Air compressor wiring help

[70-K5]

Picked up a BRA618A compressor. It's a 6hp baldor motor, Ingersoll-Rand 2340 pump. 80 gallon tank.

I have a smaller 3.5hp 60 gal U.S. General compressor that works fine, but this was a good deal.

Someone wired the presure switch to a 120 plug, and removed the wiring from the pressure switch to the motor, not sure what they were thinking.

Motor has two capacitors that I can read the part number and a third that is silver that I can't read the numbers on it.

Before I haul it into the mechanics at work, anybody help me out with how to wire this?

 

[The Cobbler]

Can't help with the wiring but the plug looks like a 50 amp 240 volt plug . and it will be noted that is not rated for a 7HP motor

need pics of the motor plate & wires in the box

 

[cvairwerks]

Above 5 hp needs to be on a mag starter too.

 

[70-K5]

I don't think this came with a magnetic switch, I'm looking into what is missing though.. searches tell me that the right high amperage pressure switch won't need the mag switch?

Motor is thermaly protected, has the two starting capacitors and the single run capacitor. I haven't wired those and that is where everything is getting a little new to me. I have wired compressors before, did the whole 120/240 iny shop, but I don't have schematic for the whole motor..

 

[The Cobbler]

I doubt if you'd find a pressure switch that is rated for the amperage of that motor without using a mag starter
what it had, what it came with when you got it, and what it needs are all up for discussion

 

[Jswain]

White & black from the wall will both go to line on the pressure switch, so move black from where it is now to above the white assuming those are both coming from the wall...as it is right now when the switch closes you are connecting white & black from the wall to each other

Then run a black & white from motor on the left of the pressure switch to the side of the motor to L1 & L2. If you haven't touched any of the wiring on the capacitors it is likely ok. Make sure you check rotation of pulley when you get it spinning

Motor is thermally protected so you don't "need" a magnetic starter but it would take the load off the pressure switch. If it fails and welds itself closed then the compressor will run continuously. If it is rated for continuous duty it might be ok. If your safety valves fail as well you might blow the compressor through the roof of your garage.

Agreed plug should be removed and hardwire the compressor but for testing and the prove it works/troubleshoot I would run it as is if you already have a welding outlet, if not don't waste your money on a receptacle either go right to the breaker or to a disconnect.

 

[cvairwerks]

Motor is thermally protected so you don't "need" a magnetic starter

I’ve yet to see a pressure switch on a compressor that is rated for anything greater than 5 hp. Outside of a few manufacturers, most use motors that are only alleged to be 5 hp. Every one I see that has an actual 5 hp or larger motor does have a mag starter on it.

 

[mark-NJ]

The pressure switch needn't be HP rated. On a motor of this size, it's job is to turn off the magnetic contactor by interrupting the coil voltage. In other words it's rated for the control circuit's current, not the motor's current.

And, yes, a magnetic contactor is required. The thermal protection internal in the motor has nothing to do with STARTING the motor.

 

[Jswain]

Sure a magnetic starter would be better, but on nearly all 5hp compressors with thermally protected motors you will not see them.

They come straight from the factory like this...

 

[mark-NJ]

Well, ok..."apples & oranges".

"Specsmanship" strikes again. The motors in the pictures posted above may SAY 5HP, but those are *NOT* 5HP motors. Not even close.

The whole marketing thing about "Horsepower = determining torque, dividing by amps, multiplying by your locker number, raising to the square of your hat size, then dividing by you street address" runs rampant in many industries where the motor is integral to the final product. Those 2 compressors in the posting above this one are no way 5HP motors.

By contrast, the OP's photo is, indeed, a 5HP motor (though it shows 6HP definite purpose), and the current draw (26A @240V) confirms such. THAT motor most certainly needs a contactor. No question about it.

 

[Jswain]

Baldor makes 5hp thermally protected motors that do not require magnetic starters...

 

[cvairwerks]

Baldor makes 5hp thermally protected motors that do not require magnetic starters...

It's not the motor that is the problem, but the pressure switch. Pull up just about any air compressor pressure switch and look at the ratings for it. Most are only rated to switch 3 horsepower and under. Square D makes some that will, and I'm sure others do too, BUT you have to start running 460VAC to get to a 5 hp rating.

 

[mark-NJ]

Baldor makes 5hp thermally protected motors that do not require magnetic starters...

5HP @ 240V (single phase) draws about 28A with an inrush of about 150A (assuming not starting against head pressure). Without a contactor, what switch do they suggest using to turn such a motor on? Bottom line, the contacts of whatever switch is selected needs to handle that current, and I can't think of ANYTHING, besides a contactor, that can do such.

What am I missing?


EDIT:: wait...I think I'm "seeing" it. A "Motor Starter" is a contactor + a thermal overload. Is Baldor saying that, "...because we have internal thermal protection, then a motor starter (i.e. "overload protection on a contactor") isn't needed..."? Is that it? You could do without the overload, but you'd certainly still need the contactor.

 

[Jswain]