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Thread: Eaton Mag Starter + Compressor Wiring Question

  1. #1
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    Eaton Mag Starter + Compressor Wiring Question

    I have a new Quincy QT-54 5HP (230V 1P) air compressor and I am adding an Eaton 5HP 230V magnetic motor starter (Eaton model# B27CGF30B040) to it.

    I want to make certain I am wiring it correctly, so if you can verify (or correct) my plan it would be appreciated.

    The setup:

    I have a dedicated 30A breaker (#8 wire) circuit pre-wired to a wall-mounted, non-fused disconnect. From this disconnect I will bring 2 #8 hots and 1 #6 ground wire into the Eaton box.

    One hot will go to lug L1 the other to lug L2. The ground will connect to the ground bus bar I will be installing (depicted as the green stripe for now). The yellow dial will be set to 30A.

    The motor will be wired to lugs T1 and T3 with it's ground also going to the new (green) ground bus bar. I already moved the motor wires from the pressure switch up to the Eaton starter.

    The one thing I am not certain about is which lugs on the top of the Eaton device I use for the pressure switch to trigger the motor?

    My continuity tester showed that I use just one side of the mechanical pressure switch, for example side (A), but then do I connect these wires to the two top, rear connectors in the Eaton box, the silver one behind L1 and the brass one behind L3? I'm about 99% sure this is correct.

    Thanks for your help.

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    So now SPECIFICALLY which tabs do I run the wires from the pressure switch up to the top of the Eaton?

    L1 Rear (silver)
    L1 Front (silver)
    L2
    L3 Front (silver)
    L3 Rear (brass)

    Let me know which two please, that's the simple answer I need.
    I know that it is not the two front L1 and L2 (silver) tabs so I am assuming it is Rear L1 and Rear L3?
    Last edited by LuMax; 06-10-2015 at 10:30 PM.

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  3. #2
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    Re: Eaton Mag Starter + Compressor Wiring Question

    I can't read your magnet coil voltage. If it is 230 volt rated, power comes from L2, down to 95, passes through contacts to 96, then up to one side of your coil. 95-96 is your overload relay. It controls the motor by making or breaking the circuit through the contactor magnet. A conductor is needed to bring power from L1 to the pressure switch. Another will bring power from the pressure switch to the other side of your contactor magnet at the top. I'm confused by the heavier conductor from L3 to T2. Why is it there?

    The leads on your pressure switch now interrupt motor load. When using a contactor/overload relay, this switch loop is not needed. Load conductors will go straight from T1 to Motor L1, and from L2 to Motor L2. If you have a two voltage motor be sure it is wired to supply voltage.
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    Re: Eaton Mag Starter + Compressor Wiring Question

    The Eaton box shown was wired that way from the factory. It is a 3P box being set up for 1P. Every setup I have seen (and I did a lot of reading) shows the line voltage setup as I described above: they connect at the top to L1 and L2. The ground goes to the bus bar.

    Then, the motor is connected to T1 and T3 at the bottom. It's ground also to the bus bar.

    The line voltage is not connected to the pressure switch (as the compressor was set up for), and the motor wires are moved from it and placed at T1 and T3. This way the pressure switch merely sends a closed circuit (low tank pressure) signal to the starter to close the contacts and start the motor.

    The question is which two tabs the pressure switch gets wired to?

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    Re: Eaton Mag Starter + Compressor Wiring Question

    Pressure switch goes L1, and contactor magnet behind L1. The pressure switch is a double pole switch, you will use only two terminals to interrupt power from L1 to one side of the magnet. The overload relay 95-96 interrupts power from L2 to the other side of the magnet. As the magnet requires a complete circuit, (both legs of a 230 volt supply) either of the switches in play can interrupt the circuit for the magnet, stopping the motor. The heavy contactor serves as a three pole switch controlled by the magnet. L1 powers T1, L2 powers T2, If it were 3 phase, L3 would power T3. It appears to me there is a jumper sending power to L3 from T2 which is only live when the motor is running. I don't think this is harmful except there then will be too many conductors trying to share T2. If instructions tell you to use T3 for load, they may do this to send motor load through all overload circuits to sense motor current. This is practice I haven't seen in 45 years of motor controls. Check your instructions. This needs also a 30 amp breaker, and a means of manual disconnect within sight of the motor. This disconnect could be a receptacle and cord.

    Eaton may give settings for motor overload settings. Space in the enclosure will affect this setting if it uses heaters. If you have no other instructions, I would start at motor full load. I prefer replaceable melting alloy heaters as it's too easy to turn up the load tolerance when motor is overloaded, causing motor failure.

    Confirm your magnet is for 230 volt.
    Last edited by Willie B; 06-11-2015 at 09:07 AM.
    An optimist is usually wrong, and when the unexpected happens is unprepared. A pessimist is usually right, when wrong, is delighted, and well prepared.

