems became susceptible to abuse by property owners who would replace blown fuses with fuses rated for higher current. This overfusing of the circuits subjects wiring to higher levels of current and risks heat damage. Knob-and-tube wiring may also be damaged by building renovations. Its cloth and rubber insulation can dry out and turn brittle. It may also be damaged by rodents and careless activities such as hanging objects from wiring running in accessible areas like basements. For those concerned about stray magnetic fields, knob- and-tube wiring produces a much stronger effect at a given level of current, since the conductors are separated by a greater distance and their fields do not cancel as well as more closely-spaced conductors. Currently, the United States NEC forbids the use of loose, blown-in, or expanding foam insulation over K&T wiring. This is because K&T is designed to let heat dissipate to the surrounding air. As a result, energy efficiency upgrades that involve insulating previously uninsulated walls usually also require replacement of the wiring in affected properties.