Although knob-and-tube wiring prevailed for years, other types of wiring were developed in attempts to either speed up or simplify installations. If your house was built prior to the 1950s, you might find one of these not-so-fun types of wire in it. Unfortunately, every innovation doesn’t stand the test of time.
The following two systems were later contemporaries of knob-and-tube wiring:
➤ Armor-clad cable
➤ Multiconductor cable
Armor-clad cable, often called BX, was a trademark of General Electric. It consisted of a narrow metal sheathing wrapped around the hot and neutral conductors. It was mainly installed in the 1920s and 1930s in more expensive housing. Running the wire in a protective metal wrapping sounds like a good idea, right? It probably was until the metal started rusting and corroding with age. Then the hot wire could short out to the metal wrapping, and in some cases, the wrapping could become red-hot but never blow a fuse. This type of wiring should always be thoroughly inspected by an experienced electrician.
Multiconductor cable carried both the hot and neutral wires in a cloth insulation that was coated with either varnish or shellac. Each wire was separately wrapped in its own insulation as well. As it ages, the insulation becomes very brittle and is almost impossible to work with in some cases.
Current systems use nonmetallic sheathed cable commonly known as Romex, another trade name. This cable is wrapped in thermoplastic, which probably will last so long that future anthropologists will be carbon-dating it in the year 14,500 C.E. This is a very safe wiring system that comes with a grounding wire in addition to the hot and neutral wires, and it allows for relatively quick and efficient installation.
The following two systems were later contemporaries of knob-and-tube wiring:
➤ Armor-clad cable
➤ Multiconductor cable
Armor-clad cable, often called BX, was a trademark of General Electric. It consisted of a narrow metal sheathing wrapped around the hot and neutral conductors. It was mainly installed in the 1920s and 1930s in more expensive housing. Running the wire in a protective metal wrapping sounds like a good idea, right? It probably was until the metal started rusting and corroding with age. Then the hot wire could short out to the metal wrapping, and in some cases, the wrapping could become red-hot but never blow a fuse. This type of wiring should always be thoroughly inspected by an experienced electrician.
Multiconductor cable carried both the hot and neutral wires in a cloth insulation that was coated with either varnish or shellac. Each wire was separately wrapped in its own insulation as well. As it ages, the insulation becomes very brittle and is almost impossible to work with in some cases.
Current systems use nonmetallic sheathed cable commonly known as Romex, another trade name. This cable is wrapped in thermoplastic, which probably will last so long that future anthropologists will be carbon-dating it in the year 14,500 C.E. This is a very safe wiring system that comes with a grounding wire in addition to the hot and neutral wires, and it allows for relatively quick and efficient installation.
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