Which Wire To Use For My Project?

The choice of which wire and non-terminated cable to use depends solely on your application.  For various categories, the types of wiring to consider are listed.

Breadboarding and Prototyping

Many designs are tested using a prototype, a functional mockup of the circuit.  For electrical circuits, one of the most popular ways to prototype is to use a breadboard.  The breadboard has electrical connections allowing wires to be easily placed and moved as needed.

Breadboard wires are pre-cut flexible stranded wires of different lengths come with stiff tips.  These allow for very fast wire routing.  

Solid-core breadboad wire is usually 22 gauge and is stiffer than the pre-fab wires. Breadboard wire also comes in a number of colors.  These wires are cut by the user and about 3/8 inch (4 mm) of insulation taken off using a tool like a wire stripper. If you use a smaller wire gauge and force it into the breadboard holes, you can damage the breadboard.

Wearables

Conductive Thread: Adafruit caries different weights of stainless steel thread which can be washed and last longer than older silver based thread.  Two-Ply is the lightest thread while three-ply is a bit tougher and can handle more current. A final thread falls somewhere between a thick thread and a thin yarn. Most sewing machines wouldn't be happy with such thread since its thick, but it has the 'furry' soft feel of yarn, which makes it poor for most e-textiles/wearables but its high conductivity and softness make it a great thread for making smartphone gloves! 

Silicone-covered Stranded Wire: This wire bends well and the jacket covering is more flexible than morerigid PVC.  The 26 gauge wire is good for low power transfer while the 30 gauge wire is a bit thinner and good for signals or lower power transfer.

Ribbons: Ribbons with conductive wires embedded or with conductive thread (in black or white) have the wires already built-in for stealth.

Final Projects

For non-wearables, you can encounter many different environments for your project.  Here are a few examples of environments and materials you may use to built lasting projects.

Exterior Cabling requires taking into account changing temperatures and rough weather.  Outside cabling should have a jacket that can withstand the weather it will be exposed to.  Cable manufacturers provide temperature ratings for their cable (one hopes).  If you need additional protection, cables may be run in PVC pipe, EMT conduit or rigid pipe (for buried cables).  Local regulations may govern what type of conduit is acceptable.

Outdoor Enclosures protect your project from damage and dust while often providing the exterior finish to the electronics inside.  For outside projects, weatherproof enclosures are ideal.  Plastic and metal boxes come in many shapes.  But how can wiring enter an enclosure and maintain a weather-tight seal?  Cable Glands come in various sizes and allow cables to enter an enclosure with a tight seal.

Projects on the Move provide a particular challenge for wiring. This is true for robotics, automotive projects, and wearables.  The vibrations while moving may loosen connections.  Rather than use a breadboard as a permanent platform, soldered wire connections are often best. Adafruit's breakout boards have presoldered components able to withstand normal vibrations in mounted projects. If any wiring will flex, select the wire to withstand repeated bending but be aware that any wire will break with severe stress or very frequent flexing.

Rotating Parts provide a tricky challenge for wiring.  How does one connect electronics to something rotating like a robot's wheel or neck?  Adafruit's slip rings feed several wires through a rotating center providing the ideal coupling with no tension on the wires on either side.

Secure it - clips and bolts provide the mechanical connections in final projects. Most Adafruit circuit boards have mounting holes which accomodate mechanical screws to hold the board.  Standoffs are handy for spacing two circuit boards together.  For wiring, you can look for plastic cable clips and tie wraps to secure wiring to other rigid structures.  For tacking wires to a surface, a bit of hot glue or Sugru works very well.