All of us DIYers are familiar with a few different types of wire — at least in the guitar and amp world.  They are all rather similar, but seem to be used in different and very specific applications. In many cases, we tend to just accept that this piece of wire is used over here and this other piece of wire is only used over here, but it’s actually quite practical and pretty important to understand why these conventions exist and how they benefit the end user and the overall sound of gear.  Now this, like anything else in the guitar and amp universe, is a subject that can go down some deep dark rabbit holes if you let it go that far; many folks will resort to looking at graphs and data tables for pinpointed physical evidence to either prove or disprove these conjectures, because the fact is, there is a mathematical way to determine the appropriate wire to use for any given application.  Today, however, we are simply presenting some basic facts without going too far into the math, which should in turn give you a firm understanding of the differences between solid core and stranded wire, as well as large and small gauges of wire. 

Stranded Vs. Solid Wire
If you’ve ever popped open an old Fender amp, or if you’ve ever built an amp from a kit, you’ve likely seen the classic cloth-covered pushback solid core wire used almost as a standard in amplifier circuitry.  Conversely, if you open up your guitar’s control cavity you’ll be more apt to see stranded (and PVC-coated) wires implemented therein. And while many audiophiles claim they can hear the difference between stranded and solid wires, this typically has no bearing on how and why the different wire types are employed in the first place.  There is even the idea that AC current (like that produced by your guitar’s pickups) travels more efficiently along stranded wires because AC current only travels along the outside of any given wire anyway...but that’s still not the reason we use stranded and solid wires in different applications.  
The actual reason, which isn’t all that exciting or technical, is mere practicality.  If you’ve ever worked with a piece of stranded wire, you know that it is inherently flexible, where solid core wire is rigid, and tends to hold whatever shape it’s bent into.  Bend a piece of solid core wire back and forth a few times and it’s likely to snap into two pieces; this is where the use of stranded wire in certain applications really becomes practical.  
When you take your amp to a gig, you carefully pick it up and do your best not to go smacking into walls.  The amp makes it to the stage and then sits still all night for the most part. Not a lot of movement going on here, so the likelihood of jarring the little solid core wires inside and causing them to snap is pretty darn slim.  Your guitar, on the other hand, is quite a different story. The guitar gets slung all over the place, smacked by your hands and hips for hours on end, and sometimes even gets used as an actual axe...or like a rock n’ roll hammer of doom.  If we had those rigid solid core wire connections inside our guitars’ control cavities, we might break them more often than would be desirable due to all the flailing about. And what about our instrument cables? Imagine if your 10-foot-long instrument cable was just one solid piece of wire and stiff as a board; not only would it break immediately, but you really just wouldn’t be able to move around very much at all.  
So, if it’s really that simple, why do we even use solid core wire at all?  Your amp doesn’t HAVE to be put together using solid wire, and if stranded is more flexible and less susceptible to breakage, why not just use stranded wire inside your amplifier too?  Great question, and the answer there is actually quite simple as well. While many amp manufacturers actually do use a fair amount of stranded wire in their circuits these days, many amp builders just prefer the rigidity of solid wire when working in such a tight space as an amp chassis.  You see, when you bend a solid wire it tends to stay exactly how you bent it; so someone building an amp could route their solid wires around obstacles in the chassis, or tuck the solid wires out of the way of other wires. The end result is often a very clean-looking build because every wire can be put in its place and never move from that place.  Stranded wires don’t hold shape that way, and when used in amps they can look messy and be difficult to work with/around. In some amps that utilize stranded wire, you may see wires bundled together and tied up to give the chassis a tidier look, but there is actually some argument here that bundling wires together will introduce unwanted noise/interference into the signal.  

