Air compressor help

[KMC3420]

I have an 80 gallon eaton comprssor. Bought off craigslist. Didn't know til I got it home it's 3 phase. I am in the process of converting the starter box on it to single phase. Already purchased a 5 horse single phase motor. Any body done this before in regards to the starter box. I have been told to jump one wire inside the starter box to convert it to a single phase box. Just don't want to mess this thing up. Here is a picture of inside the box.

[KMC3420]

Another pic.

[Sean1985]

That starter box is solely there for 3 phase. It looks like it has reverse phase monitor which is used to make sure that the phasing does not change and you run a motor backwards. Also has an overload protection. You don't need any of that for single phase. I would take it out if it were me.

[KMC3420]

So just take the box off and hard wire it to breaker box, and use the breaker to turn it on and off? It says inside the box add dotted line to convert to single phase. Since the 3 phase has 3 wires connected to it and the single phase has two wires coming from the motor. I assume removing the extra wire that is for the 3 phase motor and jumping the wire inside the box would trick the starter into thinking it's still running a 3 phase.

[Sean1985]

I mean you can trick the starter but to me it seems a little over kill. I run a 220v compressor at my house and I have a switch at the compressor. That starter is for protection when dealing with 3 phase. You don't ever want to run a 3 phase motor backwards and it's real easy all you have to do is switch any of the 2 motor wires. On single phase motors you would actually have to change the windings around inside the motor to turn it backwards. Or just wire like the dotted lines. That will work too. It's totally up to you.

[Sean1985]

Wire it like the diagram with the dotted line. I forgot it was a compressor and not just a single motor. It needs the starter/contactor so it will start when low on air and shut off when filled. Otherwise you will have to do some other wiring. Sorry. I'm used to troubleshooting elevator motors that start and stop.

[KMC3420]

Thanks for the help. I might have to call an electrician on this one just so I don't screw this thing up. Seems like too many dang wires to me, I am not too smart when it comes to 3 phase.

[Sean1985]

Sorry if I confused you but it's really easy. So your new motor has 2 wires that will go on t1 and t2. Your new 220v coming from your breaker will go to L1 and L2. Then take a wire and jump it from L2 to t3. It should be that simple. If something is wired wrong your only gonna trip your breaker. No biggie.

[Sean1985]

Sorry jump t3 to L3. I can't see the diagram when typing.

[KMC3420]

Okay. I thought it was that simple. Just to clarify. The diagram shows jump T2 and L3. So your saying I should jump T3 and L3.

[_Ogre]

you can't take the starter out as it controls the cycling of the compressor
the instructions are on the cover in the first pic, eliminate L2 wire, there will be no T2 wire from your new motor.
run 220v power into L1 and L3, the motor will hook to T1 and T3
last add the dotted line wire from L3 to T2 and everything should cycle correctly
you will not have a C wire, the pressure switch will go from 1 at L1 to terminal 96

you will need to check the amps on the old vs new motors and adjust the overload accordingly
post the motor tags for both motors here so we can tell you where to set the overload

[_Ogre]

this is a simplified dwg that i did for another member
you will use T1 and T3

[KMC3420]

New motor

[KMC3420]

Old motor

[KMC3420]

Overload.

[KMC3420]

I also have four wires running from my breaker box to my starter box. I see the two hots. The green ground. What about the brown wire?

[KMC3420]

Never mind on the 4 wires. The brown one is my t2 I will eliminate.

[_Ogre]

old motor running on 230 3ph, 12.2 amps
new motor running on 230 1ph, 21 amps
looking at your overload it is already set to 22 amps. so leave it alone.
if it kicks out from starting loads turn it up an amp or 2 amps.

what gauge wire is that? on what size breaker?
should only have 3 wires; 2 hots and a ground
i would run that motor on a 30 amp breaker with 10 gauge wire.
you might be able to run on a 20 amp breaker and 12 gauge wire, but you will always be maxing out the breaker and wire, you could check the amp draw with an amp probe if you have one handy
if not change the wire and breaker

[_Ogre]

the starting amps are 24, probably higher on a compressor, so i would go ahead and change out the breaker and wire to 30 amp and 10 gauge

[KMC3420]

My breaker is 50 amp and 10 gauge wire.

[_Ogre]

50 amp breaker would require #6 wire
change the breaker to a 30 amp breaker and the #10 wire is properly protected

[KMC3420]

I will have too get some wire. I appreciate the help in this. I'll let you know if I get it going.

[Daddy'O]

Question - I remember being told for a "compressor" the breaker needs to be rated at 150% to 200% of the motors starting amps. So wouldn't a 50 amp breaker be correct for this install? And wouldn't it be best to change the wire to #6 for his 50 amp breaker?

Or have I been incorrectly informed?

Thanks!

[_Ogre]

you are correct
150% would be 33 amps, i believe 30 amps would work fine. breakers will overload briefly.
wire swap to #6 would work too, but 50 amp would be a little big for the application
a 40 amp breaker and #8 wire would be ideal, just trying to save kmc some money without being dangerous

[Daddy'O]

Thanks - I needed to know if I was remembering correctly.

KMC3420 - Let us know how it goes.