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    Re: Eaton Mag Starter + Compressor Wiring Question

    Your contactor is wired correctly. T1 and T3 to the motor. One wire from L1 to the pressure switch and return from the pressure switch to the coil connector behind L1. You do have a 208-230 volt coil according to the Eaton website. Just use the front and rear connections on the same side of your pressure switch. Leave the other two unused. In other words, use the A side or the B side front and rear.
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    Re: Eaton Mag Starter + Compressor Wiring Question

    I'm just curious why you've gone to the added expense and complexity when the factory pressure switch is rated for and perfectly capable of controlling the motor for years?
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    Re: Eaton Mag Starter + Compressor Wiring Question

    Thanks Willie B and hdonly0.

    I got the Eaton for an incredible price, and I prefer to remove the 30A 230V line power from the pressure switch and just use it as a low current switch. All of Quincy's bigger or more expensive compressors use a magnetic starter. Also the Eaton adds a layer of safety.

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    Re: Eaton Mag Starter + Compressor Wiring Question

    BTW, you wouldn't happen to be the "Willie B" who was on the rock station back when I lived in Denver are you?

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    Re: Eaton Mag Starter + Compressor Wiring Question

    I just finished installing my QT-54 today. Here you can see the Eaton Mag Starter along with the Hobbs Meter I installed. Also on top is an intake muffler attached to the filter housing.

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    There was a lot of noisy vibration between the belt/fan guard and frame so I added a layer of thin, dense rubber between all of the contact points. It eliminated all of the vibration noise. I also added custom corner brackets to the cage that made it much stronger.

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    Here is the Tsunami bottom tank drain setup:

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    Also, the Tsunami drain for the after-cooler. Not pictured is the fan shroud that I built for the EBM-Papst fan to AKG cooler:

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  13. #10
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    Re: Eaton Mag Starter + Compressor Wiring Question

    Quote Originally Posted by LuMax View Post
    BTW, you wouldn't happen to be the "Willie B" who was on the rock station back when I lived in Denver are you?
    Nope, I did go out west once, got as far as Granville NY. Things seemed to be getting worse instead of better, so I turned back.
    An optimist is usually wrong, and when the unexpected happens is unprepared. A pessimist is usually right, when wrong, is delighted, and well prepared.

  14. #11
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    Re: Eaton Mag Starter + Compressor Wiring Question

    By the way, your intake is driving me crazy. I feel it breaking! if it's only the threaded pipe near the head, no big thing. If it's the head, that's a bigger deal.
    An optimist is usually wrong, and when the unexpected happens is unprepared. A pessimist is usually right, when wrong, is delighted, and well prepared.

  15. #12
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    Re: Eaton Mag Starter + Compressor Wiring Question

    Don't worry about it. That is galvanized pipe and the muffler is light. Very little vibration up there also. It did quiet the intake down though so it stays since I have neighbors that I like being nice to.

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    Re: Eaton Mag Starter + Compressor Wiring Question

    How do you turn this beast on and off? I don't see a start stop station attached to the starter.

    Sent from my SAMSUNG-SM-G900A using Tapatalk

  17. #14
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    Re: Eaton Mag Starter + Compressor Wiring Question

    The Auto/Off switch is on the side.

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    The flexible water-tight (gray) line is connected to a wall mounted, non-fused disconnect (the dedicated compressor circuit is already protected by a GFCI breaker) used when servicing the compressor.

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    Last edited by LuMax; 06-13-2015 at 03:11 PM.

  18. #15
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    Re: Eaton Mag Starter + Compressor Wiring Question

    Can you post a final pictures of your Eaton Magmetic Starter wiring setup along with the pressure switch? Im configuring a new Quincy QT-54 the same as yours. Thank you!

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    Re: Eaton Mag Starter + Compressor Wiring Question

    Quote Originally Posted by AxTrader View Post
    Can you post a final pictures of your Eaton Magmetic Starter wiring setup along with the pressure switch? Im configuring a new Quincy QT-54 the same as yours. Thank you!
    Hi, I was wondering if you got your Quincy wired up yet? I am currently swapping my 3 phase motor and 3 phase contactor to a 5 hp single phase motor and single phase contactor. The contactor is an Eaton 30 amp definite purpose contactor. I also wanted to know where to connect the two leads from the pressure switch. Thank in advance.

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    Re: Eaton Mag Starter + Compressor Wiring Question

    Quote Originally Posted by Bzeis View Post
    Hi, I was wondering if you got your Quincy wired up yet? I am currently swapping my 3 phase motor and 3 phase contactor to a 5 hp single phase motor and single phase contactor. The contactor is an Eaton 30 amp definite purpose contactor. I also wanted to know where to connect the two leads from the pressure switch. Thank in advance.
    One end of the contactors coil goes to one 120 volt leg of the power.

    The pressure switch is powered with the other 120 volt leg that feeds power to other end of coil.

    Pressure switch closes and the coil gets 240 volt.

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