My hunch is that it is probably set up with the relays inter-connected/sequenced so that while the start button is held, the small relay turns on the pony motor, and the small relay then also activates the second larger relay, which may be wired in a "self hold" once energized -so that when the button is released, and the small relay drops out, power is cut to the pony motor, but the large relay stays on, tying the larger motor to the power in/ 3ph out- and then the kill button would interrupt the larger relay's coil so that it would drop out. BE REALLY CAREFUL because it is possible that some portion of the outputs could remain live even when the relays are not actuated (before start up), or after the off is hit (after the large motor spins down). My RPC which someone (unknown exactly who) built- and designed and built pretty nicely- leaves single phase still feeding through to what should be the 3 phase output, even after hitting the off switch and the large motor has spun down- until you throw a main manual 3 pole switch that cuts everything off. Agreed with the other comment that the fuses belong in the output, and I'd recommend fusing or a breaker on the input, too. Assume nothing until you check over the whole thing, prior to operation, during operation, and after operation. Make sure any housings are all securely grounded to the safety ground (amazed how often I find DIY people didn't do that)(I am a DIY but I prefer to not have an E take the place of the Y). Even after checking over before powering up, in the beginning, the old timers' one hand rule is not a bad idea- only ever let one hand contact or come near anything (even outer housings) and keep the other hand totally away from the device and anything else conductive- that way if you contact something that turns out to be live, the shock will be localized and not pass through the main part of your body. You should be able to systematically follow the wires and sketch up a diagram of how it is set up and how it ought to behave. This stuff isn't dangerous if you are methodical and prudent, but it is nothing to mess with casually.