Air Compressor wiring help

[DEast]

I have a used air compressor I got a hold of. Has a 5hp 220v motor, Square D pressure switch.

The pressure switch has (5) wires coming out of it, (2) blacks, (2) reds and (1) green. I have identified which ones come off L1 & L2. These wires are in flex conduit but are not connected to anything.

The motor has three wires coming out of it. Black/Red/Green. (big wires)
In a seperate flex conduit hanging off the side of the compressor.

The 220v disconnect box (40amp, 2 fuses) I want to hook to has 3 wires in it. (1) black top post left side, (1) black top post on right side, (1) to buss bar on bottom. The box is connected by steel conduit back to the panel which is grounded at the panel.

So what hooks to what?

 

[TxDoc]

A diagram is easier (can email it). But,



motor- red------all three go to the pressure switch three connections
black---
green-----ground
from the pressure SW-----red
---green-ground-all three go to the 220v switch connections
---black
The reds and blacks go thru from the motor, thru pressure switch, to fuses on the bottom of the switch.

 

[daw53]

DEast,

You should check and make sure that the pressure switch is rated for the 5hp motor as not many are, they use a starter or contactor that is controlled by the pressure switch.

If you post the part number of the pressure switch, we can check it.

- David

 

[DEast]

The Starter / Contactor makes more sense. The wires to the pressure switch are like 12gauge and the wires from the motor at least 8 gauge. I will investigate a starter / contactorl.

 

[Aceman]

DEast, you absolutely need a motor starter.

 

[ddawg16]

If the SquareD pressure switch is a model 52, 54 or 59 then it is rated for 5HP at 230 Vac....hence, you can get by without a motor starter.

For reference, a 'typical' 5HP motor will pull 'around' 15.2 Amps full load at 230 Vac.

Here is a link to the data sheet on the pressure switch you 'might' have.

I suspect it is a SPDT switch...hence, the green is ground...the blacks will most likely be the inputs to the switches...and the red the output. Use an ohm meter...one red and hot will be shorted with no pressure...the other set will be open until you reach the pressure limit...at that point the first set opens and the second set of black/white shorts. You will want to connect the motor to the first set NC (Normally Closed). When you apply power to the compressor, the motor starts and runs until you reach the right pressure and then the switch opens shutting off the pressure.

Or, you can just pull the cover off and look inside.

The motor should have a cover plate for the power input. If you pull the cover it should have a schematic of how it is wired. Many motors of that size can be wired for either 110 or 220. You want to stay 220 if possible.

 

[Aceman]

Here we go again Ddawg! You just don't know when to quit.

1. Most pressure switches are not rated for 5 hp motors, usually only 1-2 HP at 240v.

2. He needs overload protection. I have yet to see a 5 hp motor with internal overload protection, not saying they don't exist, but I have yet to see it.

Bottom line, a motor starter is the way to go.

 

[ddawg16]

Ok....I looked in the wrong column of the spec sheet....which was why I provided a link to it. Hence, 3HP max....but this would not be the first time I have seen someone use the pressure switch to run a motor like that.

Yes, a size 1 1/2 NEMA single phase starter with overloads would be the right way to go....though I am surprised the used compressor didn't already have one....but then again, it would not be the first time someone ran a compressor like that with just a pressure switch....

Which brings up the point...you might want to check that switch....maybe replace it.

And I would double check that motor to make sure it is in fact a 5HP...what does the name plate say?

 

[W-Cummins]

Manufactures do make true 5 hp motors with built in overload protection, and put them on a compressor with only the pressure switch for control. And it's not just chiwaneese machines that are sold that way. IR has a model that is sold that way ( well I bet the pump is china made on that one...) Having said that.... I would NOT own one that was made that way. In the case of IR it's OVER priced **** instead of cheap ****, but it's **** none the less...

William....

