[TheForge] 5HP electric motor advice sought

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 Original Message ----- 
From: "Mike Spencer" <mspencer at tallships.ca>
To: <theforge at mailman.qth.net>
Sent: Sunday, July 27, 2008 3:40 PM
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.
>
> 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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