Contactor wired correctly?

[Owen]

Hi all,
I finally got around to getting a contactor for my air compressor. The primary reason was to be able to use a wall switch to turn it on and off as the compressor is mounted in a closet. Compressor is a Husky 60gal 230V. Previous thread
http://www.garagejournal.com/forum/showthread.php?t=48938

I bought a Fuji contactor SC-E5 240VAC. Do I have this right? Should the ground wire be going straight through or should I leave it connected to the bracket mounted to the compressor for the pressure switch?

Something doesn't seem right...is the pressure switch purely mechanical and does not need the LINE INs connected?

Thanks!

 

[trainer]

your pressure switch should have an unloader valve that lets the pressure off of the compressor head when it cuts out or is switched off. THis setup bypasses that.

Also, the ground should not be switched.

Why not just leave the compressor on?

 

[tdkkart]

your pressure switch should have an unloader valve that lets the pressure off of the compressor head when it cuts out or is switched off. THis setup bypasses that.

Why not just leave the compressor on?

The unloader portion of the pressure switch is a mechanical function, as long as the pressure cycles the switch the unloader works, doesn't matter how the switch is connected electrically.

As soon as I get the new pump installed on my compressor it will be connected in a similar fashion. When I wired my shop I included a connection in one of the lighting circuits to do just this function, if the lights are off so is the compressor.

I have had 3 failures that have caused my compressors to run unattended continuously. IMO leaving a compressor turned on and unattended is a dangerous and potentially expensive situation that i do not want to deal with. This small modification will add another automatic protection.

 

[GeorgiaHybrid]

Why are you switching both legs to the pressure switch? I'm assuming you will have a single 120v line that is used to trigger the mag starter but I would just switch the input side of the pressure switch. That will kill any power to the contacts and should still work the way you want it to.

 

[JBurgess]

I couldn't find a speec sheet on the model # you posted, but from using the generic wiring from page 8 here:

http://www.automationdirect.com/static/specs/fujimc9150.pdf

I get this:

 

[Owen]

your pressure switch should have an unloader valve that lets the pressure off of the compressor head when it cuts out or is switched off. THis setup bypasses that.

Also, the ground should not be switched.

Why not just leave the compressor on?

Basically, I don't use it every day. So I don't mind the couple of minutes to fill it up when I do need it. Also, I hate when it runs in the middle of the nite.

 

[Owen]

Why are you switching both legs to the pressure switch? I'm assuming you will have a single 120v line that is used to trigger the mag starter but I would just switch the input side of the pressure switch. That will kill any power to the contacts and should still work the way you want it to.

This is another part I'm confused on, the coil is 220V and I thought the single 120V line to trigger it wouldn't work. I realized this when I opened the box and wondered whether I should have gotten the 120V contactor?

 

[Owen]

I couldn't find a speec sheet on the model # you posted, but from using the generic wiring from page 8 here:

http://www.automationdirect.com/static/specs/fujimc9150.pdf

I get this:

So I would not use A1 at all? Interesting...why does A1 need to be connected to L1 then? Or do you mean that is the pressure switching aspect of it?

Also, does this mean I will have 240V on A1? And when I close the switch, it completes the circuit and allows the contactor to switch?

 

[Owen]

Thanks everyone, for your help!

 

[JBurgess]

So I would not use A1 at all? Interesting...why does A1 need to be connected to L1 then? Or do you mean that is the pressure switching aspect of it?

Also, does this mean I will have 240V on A1? And when I close the switch, it completes the circuit and allows the contactor to switch?

A1 and A2 are the connections to the coil. It needs 220V to energize the relay. A1 connects to L1 . A2 is switched by both the light switch and the pressure switch, it gets it's power from L2. L1 to L2 is 220, so when both the light switch and the pressure switch are on the coils sees 220V. If either ths light switch or the pressure switch is turned off, the coil sees no voltage.

Be sure your switch is rated for 220V.

 

[Owen]

Thanks for the quick reply! This is what I'm not getting.

...A2 is switched by both the light switch and the pressure switch, it gets it's power from L2.

Are A1/A2 on the pressure switch side connected? I guess I can confirm with a DMM. It sounds like I should be bringing one phase to each side of the pressure switch outputs (Motor).

And I am NOT bringing L1/L2 to the formerly used Line terminals of the pressure switch, correct?

 

[JBurgess]

Does this help?

 

[Owen]

I think so, it would probably make more sense if I was in front of it instead of at the computer.

Again, thanks for your patience in helping me out!

 

[mad57]

i would not run the main line to the pressure switch,just to the breaker where L1 AND L2 ARE. THEN YOUR LINES OUT TO THE PRESSURE SWITCH ON MOTOR AND LINE.

 

[Owen]

I went through an old bookmarked thread and found the following, which (seems to me) matches JBurgess drawing on the right.

