About Wire

Stranded Wire and Solid Wire:

Stranded wire is helpful, especially in larger wire sizes to enable more flexibility in routing of the wire and offers more durability for applications where vibration and occasional movement of the wire could cause breakage of a stiffer solid wire.

Generally, for small wires sizes and for static applications with low levels of vibration, a solid wire is chosen as it is easy to bend and route, and low cost. An example of this is Romex type household wire common in #12 and #14 AWG sizes.  As wire and cables increase in gauge, only stranded formats offer practical levels of flexibility for routing.  As cables get larger still, there is increased need for finer stranding to allow adequate flexibility for ease of routing.

As an alternative to making large cable flexible the use of paralleling may be employed. In sizes of 1/0 and larger 2 or 3 or more cables may be used side by side provided that the same size, stranding and insulation ratings are used.

Terminal lugs for paralleling wire allow these multiple wires to be properly tied together at the both ends of the wire run.

Industrial stranded cable is a coarse stranding class and known as “semi-rigid” stranding types. The idea is that the stranding allows enough flexibility to bend wire without needing to go to full “flex” wire stranding such as those used for mobile power applications like locomotive cable, welding cable and machine tool traveling power cables.

Areas of solid and stranded the same:
The total cross-section area, AWG or "circular mill" size of a stranded conductor is equivalent to that of a solid conductor for the same designated wire size. This means when looking at a "Number 10 solid wire," compared to a "Number 10 stranded wire" the latter will look slightly larger in diameter but has the exact same total cross-section area of conductive material as the solid Wire. This means the current carrying capacity is the same too.
Similarly, there will be no less or more voltage drop whether you use stranded or solid wire and the current carrying capacity is the same. The main reason for using stranded is for ease of installation and routing, as it is easier to work with in the larger sizes, because it is more pliable. Also solid wire is not so resistant to vibration and repetitive movement compared to stranded wire so solid wires are for totally static applications.  

Stranded wire is a larger diameter:
Stranded wire has a bigger overall diameter than solid wire due to the air trapped between strands and a correspondingly larger insulation diameter needed to cover the wire.
To overcome the need for more routing space for flexible wire, some stranded wire types are “compressed” or “compacted” before applying the insulation layer. These wires are cold formed to reduce the diameter of the strands of wire, squeezing out the air spaces while maintaining separation of the strands, which allows much of the flexibility to remain.

Advantages of Solid Wire:
   1. More compact for the same current capacity.
   2. Lower cost (market forces may apply)

Disadvantages of Solid Wire:
   1. Only practical and available in small sizes.
   2. Flexing or vibration will fatigue the wire and cause it to break.

Advantages of Stranded Wire:
1. More flexible for routing
2. More durable for vibration and infrequent movement.

 Disavantages of Stranded Wire:
   1. Larger size.    
   2. More costly especially as stranding increases as more processing is required to manufacture it.