He is arguing, because he thinks that we're saying the energy usage is 1/2 on 240 than it is 120, and no one here that I can see is claiming that.
Crap, you're right, that is where the disconnect is, and I'm totally reading and interpreting all the math wrong as a result. The amperage would indeed be the limitation on the breaker box.
I mean, technically you COULD still install 4 20a 110s in a breaker box fed by a single 40a 220, but you'd still have the load problem and the breaker would trip under more than 50% load, and that wasn't what I was saying anyway. Apologies for confusing the conversation.
4 20 amp 117 circuits fed from a single 40 amp 234 circuit WILL NOT cause your breaker for the 40 amp circuit to trip at 50% power draw, unless you don't wire the 117 circuits correctly in the secondary panel.
The way the panel is set up, 2 of those 117 circuits end up IN SERIES with the other 2 (with the neutral transferring any imbalance back to the pole transformer) IF you wire the thing up correctly, 2 breakers on each "side".
For reference, common 234 volt service in the US (and Canada) is set up as "split phase", more widely known as a "center tapped" arrangement.
Half of the 117 circuits are set up to be on one side of the "neutral" center tap, the other half on the other side, with the WHOLE of each side being in series with the WHOLE of the other side, optimally keeping the draw on each side balanced or nearly so to reduce the current on the neutral feed line.
THEREFORE, you can pull *TWICE THE AMPERAGE* at 117 as your 234 feed provides, as half that amperage is in series with the other half.
This is not theory, this is a union-trained electrician and a VERY long time electronic tech explaining FACTS.
That's what I thought initially. Thank you for clarifying, that makes total sense (and I KNEW my math was right!).
