Is Old Wiring Safe?
Old Wiring: Is It Safe?
Today's standard household wiring is a plastic-sheathed, insulated
three-wire cable, universally known by the trade name Romex. But the vintage copper wiring in many older houses
works just as well as the new stuff, as long as it's in good condition and hasn't been altered in a way that
violates code. Here are some wiring systems you'll find in older homes.
Knob and Tube
The earliest residential wiring system has a cloth-covered hot wire and a neutral
wire, which run parallel about a foot apart. Ceramic knobs anchor the wires to the house framing; ceramic tubes are
used where wires cross or penetrate framing.
Caveats: Cannot be
grounded or spliced into a grounded circuit. Its soldered connections may melt if too much current flows through
them. Rewire or disconnect any circuits covered with building insulation; it causes this wiring to
overheat.
Armored Cable (Bx)
The successor to knob and tube. A flexible steel sheath covers hot and neutral wires,
which are insulated with cloth-covered rubber. The sheath provides a ground, so grounded receptacles are easy to
retrofit.
Caveats: Sheath must be
anchored securely to a metal outlet box. Check condition of insulation every five years or so; it degrades over
time, as shown above, or if too much current is allowed to flow through the circuit.
Two-wire plastic-sheathed cable
An early PVC-insulated (Romex) wire.
Caveats: Plastic is easily
damaged. Grounded receptacles cannot be retrofitted to this wire.
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