Thick Vs. Thin Gauge Wire

Unlike the issue above, the fact that certain types of cables use a specific gauge (or thickness) of wire is not just a matter of preference, but is actually much more scientific. Earlier when I said, “there is a mathematical way to determine the appropriate wire to use for any given application,” this is what I was referring to.  To put it simply, thicker wire (whether the wire is solid or stranded) can handle more current. Think of it as if the wires were pipes in a plumbing system, and as if electricity were the water pressure inside the pipes. If the pipes (or wires) were too thin, they would add resistance to the flow of water, and the water would not be able to flow as efficiently.  This, in time, would put quite a bit of strain on the entire system, wouldn’t you agree?  
On a small scale, if you’ve ever put together an amp kit, you may have noticed that most of the included wire was a nice thin 22 gauge...except for the heater wires.  The heater wires in a small tube amp are typically more along the lines of 18 Gauge, and are capable of handling more current. Using a thinner gauge wire would add too much resistance to the current flow, and this resistance would lead to too much excess heat, and eventually a serious problem. 
A scenario that is probably more relatable is speaker cable.  Speaker cables need to be able to move a lot of “water pressure” from your amp to your speaker(s).  A thinner speaker cable would resist a lot of that water pressure, waste energy, overheat, and eventually malfunction.  Now, since the relative distance from your amp’s output jack to your speaker cabinet’s input jack is probably very short, it’s not as big of an issue (although using a well-made thick gauge speaker cable is always best practice).  But what about a scenario that requires a great length of cable, like routing PA speakers? Since all wire inherently has its own ampacity and resistance per foot, the longer a piece of wire is, the more resistance it creates as the signal flows along it.  As the length of wire necessary to make a connection increases, so should the thickness of the gauge of said connecting wire; the thicker wire will not have as much resistance and will have a higher ampacity rating. When speaker cables exceed 20 feet in length, they can actually cause the volume level of the source to drop by up to 5dB if they are not the proper rating for the application.  And once again, all of this extra electrical resistance translates to heat. Too much heat on a piece of wire (or its connectors) that isn’t built to handle said heat, can and will cause damage to the hardware, which can lead to further signal degradation or total failure.  
On the other hand, if you ever cut a basic instrument cable open, you’ll likely notice that the conductor wire is actually very thin — usually 24 Gauge; have a look at the image below. 

This is because the amount of electrical energy being carried from your guitar to your amp is darn small. These cables are built to take a very low voltage signal from your guitar, to your amp; once your amp gets ahold of the signal, that’s when it is boosted to a usable level.  But one major difference between thicker speaker cable wiring, and thinner instrument cable wiring is the fact that instrument cables need to be shielded. Because the instrument cable is carrying a low level signal, and because that signal is practically the start of your entire overall sound, it is imperative that the instrument cable be shielded, otherwise you could pick up radio waves and fluorescent light interference on the way from your guitar to your amp...and then your amp will AMPLIFY the interference along with your guitar signal.  Speaker cables do not require this type of shielding since the signal they are carrying is strong and has already been amplified. This is why we are all too often advised to never use a speaker cable in the place of an instrument cable. But aren’t we also told to never use an instrument cable in place of a speaker cable? Yep, not only is the thin gauge of wire used in an instrument cable typically insufficient for use as a speaker cable, but that very same shielding which protects your instrument cable from picking up interference is basically just a long thin capacitor that runs from one end of the cable to the other.  In other words, the shielding acts electrically as a low-pass filter and can remove some top end from the sound. If you are using a super-long instrument cable where you SHOULD be using a super long speaker cable, you stand to change the overall sound of your output drastically...all on accident...and THEN your hardware will break down and malfunction.

As you can see, some of these long-standing conventions came from the preference of the builder, and some of them came from a much deeper and more calculated electrical science.  But no matter the origin of the convention, it exists for a reason, and a good one at that. It is important that we as both players and as builders understand these principles because they help us understand the inner workings of our gear...and knowledge is power, people.  
We hope this article has provided some good insight as to what some of the different types of wire we use are, and why we use each type in the ways we do.  Thanks for joining us, and we’ll see you next time!