 

[daw53]

DDawg - I think that you a little light on typical 5hp FLA (full load amps). In double checking the Baldor and Leeson catalogs, it looks like it is more in the 20-30A range for 220V single phase motors.

W-Cummins - Yes, the motor on my step-father's 5hp C'Aire compressor has a motor with internal overloads - I think that it is a Marathon. However, it does use a DP (definite purpose) contactor for the motor.

I'm guessing that starter/contactor was taken off this machine prior to DEast getting it, thus the wiring issue.

- David

 

[Greg9504]

The Starter / Contactor makes more sense. The wires to the pressure switch are like 12gauge and the wires from the motor at least 8 gauge. I will investigate a starter / contactorl.

If you end up with a magnetic starter, this thread may be of some help
http://www.garagejournal.com/forum/showthread.php?t=17044

 

[ddawg16]

DDawg - I think that you a little light on typical 5hp FLA (full load amps). In double checking the Baldor and Leeson catalogs, it looks like it is more in the 20-30A range for 220V single phase motors.

Daw53...thanks for pointing out my mistake...I went back and looked up the data...I grabbed the FLA for a 3ph motor. My bad. And thanks for being polite about it and providing the correct answer instead of just being critical like some posters are.

The actual FLA needs to come off the motor plate and will depend on what the effeciency is. Given that it's an older motor I would tend to lean towards the higher FLA.

Once again Daw...thanks for the correction.

 

[oldgraydog]

I bought an air compressor 7.5 peak hp. It is a 2002 model cambell hausfield . Its never been hooked up electrically or plumbed. It has all the tags still on it. It says no need for a external motor starter on the info tag. It shows on motor tag 21 amps. I think I am going with #8 wire 30ft. away from the breaker,with a 40 amp breaker. Does this sound ok?

 

[Charles (in GA)]

I bought an air compressor 7.5 peak hp. It is a 2002 model cambell hausfield . Its never been hooked up electrically or plumbed. It has all the tags still on it. It says no need for a external motor starter on the info tag. It shows on motor tag 21 amps. I think I am going with #8 wire 30ft. away from the breaker,with a 40 amp breaker. Does this sound ok?

This motor is somewhere in the range of 4 hp running (real hp, not that "peak" ****). In any case the 40 amp breaker on #8 wire is fine, and probably OK for the motor, given you will be seeing high starting loads. If it trips the 40 (and it most likely will NOT) it is OK to go up on the breaker size. Code allows you to upsize the breaker on a dedicated motor circuit like this to allow for starting loads. With a breaker you can go to 250% of Full Load Current if needed, and with fuses, its 175% of FLC, but thats only if you need to.

Charles

 

[oldgraydog]

Thanks Charles(in Ga.) for the info. This confirms my thoughts on this compressor. Since you should be able to use it without a external starter I suspected it was probly was under 5hp.actually.

 

[oldgraydog]

I started my compressor today and all went well I think. It only pulled 19amps. on startup.,and a bit over 14.5 amps running unloaded for about 30 minutes. Filling the tank it hovered at 19amps.Does this sound about right?Its a lot quieter than I thought it would be also.

 

[enoc11]

I to have a compressor that is a 1968 IR with a 5hp 3 phase motor upright that i am putting a 1phase 5hp on, i won this on ebay from a cummins dyno shop it is very nice i got the contact box which can be wired 1 phase but every thing was disconnected (the wiring) and i can not tell how to wire it, it has a wiring diagram inside the box for 1 2 or 3 phase it is 110 amp rating. i see where the hot lines go but cannot figure out where the ground wire goes and how to wire the pressure switch. if anyone can send me a diagram of sort to help me or if i need to provide model #s or pictures of what i have i would be happy to provide them if someone can help me. also will 8 gauge wire be good for 12ft. from 30 amp breaker thanks Greg

 

[enoc11]

sorry i forgot to ask how to post on this site that is why i replyed, idon't see anything to click on to post help thanks Greg