[jyl]

I have an appliance (espresso machine, not the same one that I've previously posted about). It has five wires in the cable: black, black, brown, blue, green/yellow.

It came with a 240v 30A twist lock, 3 prong plug and was wired as follows :
- green/yellow wire to ground prong
- blue wire to a hot prong
- both black wires and brown wire together to other hot prong

The manual for this machine says
- green/yellow is ground
- blue is neutral
- black, black, brown are the three phases

The manual also says the machine can be connected to 240v single phase power "without modification". "hook up the ground and neutral wires to the two respective terminals on the electric switchboard. Join up the three wires of phases 1, 2, 3 together and connect them to the single terminal of the phase present in the electric switchboard". It also says a plug may be used.

I have to replace the existing plug with a 240v 50A 3 prong plug. 6-50R type.

I think I connect the new plug as follows:
- green/yellow to ground prong
- blue wire to a hot prong
- black, black, brown wires together to other hot prong

Basically I'm copying how the existing plug is wired and it sounds consistent with the manual.

What I'm trying to understand is why does this work. Why is the machine okay with all three phases being wired together? How does it "know" if it is wired to 240v single phase or to 400v triple phase?