- 1). Look for labeling on the plastic sheathing that says "Romex." It can usually be found on newer Romex wire from the 1970s and later. There is also a number designation printed on the plastic sheath, either "12-2 G" or "12-3 G." The number 12 indicates the gauge, or thickness, of the wire, while the second number followed by the G specifies two or three live electric wires plus a ground wire.
Alternatively, the sheath may say "NM," which means non-metallic, and also give the maximum number of volts the wire can carry. It is also possible to find 13- and 14-gauge Romex wire along with the "2 G" and "3 G" designations (Reference 2). - 2). Rip approximately two inches of the plastic sheathing back using a Romex sheath ripper, a type of wire stripper made especially for Romex cable. Strip an unused portion of cable only after the main circuit breaker has been shut off at the main panel, and find an unused wire lead that has be closed off with a wire nut, a type of splicing device that twists onto the end of copper wire. Look for a bundle of three or four wires. A Romex bundle containing three wires will have a bare copper wire along with a black wire and a white wire. A Romex bundle of four wires will have one bare copper wire along with a white, red and black wire (Reference 2).
- 3). Verify the Romex cabling connects to secured junction boxes and electrical outlet boxes, as specified by the NEC, the National Electrical Code (Reference 3). These types of electrical outlet boxes are metallic or plastic and can be screwed or nailed directly to a stud or joist before the drywall is hung.
Look for a distinct looking metal box with the front face open, while each side has pre-cut circular holes that can be punched out to let the wiring pass through. The plastic box has little tunnels where nails can be driven through, and channels for the Romex wire to enter (Reference 2). You know you are dealing with old Romex when the cabling passes through housing studs one foot above the floor and is used to wire electrical outlet boxes. - 4). Look for pig-tailing, a Romex wiring technique using a wire nut that joins a single wire from the electrical outlet to two live Romex power wires. This is a way of consolidating the wiring. Look for this Romex wiring configuration in lighting fixtures, too (Reference 2).
- 5). Look for ceramic knobs and tubes running along the framing of the home. Finding this distinct electrical wiring type in a residential building rules out the presence of old Romex. Knob and tube wiring is an obsolete wiring convention that predates World War II and is usually found only in very old homes. The wires must be exposed to the air to dissipate heat and is vulnerable to damage (Reference 3).
Old Romex and knob and tube wiring is incompatible, so finding the presence of one rules out the presence of the other.
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