Now it gets truly fascinating! Pictures of MCBs clearly marked "FPE StabLok" but mounted to a DIN rail and with line-side screw terminals and wire jumpers instead of bus bars!

https://scontent-vie1-1.xx.fbcdn.ne...2d6c493f3471ff1654c680cf&oe=5A9AC118

Note the loose unused cable on the left. The three 40 A breakers (bottom-right) seem to serve as splice blocks, I don't see anything connected to the load side. Another truly crazy install!

Here's a closer view:
https://scontent-vie1-1.xx.fbcdn.ne...4788203eabd5a44fda06fb0d&oe=5AAA5879

Now we've got the most common trip curves of the day, H (for household circuits, e.g. lighting and sockets in high loop impedance TN supplies, very fast-acting magnetic trip), L (for general lighting circuits, short-circuit trip identical to modern B) and G (very sensitive thermal overload and generous short-circuit trip, designed for high inrush currents). 40 A wasn't a standard size at that time though, only 35 and 50. The plot thickens!