"Any way, in a compressor application the contactor coil is wired in series with the pressure switch. One side to the pressure switch line terminal ( from an allways hot, line in, from the starter ) and the other wire to the pressure switch motor terminal conects to the contactor coil. The other side of contactor coil is to the grounded conductor if it's a 120v coil or to the other line in hot if it's a 220V coil. So that when the pressure switch is closed ( low pressure) current flows to the coil on the contactor and the compressor runs until the pressure builds up and opens the contacts of the pressure switch, then the current is cut to the coil and the mag contactor opens and turns off the motor...."

http://www.garagejournal.com/forum/showthread.php?t=22949

Now what size wires should I be using to connect the L1/L2 to the contactor coil?

 

[Owen]

i would not run the main line to the pressure switch,just to the breaker where L1 AND L2 ARE. THEN YOUR LINES OUT TO THE PRESSURE SWITCH ON MOTOR AND LINE.

I believe that is what J Burgess' red lines in my picture shows. The pressure switch is just tapped off the L1/L2 source.

Do I need to splice the wires or can I just cinch down the tap wire in the L1/L2 terminals (screw in, clamp down type)?

 

[JBurgess]

Do I need to splice the wires or can I just cinch down the tap wire in the L1/L2 terminals (screw in, clamp down type)?

The spec sheets lists the terminals for 1 or 2 wires so just cinch them down.

Wire size? What size circuit is it on?

 

[Owen]

It's on a 30A circuit, with #8 conductor and #10 ground from the plug to the compressor. Don't know what's in the conduit, electrician did that.

Just looked back at the pdf link earlier in this thread, pg 5, looks like it gives max sizes for the main and control circuits. Two #10 max for the control, is that bigger or smaller than one #8 and an #18 for the pressure switch?

 

[Owen]

On page 6 of the pdf, what are top only, bottom only, and top/bottom?

 

[Aceman]

It looks like JBurgess is steering you straight. I can't see how you're going to be able to add a wall switch in series with the pressure switch without fusing it down. Since you're on a 30 amp circuit, it's not legal to run anything less than 30 amp wire off this circuit and over to a wallswitch box unless you fuse the control circuit down.

I usually add a control fuse holder right inside the contactor box and throw a small 5 amp fuse in it. Tap off the contactor (L2) with #14, #12 etc run through the control fuse, then to your wall switch, back to the pressure switch, and then to one side of the contactor coil(A2). Power to (A1) is tapped right off the #8 you said was feeding (L1) and is not switched at all.

 

[Owen]

Thanks Aceman,
Would it help if the wall switch was 30A rated?

And does it matter if the switch is ahead or behind the pressure switch?

 

[Aceman]

I don't have time to look it up right now, so to be on the safe side I'd say you'd have to run 30 amp wire(#10) to a 30 amp switch.

It shouldn't matter if it's before or after the pressure switch.

 

[JBurgess]

That type contactor usually has a screw with a square plate and is intended for 1 wire on each side of the screw like this:

#8 is bigger than #10.

Did the contactor come with an enclosure and are you mounting it to the wall or the compressor? A picture of the contactor might help.

Is light switch being mounted to the wall?

As been said without additional fuses #10 wire should be used. It should also be stranded if it is subject to vibration.

 

[Owen]

That's pretty much what the screws look like, picture of the unit can be seen in the PDF linked earlier.

I didn't know if I needed an enclosure or not, so I will just mount it and the switch to the wall. My cold is finally going away so hope to get it done this week, still have a new computer to build too...sigh.

 

[JBurgess]

I didn't know if I needed an enclosure or not, so I will just mount it and the switch to the wall. My cold is finally going away so hope to get it done this week, still have a new computer to build too...sigh.

You will need an enclosuere for the contactor as well as a box to mount the switch in.

 

[Owen]

Gotcha, thanks again.

 

[Stephenw]

 

[Owen]

Well, got it all wired up and it wouldn't work! So I reversed J Burgess' last drawing so that L2 was jumpered to A2 and L1 had a tap going to the P switch and light switch, and it worked. Not really sure why, but who cares!

 

[Owen]

One thing that confused me was that there was 120V on A1 and on A2, even with the switch off or physically removed from the wiring. And if IIRC, even when I had no wires coming from the pressure switch. But, A1 to A2 did not equal 240V, it equaled 0V. If I knew how to read the included electrical diagram better might make some sense.

I still need to wire in a light to let me know at a glance if the switch is on or not.

 

[GeorgiaHybrid]

Owen,

You are measuring from A1 or A2 to ground. These are 240 terminals and act as a ground to each other on opposite cycles. If you put 120v to each terminal on opposite phases, the mag switch will work correctly. It seems crazy if you are used to 120v only but it is correct.

 

[Owen]

Owen,

You are measuring from A1 or A2 to ground. These are 240 terminals and act as a ground to each other on opposite cycles. If you put 120v to each terminal on opposite phases, the mag switch will work correctly. It seems crazy if you are used to 120v only but it is correct.

Very crazy, I'm only used to 12V on cars!