electrical
With the main house breaker turned off, I have electrical continuity between the hot lug at the service entrance and the neutral bus in my service panel.
I also have electrical continuity from neutral to one leg of the service.
Does this indicate that I have a bad main breaker?
I think you may be over-thinking this. You can make a connection on either bus without reaching across an ungrounded bus in that panel.
The ground and neutral bars are so located as to give you free access to them without have to reach around or near an energized bus. You could stand to the right or left to make your connections without reaching across the phase bus.
In a larger piece of switchgear, the phase conductor bus should be located further in and the ground and neutral bars closer to the access panel not the other way around.
I think that is the intent of the code.
Don't the two hot legs need to be balanced if it's line to line to compensate for the fact that there's no neutral?
No, if there is no neutral then all the loads must be connected across phase to phase. In US terms this would mean that there are no 120V loads that need to be balanced.
I'm not convinced you have two hot legs from a US style split-phase supply.
The Chinese standards seem to be pick and mix of other countries standards. Note that Red=Live, Blue=Neutral, Green/Yellow=Earth is a valid colour combination in Australia.
The four "two-pole earth leakage breakers" (tengen DZ47LE-32 C16) are marked with N for Neutral at one connection.
I would therefore, naively perhaps, expect the blue wires to be neutral and to have zero or very low voltage with respect to the green/yellow ground wires.
I don't see any normal bus connectors, it seems the installer used red wires to construct buses live and instead of the neutral terminal that would be found in a UK consumer unit.
CE marked C16 circuit breakers should be 16A breakers with a "normal" sensitivity range.
The blackening of the top screws of the old breaker is also concerning. Is too much resistance on the wire or screws/breaker a possible cause?
The clamping screws were not done up tight, the cables were not inserted correctly or the switch was passing too much current. Or all three.
Example, for comparison purposes, of an old and unusually neat UK equivalent showing copper bus bars at bottom connecting live feed to single-pole breakers, terminals at top for neutral and ground (these terminals are sometimes also called bus-bars). Note the copper bus bars normally have a plastic shield, and normally there is a cover that shields all the wiring with holes for access to the breakers only.
Since China is not the UK, there may be entirely different exemplar Chinese installations that bear little relation to this. The question shows an installation where every breaker and switch has two poles. This means there is no need for a neutral terminal connector strip. However the neutral wires linking adjacent "earth-leakage breakers" form an improvised bus.
Best Answer
Since you are not connected to the grid yet, the wires from your mast a probably just hanging or coiled up, and the ends are touching. Check those wires.