wrote:

How do you connect a 2 wire pressure switch for an air compressor to
a three phase magnetic motor contorller (siemens)? Do both wires
connect to the coil? Does one wire connect to the power and the other
connect to the coil? Three phase power is via a phase converter.


You need a little book called Ugly's Electrical References. However, if you
had it, you wouldn't be asking, so here's the relevant wiring diagram:
http://www.tinyisland.com/images/tem...sHOAwiring.jpg

Normally an air compressor has a Hand/Off/Auto switch. Note that in this
diagram, the little red ellipse that says 'M' inside is the magnetic coil.
Leaving out the fuse and the HOA switch, then the pressure switch is
indeed connected in series between one hot (power) wire and one side of
the coil, and the other side of the coil (which must be rated for the
correct voltage - this is critical) should go to the second real hot lead.
What I mean by that is that your coil should be connected in and out between
the two legs which comprise your single phase power, not the 3rd leg generated
by the phase converter.

Grant