Not all copper wire is created equal, but knowing when to use which type of wire and where can potentially save you a ton of time, money, and headaches.

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For the same reason you wouldn’t use a Honda Fit to tow a camper, you likely wouldn’t use THHN wire in a direct burial situation – it simply isn’t a good wire for the job. The same can be said for deciding when to use a solid copper wire versus a stranded version.

At first glance, it might seem like every type of copper cabling does the same job. However, the distinction between stranded and solid wire becomes more important when considering the application.

How Is Solid Copper Wire Made?

To make solid copper wire, rods are drawn down using a series of smaller and smaller dies to reach the gauge needed for the application it’s being used for.

As the copper is stretched out, it gets thinner and more brittle. To fix the brittleness and prepare the cable for use, it goes through a process called annealing. During annealing, the wire is heated, making it stronger and more ductile.

After the wire is annealed, it’s ready for use as a bare copper product or can be insulated and used as a telecom, pet fence, or tracer wire.

How Is Stranded Copper Wire Made?

Stranded or bunched cable is multiple individual strands of smaller gauge wire twisted together to create a larger gauge product.

To make stranded copper, individual wires are drawn and annealed. Once they’re ready, they’re then run through another machine that twists them around a center wire.

Depending on the gauge needed, these strands can be composed of seven or more 30 or 34 AWG (American Wire Gauge) strands. As more strands are added, the resulting wire gains more flexibility.

It also matters how the wires are twisted. For example:

• Class B wires, which include standard power cables, XHHW, and USE/USE, are twisted concentrically. As more layers are added, the direction is reversed.
• Class K, associated with SIS (aka switchboard or panelboard) cable, can be bunched or rope-laid. Bunched wires don’t have a specific pattern associated with them. Rope-laid cables feature several bunches of wire twisted together.
• Class M cabling is used in situations where flexibility is key. It is comprised of smaller gauge wires.

Stranded Wire vs. Solid Wire: Which One Is Better?

To answer this question, the first thing that needs to be done is to assess the situation.

Is the project going to be one where flexibility is crucial? Is there a threat of corrosion? How long is the run? All of these play a critical role in determining which cable is needed.

Strength

Solid copper is stronger than stranded copper. This is because the conductor is thicker and is one solid piece of metal, as opposed to a bunch of smaller cables twisted together.

Cost

Solid copper is cheaper for manufacturers to produce because the process is faster and includes fewer steps – it only needs to be drawn, annealed, and insulated (if necessary).

Stranded copper follows the same process, but the wires have to be twisted together to form the finished product. This adds more time and costs to the manufacturing process.

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Flexibility

Solid wire is strong and rigid. Those qualities are great for applications that require strength, but not so much for pliability. Stranded wire is much more flexible, making it easier to route and work within tight spaces.

Load Capacity

Despite the final gauge being the same, a solid wire will have less surface area than a stranded or bundled one, giving it a higher load capacity and less impedance. Solid wire also has a lower voltage drop over long runs but heats up faster than stranded cable.

Stranded has a higher surface area because it’s made up of several different wires rather than only one conductor. There is a larger voltage drop over long runs, but stranded wire doesn’t heat up as quickly because of air gaps that form as the wire is twisted together, allowing heat to dissipate along the length of it.

Corrosion

A single, solid wire will withstand corrosion better than a stranded one because there are fewer spots for corrosion to occur.

Remember those air gaps mentioned a few sections ago? Those same air gaps that make for a flexible, easy to bend wire also provide many more opportunities for corrosion to eat away at the individual strands. Conductors can also be tinned to impede corrosion.

Applications

Solid cable is strong, making it an excellent fit for situations where ruggedness is key. It works well in outdoor situations with approved sunlight-resistant insulation and is good for direct burial applications, including as a tracer wire.

Stranded copper is easier for installers to handle in tight areas and inside buildings because it is more flexible and faster to manually manipulate.

Stranded vs. Solid Wire? There’s No Competition

Cutting corners or using the wrong wire may be cheaper or faster at first, but those early mistakes have the potential to become major problems as the years wear on.

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There are many differences between stranded wire and solid wire, the two most popular types of wiring.

In this post, we will discuss their pros and cons, and when to use stranded wire vs solid wire, to help you decide which type is best for your needs.

Thermocouple and resistance wires can all be manufactured as solid or stranded wires.  In the case of stranded resistance wires, the individual strands are carefully manufactured by stranded wire suppliers to ensure the finished resistance is within the specification.

Without further ado, let’s dive into the difference between solid and stranded wire!

Stranded Wire vs Solid Wire

By Stephen Holt, Technical Manager since

Advantages of Stranded Wire:

Before we discuss its advantages, we should point out that there are many different types of ‘stranded wire’, from plain, bunched wire to super-flexible, multilayer, concentric rope strands.  

• The main advantage of stranded wire is that it is much more flexible than solid wire.  Twisting together a number of finer wires reduces the strain on each one when the conductor is flexed making it less likely for the wire to break.
• The spiralling also increases the conductor’s ability to withstand thermal expansion and contraction strains.

Disadvantages of Stranded Wire:

• More expensive: Stranded wire costs more than solid wire because it is more complex to manufacture.  You have to make multiple, smaller wires, which are then twisted together, sometimes passing through the laying up machines several times (in the case of rope stranding for instance) to create the finished product.
• Stranded wires can be more difficult to terminate.  When removing the insulation, you have to be careful not to break off the ends of any of the individual wires and ensure they are all fitted into the terminal.  You can use a ferrule to hold the wires together, but need to be careful if the conductor is a thermocouple wire. The ferrule would need to be made from the thermocouple material in order not to introduce another thermocouple junction into the system!
• Compared to solid wire, stranded wires have a greater diameter.  The solid or stranded conductors are specified to maintain the cross-sectional area of metal so that the resistance is the same and they carry the same current, but a stranded wire cross-section will include air gaps between the wires, increasing the overall size.
• Finish: a stranded wire will not be as smooth as a solid wire.  This does not matter if you are covering it in a thick wall insulation like PVC, but some fluoropolymer insulations are only 0.3mm thick and need to go over a smooth surface for them not to crack.  Stranded conductors for thin wall insulations have to be made up of thin individual wires, laid up concentrically to provide a smooth surface.

Advantages of Solid Wire:

• Solid wire is easier to terminate as the insulation can be removed without risk of breaking the fine wires in a stranded construction. It is also significantly cheaper.
• Solid wires are often easier to fit in electrical panels.  Although they are stiffer to bend, once they are, they stay in place and can be slotted into the terminal blocks in neat rows.

Disadvantages of Solid Wire:

• Poor flexibility: While solid wire is less expensive to manufacture than stranded wire, it cannot be used in environments where the cable has to be flexed.  The conductor and insulation will break if they are repeatedly moved.  Consequently, solid wires are only suitable for fixed installation situations.

Stranded Wire vs Solid Wire: Which Should You Choose?

If you need help determining the right wire construction for your application, contact us and our technical experts can help you decide which is the most appropriate for your project.

For more information, please visit Stranded Steel Wire.