Building Wire – NM Cabling
Steve Maurer, IME
If you're an electrician, you're probably familiar with the various types of building wire, from residential to commercial to industrial. You're likely cognizant of the NEC® regulations for each area. It's not unusual for some head scratching and confusion on some of them. So my best advice when in doubt, contact your local or state inspections office for clarification.
That said, let's look at some of the types of building wire available today.
Residential building conductors and cabling
Probably the most common types of indoor wiring in residential applications is NM, NM-B and NMC). Its construction consists of two or more copper conductors and a covered or bare copper conductor, all encased in a PVC or other nonmetallic jacket.
Back in the day (say, before 2001), most NM cable had a white jacket. Since that date, manufacturers adhere (for the most part) to a recommended color code. This makes it easier for installers and inspectors to identify conductor size (and type) at a glance. The colors are:
Another designation pertains to number of conductors. I don't think you'll find any cable with only two conductors. But you will find, for example, 12-2 with ground for two 12 AWG conductors, black for hot and white for neutral, and one ground conductor, either bare copper or with a green jacket. A 12-3 with ground will have an additional conductor, coded red for an additional hot.
Some manufacturers offer an "X" AWG-4 with ground that will give you two hot and two neutral conductors, along with a dedicated ground.
Many NM cable manufacturers have formulated an outer jacket with a special coating to make pulling the wire easier and simpler.
About 15 years ago, I got the itch to rewire our entire house. Honestly, the previous wiring job was, well, hideous. Seems they used whatever they had laying around, including UF, in the attic. If they ran out of cable before the end of the run, they just put in a box, made a splice, and continued onward.
Not cool.
So I rewired the entire mess, using white for the lighting, yellow for the receptacles, orange for some appliances, and so forth. It took me all of a long, hot summer.
At this time, I do want to clear something up.
I know what you're thinking. "Steve, you're talking about Romex cable, right?"
Well, yes … and no.
First, the no.
Calling all NM-B cable Romex® is like calling all tissue paper Kleenex®. Romex® brand NM-B cable is owned and manufactured by Southwire®. Their specially formulated coating for making pulling the cable simpler is SIMpull®.
Romex® has just made it's way into the collective consciousness of electricians everywhere. But there are other brands of NM cable.
But yes, I did use Romex® Brand SIMpull® NM-B cable to rewire my entire house.
It said so right on the protective jacket.
However, I recently came across another innovation that also excites me.
Power and control in one cable
If you've been reading my stuff, you already know I'm an LED nut. And dimming lights is the name of the game. Many LED fixtures include a separate set of wires for ON/OFF and dimming chores. It's low voltage, 0-10 volts, and that means running a separate cable of conductors just for those tasks.
But at least one manufacturer—Southwire®—has included the signal/control cabling right alongside the NM cable. It's in a separate, yet attached jacket, marked with a stripe. The solid copper 16 AWG conductors are jacketed with purple and pink insulation and are rated for Class 2 or Class 3 circuits.
Note: these separate conductors are not for 120 volt AC line connections. They're strictly for low voltage applications. By the way, these power/control cables can be purchase separately from the 120-volt cables.
Something to think about during a retrofit.
If you're running cable from the switch or dimmer to a fixture equipped with low voltage control, you really need to check this out.
Remember to follow all electrical code requirements for NM cable installations. Make sure to use the correct cable for each application.
That said, let's look at some of the types of building wire available today.
Residential building conductors and cabling
Probably the most common types of indoor wiring in residential applications is NM, NM-B and NMC). Its construction consists of two or more copper conductors and a covered or bare copper conductor, all encased in a PVC or other nonmetallic jacket.
Back in the day (say, before 2001), most NM cable had a white jacket. Since that date, manufacturers adhere (for the most part) to a recommended color code. This makes it easier for installers and inspectors to identify conductor size (and type) at a glance. The colors are:
- White – 14 AWG conductors for 15-amp use
- Yellow – 12 AWG for 20-amp use
- Orange – 10 AWG for 30 amp use
- Black – both 8 and 6 AWG for 40-amp and 55-amp respectively (check the label)
- Gray – for underground feeder applications (read the label for conductor size)
Another designation pertains to number of conductors. I don't think you'll find any cable with only two conductors. But you will find, for example, 12-2 with ground for two 12 AWG conductors, black for hot and white for neutral, and one ground conductor, either bare copper or with a green jacket. A 12-3 with ground will have an additional conductor, coded red for an additional hot.
Some manufacturers offer an "X" AWG-4 with ground that will give you two hot and two neutral conductors, along with a dedicated ground.
Many NM cable manufacturers have formulated an outer jacket with a special coating to make pulling the wire easier and simpler.
About 15 years ago, I got the itch to rewire our entire house. Honestly, the previous wiring job was, well, hideous. Seems they used whatever they had laying around, including UF, in the attic. If they ran out of cable before the end of the run, they just put in a box, made a splice, and continued onward.
Not cool.
So I rewired the entire mess, using white for the lighting, yellow for the receptacles, orange for some appliances, and so forth. It took me all of a long, hot summer.
At this time, I do want to clear something up.
I know what you're thinking. "Steve, you're talking about Romex cable, right?"
Well, yes … and no.
First, the no.
Calling all NM-B cable Romex® is like calling all tissue paper Kleenex®. Romex® brand NM-B cable is owned and manufactured by Southwire®. Their specially formulated coating for making pulling the cable simpler is SIMpull®.
Romex® has just made it's way into the collective consciousness of electricians everywhere. But there are other brands of NM cable.
But yes, I did use Romex® Brand SIMpull® NM-B cable to rewire my entire house.
It said so right on the protective jacket.
However, I recently came across another innovation that also excites me.
Power and control in one cable
If you've been reading my stuff, you already know I'm an LED nut. And dimming lights is the name of the game. Many LED fixtures include a separate set of wires for ON/OFF and dimming chores. It's low voltage, 0-10 volts, and that means running a separate cable of conductors just for those tasks.
But at least one manufacturer—Southwire®—has included the signal/control cabling right alongside the NM cable. It's in a separate, yet attached jacket, marked with a stripe. The solid copper 16 AWG conductors are jacketed with purple and pink insulation and are rated for Class 2 or Class 3 circuits.
Note: these separate conductors are not for 120 volt AC line connections. They're strictly for low voltage applications. By the way, these power/control cables can be purchase separately from the 120-volt cables.
Something to think about during a retrofit.
If you're running cable from the switch or dimmer to a fixture equipped with low voltage control, you really need to check this out.
Remember to follow all electrical code requirements for NM cable installations. Make sure to use the correct cable for each application.
Photo courtesy of Southwire
