you lost me. Revising, a clean unclipped sine has 0.71 of the peak as it's RMS value, half the RMS watts so are you saying an honestly rated amp would be no more than 150w and there is a bit of marketing fudge around the ''continous'' 200w of the ELF if it doesn't need speakon?
Specifically, it's the voltage above or below ground, accessable with respect to ground. So, for amp that is BTL and swings 35 volts peak above ground (I'm using the BTL as the example because it's become the most common, though not exclusive, topology for the smaller lightweight amps), as the voltage swings above ground on the tip it swings equally negative below ground on the sleeve of the jack/plug. The following does not apply to non-BTL topology amps.
The rough calculations for BTL only would be:
peak-peak = 2 x 35V peak = 70V peak-peak
RMS = 70 x .707 = 50V RMS
Power = V**2/R = at 4 ohms for 50VRMS = 625 watts (
in practice it would be about 15-20% lower due to losses and unloaded hi line testing reqts. making 500 watts the practical limit for BTL)
But (and this is the elephant in the room) some jurisdictions consider the tip terminal inside the 1/4" jack to be accessable because of the touch-probe test to a adjacent speaker plug's shell so in this case the 35V would apply to the tip to sleeve voltage and 35 volts peak only would apply, thus the RMS voltage under this jursidiction would be 35V x .707 = 25 VRMS and the power at 4 ohms would be 150 watts. With 2 jacks, this is a plausable issue but pmore likely not with 1 jack.
The problem is in how strict and literal the inspectors interpret the code section, because the code is literal but the interpretation is not... and different countries interpret things differently too. Most of the safety agency engineers that I have worked with over the decades have been of the more strict variety, which is understandable since the whole idea of the regulations is to improve public safety... and they are getting stricter all the time. Because of this, I personally tend towards being conservative as that is the inspector friendly course. Nobody wants to piss off the inspector, an important lesson best learned as a young lad.
Engineering is not always an exact science. This is taught over and over again in school, and it's most easily demonstrated in the mechanical engineering world by having a cooridinate system that is not static but moves and spins with its own set of equations that describe its motion. If the coordinate system moves through space exactly the same as the object being studied, the object is standing still WITH RESPECT TO THE COORDINATE SYSTEM, and somebody standing on that coordinate system will swear that the object is not moving yet the person who is standing on the static coordinate system is certain that the object is moving.
I went through this example to show how difficult even the simplest appearing issues can be.
