Copper metal is the best conductor among other metals due to its better conductivity and abrasion resistance. You can find copper wires in two types, solid and stranded. However, in many applications, electricians find the stranded wire more suitable. Why stranded wires have such extensive usage? Let’s dig in.
What is Stranded Wire?
Several thin threads of conductors twisted together and wrapped in insulation cover in stranded wires. You can find them in many sizes worldwide—for example, 7/32 in the US, 3/0.029″ in the UK, etc.
Stranded wires offer more flexibility than solid wires. Thus, electricians prefer it in electronic devices where you need to bend the wires through the corners, pass them through the walls or use them on points of repetitive motions.
Moreover, the stranded wires are also present in transmission and distribution lines because it reduces the “Skin Effect” in the overall transmission. (In the skin effect, the electrical current flows towards the outer surface of conducting wire instead of the whole area.)
However, some outdoor applications result in heavy corrosion and ampacity. A stranded wire may not be the best choice for such areas. Additionally, the stranded wires may become costly in some places.
Caption: Bare stranded copper wires
Conductor Strand Types
Several strand types offer unique characteristics to a stranded wire.
There are layers of strands around the core in a concentric strand wire as your layer has six wires more than in the layer before it. Other than in compact stranding, the directions of every layer are opposite to each other.
In Bunch stranding, there is no focus on geometric arrangement. Thus, you will observe the individual strands in the same direction.
Rope strands consist of concentric strands of the conductor, where every strand also has thin threads. Hence you can describe it by telling the number of each bundle that forms the rope and the number of strands in each bundle.
A sector conductor is a stranded conductor with a cross-section that’s like the shape of a segment of a circle, like a piece of a circle. If a cable has many sector conductors, it has a smaller surface area than the same cable that had round conductors.
In segmental conductors, three or four portions are insulated from each other. Such design gives the electrical wire advantage of less AC resistance as now the current has more area to flow and less skin effect.
It is a circular, multi-stranded conductor with a core with conductor strands around it. Non-conducting material is commonly used for most of the core, if not all. This design provides a lower total AC resistance for a given cross-sectional area of conducting material because of the skin effect.
Conductors with all layers wrapped in the same direction are called compact stranded conductors. There are no overlapping or air spaces in the finished conductor, and the surface is extremely smooth. As a result of this, the diameter is reduced.
Compressed wires range between standard concentric wires and compact conductors.
There is much room between the wires in a concentric wire because they are all in a round shape. When a conductor is compressed, the manufacturers pass it through a machine that reduces the distance between its wires. After performing each wire to form a trapezoidal shape, they strand the wires together to form the final conductor. It reduces the distance between wires even further. The diameter of a compact conductor is thus smaller than concentric one.
Caption: Steel rope stranded wire
The Stranded wire ampacity chart
As you want to look into the chart, you should learn some basics on ampacity.
The relationship between the AWG wire size and the ampacity
The AWG terms for the size and current capacity of a wire. For example, take a 10 AWG and a 20 AWG wire. You will see that the 10 AWG is greater in size than the 20 AWG wire. Thus, the greater the AWG of a cable is, the smaller the diameter across the area is. Remember, the gauge is inversely proportional to the diameter of the wire.
Moreover, in greater gauge wires, current capacity or ampacity is lower. It means that lesser current will pass in greater AWG wire. Hence, ampacity is also inversely proportional to the wire gauge.
Resistance is the force to oppose the current flow in a wire. In a standard cable, the greater is the gauge value, the higher the resistance to the current. Some experiments also suggest that the resistance doubles as you increase the gauge size by three. Moreover, as you increase the AWG by 10, the resistance increases up to ten times from the original.
Solid vs. Stranded wire: AWG sizes
It’s important to note that the AWG chart is for a single, round, solid conductor. Stranded wire is always larger than solid copper wires of the same AWG because of the gaps between the strands.
You can also describe the stranded wire using AWG gauges. A stranded wire’s AWG gauge is based on the total cross-sectional area of the strands, not the gaps in them. These gaps take up about 25 percent of the area, so the overall bundle diameter must be about 13 percent larger than a solid wire of the same gauge when using circular strands.
Moreover, you can describe the stranded wires with three measures, the overall AWG size, the number of strands, and the AWG of a single strand. Here, a slash separates the strand’s number and its AWG number. For example, a 22 7/30 AWG stranded cable is a 22 AWG cable with seven strands, each of 30 AWG.
Caption: Inside of a stranded wire
How to calculate the AWG of a stranded wire?
There is one method to calculate the AWG of a stranded wire. As a rule of thumb, you can translate the difference of AWG of two wires into a ratio of area or diameter. This rule applies when you need to find the AWG of a curtain wire with several strands.
Measuring strand diameter is more convenient and accurate than measuring bundle diameter and packing ratio in many cases. Hence, you can use wire gauge tools like the Starrett 281 or Mitutoyo 950–202. Also, you can use a caliper or micrometer to make such a measurement.
Stranded vs. solid wire: Who carries more current?
The gauge designation of solid and stranded wires is typically used to indicate the equivalent diameter of the wire. Generally speaking, a stranded wire of 14 gauge will be able to safely carry the same amount of current as a solid wire of the same gauge.
Interestingly, stranded wires have greater current carrying capacity than solid wires, which is surprising. Companies make stranded wires of 7, 19, or 31 strands with a much smaller diameter to make nice bundles (more is the number of strands, greater is the flexibility). If we stick to integer numbers of strands and use the standard sizes of thinner wires available, the output is never the same as the solids. As a result, you will select the strand wire gauge in such a way that the total cross-section remains the same or is slightly increased in size.
Caption: Different cable types
AWG wire sizes And the ampacity chart
All in all, the ampacity of the stranded wire is related to many factors, including the length and the cross-section of the cable. This table tells us the ampacity of different AWG at temperature rating per unit length. Also, the table uses copper wire with a plastic covering for the readings.
Stranded wires are made up of conductor strands twisted. These are flexible and ideal for applications where you have to turn the cable a lot. There are many types of conductor strands arrangements with specific usage. Thus you can choose the type which suits you best. Here at Bloom, we offer wiring harnesses and cable assemblies. Your connection is made with attention to detail. To avail of our services, contact us now.