Larry the Cable Guys

@jea48   What I said before about 4 wires having the same inductance as equivalent 1 wire would be true if 4 wires fit in the diameter of solid 1 wire - not possible because od added insulation.  With larger overall diameter of multiple insulated strands wire inductance should be lower IMO.

Just one observation.  Thicker wire has lower inductance.  The reason for splinting wire into separate strands is skin effect.   For copper skin depth at 20kHz is about 0.5mm *  That would suggest keeping wires thinner that gauge 18.   In plain stranded wire current would jump from strand to strand (path of lower resistance - to outside) jumping thru impurities (oxides) that are on the strand's surface.  Insulating wires eliminates that, but skin effect still exist (increasing overall impedance) since strands are still in each other's magnetic field.  That is why there are strange designs, like flat cables or wires woven in helical twist on large hollow tubes, like in my acoustic Zen Satori.  Twisting and interleaving multiple hot and returns reduces inductance,   I'm not sure if skin effect is audible since most speakers are inductive at high frequencies (higher impedance), but for some speakers like electrostats (capacitive at high frequencies) it can make audible difference.

* It means that in 2mm diameter wire (gauge 12) most of electric charge at 20kHz will not flow thru inner 1mm diameter.  Skin depth is the depth where current density drops to about 1/3.  Gauge 18 wire has 1mm diameter.

@jea48   I believe that he is simply wrong.  Thicker wire has lower inductance.

Example:  2mm dia wire (gauge 12) has inductance of 345nH/ft, while 1mm dia wire (gauge18) has inductance of 388nH/ft  (not much of a difference)

As for capacitance - single wire or single pair of wires will have less capacitance than multiple wires or pairs - both overall capacitance between wires and capacitance to shield (if any).  

Inductance of the pair (cable) will be higher when wires are apart (proportional to area between them) so getting them close is important, better yet twisting them.
Twisting reduces inductance of the pair but increases capacitance.  Inductance is important in speaker wires more than capacitance so twisting is beneficial.  In addition twisting exposes wires evenly to external electric or magnetic fields reducing pickup (by cancelation).  It works fine for offending signals with wavelength much longer than the pitch of twist.  For low frequency electromagnetic interference speaker cable is too short to become effective antenna (1/10 wavelength antenna at 1MHz is 30m).

So when you parallel four 20 gauge individually insulated wires, that gives an equivalent wire gauge of 14awg wire, (15 amps), is the net inductance the same for both conductors?

Each of four individual wires will have higher inductance but connected in parallel most likely won't result in 1/4 of individual wire inductance (lower than inductance of solid 14 gauge wire) because they are in magnetic field of each other.  I suspect overall net inductance will end up the same as inductance of individual solid gauge 14 wire.  

@jea48   This cable looks good/solid.  I would interleave "Line" and "Neutral" to reduce inductance further, but it might not be practical (difficult connectors assembly).   In addition some inductance might produce filtering effect for high frequency noise.