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I replaced a fixture today that had a piece of 12Ga stranded (probably THHN) wire used as a pigtail. The building has some wiring in conduit (other wires in this box were solid), so I'm guessing that's what the prior person had handy.

If this is a legitimate use, it seems that it may be worth keeping a bit of stranded wire handy, as the pigtails would be a little easier to work with in a tight box.

I'm in CT, USA.

  • As long as the connector used is listed for both solid and stranded and is properly sized, and the terminal the pigtail is terminated on is listed for stranded wire. – Tester101 Mar 20 '15 at 2:44
  • What type of connector are you using to connect the stranded wire to the solid wire? What is the stranded wire terminating on? – Tester101 Mar 20 '15 at 2:47
  • It was connected to two strands of solid with a wire nut, and terminated on a screw terminal of a light switch. – TomG Mar 20 '15 at 3:03
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As long as all the equipment is listed for the use, there's no problem using stranded wire. The UL White Book says that screw terminals and pressure plate terminals can be used with both solid and stranded wire.

UL White Book 2013

Receptacles(RTDV)

Receptacles for Plugs and Attachment Plugs (RTRT)

Terminals
Terminals of the wire-binding screw, setscrew, or screw-actuated backwired clamping types are suitable for use with both solid and stranded building wires.

It says switches are solid only, however, you can use terminal connectors such as fork connectors.

Switches (WFXV)

Snap Switches (WJQR)

Terminals
Terminals of the wire-binding screw, setscrew, or screw-actuated backwired clamping types are suitable for use with solid building wires unless otherwise indicated either on the device or in the installation instructions.

Terminals of a flush snap switch are permitted for use with Listed field-installed crimped-on wire connectors or an assembly, if so identified by the manufacturer.

A flush snap switch may also be provided with conductor leads with factory-installed crimped-on connectors. Such connectors may be either attached to the flush snap switch terminal or are provided with the flush snap switch in the smallest unit shipping container and are suitable for use with the terminal of the flush snap switch.

Wire connectors (including twist-on wire connectors) can be used for both solid and stranded wire sizes between 30-10 AWG, in combinations listed by the manufacturer. Unless they are clearly marked to be used with one type or the other.

Wire Connectors (ZMKQ)

Wire Connectors and Soldering Lugs (ZMVV)

Wire stranding -- Unless clearly marked "Solid," "SOL," "Stranded" or "STR" for a given wire size, wire range or wire combination, conductors in the range 30-10 AWG are both solid and stranded, and 8 AWG and larger are for stranded wire only.

Ideal Industries has a handy PDF, that lists all the allowable wire combinations that can be used with their various connectors. For example, the Ideal 74B® (their basic yellow wire-nut) can be used with 1 - 4 #14 solid or stranded conductors.

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  • As this question suggests, using fork connectors can make terminating the wire at devices easier. – Tester101 Mar 20 '15 at 3:46
  • Is the "switches" quote accurate? It doesn't state "solid and stranded" like the receptacles quote. – TomG Mar 20 '15 at 11:42
  • @TomG You're correct, I missed that (sorry I was tired). I've updated my answer. – Tester101 Mar 20 '15 at 12:41
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Yes, stranded wire is okay; see Tester101's answer for more details.

However, I'd like to add some advice: from experience, solid-wire is both easier and more reliable to pigtail, so if you have a choice, prefer the solid wire.

Also, after seeing multiple correctly-sized and -screwed wirenuts gradually slide off of stranded wire, I now always wrap the wire + wirenut in a bit of electrical tape when working with stranded wire. Some electricians always do this, but I've never had any issues when only working with solid wire (Disclaimer: I am not a professional electrician).

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