[TheForge] 5HP electric motor advice sought

[Dan Scheid]

-----Original Message-----
From: theforge-bounces at mailman.qth.net
[mailto:theforge-bounces at mailman.qth.net] On Behalf Of Mike Spencer
Sent: Saturday, July 26, 2008 8:41 PM
To: theforge at mailman.qth.net
Subject: [TheForge] 5HP electric motor advice sought


I need some ignorance-removal re. a 5 HP motor.  If that's nothing you
know about,  you can stop here and skip the boring details.  

I bought a 5 HP, capacitor start, 230V, (marked "23 amps" and 1.15
service factor) motor.  It has a big junction box with 4 capacitors of
one kind, two of another kind and some sort of magnetic switch.  Shaft
is 1-3/8".  I replaced a capacitor that was arcing, swapped wires
around to get the right direction of rotation.  For testing purposes,
it's hooked up:

   230V welder outlet
          |
   20' of 12 ga. wire
          |
   Heavy spring-loaded manual switch
          |
   Motor line cables

In that configuration, it starts smoothly and runs fine with no load.
But I have questions before I stick it on my compressor:

1.  Is my existing 12 ga. wire okay for 5 HP/23 amps in a 30' run?  Or
    should I have 10 ga. or even 8 ga.? The piece of line cable dangling
    out of the motor is 8 ga.
/
Sorry no 12 ga is for 20 amps and your only suppose to run 80% continually 
/


2.  Is my Square-D 9013GHG pressure switch going to work? Fuzzy
    markings inside (apparently in Spanish) seem to indicate that it's
    only rated for 3HP at 230V single-phase and 5HP 3-phase (if that
    makes any sense.)

3.  There's some kind of thing called a "starter". Do I need one?
    What does it do?  If I need one, how do I wire it up so that the
    pressure switch takes advantage of whatever the "starter" does?
    Or do I need a pressure switch that is also a "starter"?


The compressor is rated 400 PSI.  I only run up to 150 PSI and the
pressure switch cuts in again at -- I forget, 90 PSI?.  Original 10HP,
3ph motor was 3250 RPM with a 4" sheave. Present motor is 2 HP, 3250
RPM with the same 4" sheave. This new 5 HP motor is 1725 RPM and I was
planning to put an 8" sheave on it to get the same RPM at the
compressor.  This will, I'm thinking, increase the starting current in
the motor but I don't know if it's enough to matter.

I downloaded a 4.5 meg PDF from Square-D that gives every imaginable
mechanical engineering spec for 9013-series pressure switches *but
not* their current-carrying capacities or electrical specs. Feh.

Any advice or answers welcome.

Thanks,
- Mike

-- 
Michael Spencer                  Nova Scotia, Canada       .~. 
                                                           /V\ 
mspencer at tallships.ca                                     /( )\
http://home.tallships.ca/mspencer/                        ^^-^^

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