On Wed, 22 Aug 2007 15:02:44 -0700, 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.

If the coil voltage is the same as the incoming phase-to-phase
voltage, you use a simple series circuit like this:

Line 1 In
|
Manual Off/Run switch (SPST toggle - night cut-off)
|
Pressure switch NO
|
Starter coil
|
Starter overload section cut-off NC switch
|
Line 2 In

Nobody has mentioned the overload section, and that is CRITICAL to
hook up properly on any 3-Phase machine. Pop a fuse anywhere up the
line, have a bad starter contact, loose wire - and the motor will
smoke before the circuit breaker trips.

If you have a particularly expensive motor, you want an electronic
overload section (or a separate voltage monitor) that is checking for
voltage imbalances or a phase rotation error - It's extremely rare
(since they know better) but sometimes the power utility does
overnight work and goofs with the phase rotation.

Usually it's messed up by Gomer from Jethro's Handyman Service that
doesn't understand the concept of Phase Rotation and just stuffs the
wires together in any old order. Git 'Er Done!

-- Bruce --