When purchasing older real estate to live in, rent or flip in Phillipsburg, New Jersey, Belvidere, New Jersey or Washington, New Jersey; one of the many things that will need attention is the building's wiring. Old buildings often contain legacy wiring types, such as the infamous "Knob and Tube" wiring method. This method, often noted on home inspection reports is a 2-wire system featuring a "hot" conductor and a neutral conductor. Each circuit is run through sets of porcelain tubes drilled through joists and studs, or secured to knobs when running parallel with framing members. This wiring method was in common use from the 1880's to 1940's.
While Knob & Tube is easily the most infamous, there are other wiring methods that should give home buyers pause. Among these are Cloth insulated BX. BX wire looks similar on the outside to today's Armored Cable or Metal Clad cable used in commercial and industrial settings throughout the country. It features a corrugated steel jacket with a "hot" and a neutral twisted together inside. Often there is a paper liner between the steel and cloth. It features a similar pre-plastic cloth insulation on the conductors. This type of wiring was used beginning in 1910's, becoming common in the 1920's and widespread through the 50's
In addition to the aforementioned wiring systems, we also come across Non-Metallic cloth-insulated cable- "NMC." This wiring looks similar to modern day NM cable commonly referred to as "Romex." However rather than the color-coded PVC outer sheathing, this wire type features a braided or woven cloth insulation and/or sheathing. Some of these cables have the braided cloth sheath on the outside but feature modern appearing rubber (not plastic) insulation on the conductors. The rubber has dried out and become brittle over time as well. Other earlier NMC cables will contain cloth insulated wires inside the outer jacket, leading to the same unsafe condition in Knob & Tube and Cloth BX cables. This type will often lack an equipment grounding conductor. In use from the 1950s-1960s.
Knob & Tube-The method didn't always rely on cloth to insulate the hot from the neutral, it relied on physical isolation and porcelain insulators keep them apart when run in attics and basements. However, it was common when entering wall cavities to "loom" the wires together to enter a box. This means the wires are touching and relying on deteriorated, tar-soaked cloth for insulation. The original soldered and friction tape joints are strong and reliable, if undisturbed. The biggest issues are where modifications and splices have been made later. When ran exposed in basements and attics, it presents an electric shock hazard, because there are spots where the wire is bare.
Cloth Insulated BX-Less likely to be damaged by rodents and mechanical damage, no exposed copper on insulators. The metal outer jacket can act as an equipment ground when installed in metal outlet boxes with proper clamps. If a grounding-type receptacle is used with an equipment grounding jumper from the outlet to the box, the outlet will often read "grounded." However, the deteriorated cloth insulation will often leave wire exposed right at the point where the outer jacket is stripped off, meaning high risk of arcing (fire risk) and (hopefully) breakers tripping.
Cloth Insulated NMC-The worst of both worlds. Cloth covering on conductors has deteriorated, especially where it enters boxes. But unlike BX, the non-metallic sheath can't act as an equipment ground, so these circuits will always produce "open ground" receptacles. The cloth sheath isn't as strong as the BX sheath, leaving it susceptible to mechanical and rodent damage. Since there is no metal sheath on the outside to ground, damage to the insulation may not result in a ground fault, meaning the breaker may not trip.
The best course of action is to replace these wiring types entirely. Many of these installations are over 100 years old. All too often we see updated finishes such as new floors, cabinets and appliances, but no updates have been made to the home's wiring. Installing new wiring provides a safe foundation for any renovation project.
At minimum:
Make sure your electrical panel is a modern circuit breaker design, such as Square D, Eaton and Siemens and not Edison Fuses, Federal Pacific, Wadsworth, Zinsco or Pushmatic
Install modern dual function Arc Fault/Ground Fault breakers
Update your home's grounding electrode system and water pipe bonding so if there is a wire touching a pipe, the overcurrent protection can operate
Beware that even minor tasks such as replacing light fixtures and receptacles present a hazard if not handled properly.
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