1st post...
As perhaps an upper extremes data point I can offer on internal speaker cabinet wiring, I was just inside my PA systems pro audio subs; the EV MTL-4 manifold technology cabinets, each containing four EV DL18W 18" speakers. The cabinets are rated at 1600w RMS per the EIA RS-426A long term power handling standard, and 6400w per 10ms peak.
Metallica only needed 20 of these cabinets in their punishingly loud 1990s arena tours...
Sound Pressure Level at 1 Meter, Indicated Input Power,
Anechoic Environment, Band-Limited Pink-Noise Signal.
50-200 Hz,
1 Watt: 102 dB
1600 Watts: 134 dB
6400 Watts: 140 dB
The details of the EIA Standard RS-426A test as EV applied it to these subs was this: "The EIA test spectrum is applied for eight hours. To obtain the spectrum, the output of a white noise generator (equal energy per bandwidth in Hz) is fed to a shaping filter with 6-dB-per-octave slopes below 40 Hz and above 318 Hz. When measured with the usual constant-percentage analyzer, (one-third-octave) this shaping filter produces a spectrum whose 3-dB-down points are at 100 Hz and 1,200 Hz with a 3-dB-per-octave slope above 1,200 Hz. This shaped signal is sent to the power amplifiers with continuous power set at 800 watts into each of the 3.45 ohms EIA equivalent impedance inputs (52.5 volts true RMS), (my note: the four speakers are grouped into pairs, so there are two speakers per pair of Speakon connector contacts)
resulting in a total of 1600 watts of continuous power being delivered to the MTL-4. Amplifier clipping sets instantaneous peaks at 6 dB above the continuous power, or 6400 watts peak (105-volts peak per input). This procedure provides a rigorous test of both thermal and mechanical failure modes."
They use Essex Royal 14 gauge Copper stranded wire type MTW 105 degree C 600v throughout... and the wires sure didn't melt, (-better not; these can be flown cabinets!) -nor did they shake apart. The insulation shows no signs of discoloration or embrittlement either, so it would appear that EVs engineering was proven sound... my speakers are in excess of 20 years old, with previous owners who were far less respectful of their ratings than I.
14 gauge gets the job done in those cabinets you see flying over your head.