Problems wiring my Kobalt compressor

[Red Lion]

I recently purchased an 80 gallon Kobalt 4.5HP compressor. It was running at the seller's home, he had it wired in his garage directly to the breaker box, using 10 gauge wire. It ran for a good couple of minutes.


I took it to my shop, which has 220 single phase wiring. I wired it up using a 3-wire, 50 amp, 250volt plug (same type I use on my milling machine). It never quite ran right, like it wasn't getting enough power to go full speed. Then, the speed would rise and fall, rise and fall, etc. Lastly, while trying to solve the gremlins, it wouldn't even rise, it would just sputter. Sometimes it would trip the breaker, sometimes not.


The outlet it goes to is a 220 attached to a 20-amp breaker. I thought maybe, since this compressor is meant to run at 18amps that it was nearing the limits of the 20-amp breaker, so I swapped that out to a 30-amp (the wiring to this breaker is all 10-gauge). The plug is good and the outlet too, I use this outlet for my milling machine and welders.

Still nothing, it wouldn't get any speed. I began playing with the wiring, thinking maybe I had wired it wrong. I switched some wires around and tripped the breaker, and when I went back to how I had it wired before, it won't even start now at all, it just automatically trips the breaker.


Can anyone help shed some light on this for me? Is this a problem with the motor? Or am I just that big of a wiring illiterate that I better get an electrician?

 

[pattenp]

I have that same compressor. Mine is on a 30A circuit using #10 and if I recall that's what the install instructions recommended. When you say you used 3-wire, I assume you used a cord that has two hots with a ground? What size is the cord? Your two hots should be hooked to L1 and L2 on the pressure switch and obviously the ground goes to the switch box body.

 

[nehog]

...
I took it to my shop, which has 220 single phase wiring...

Where are you located that has 220 volts? If you are in the US, you should have 240 volts, and you need to confirm that. Next, with the compressor running, you need to measure the voltage at:

1. The breaker's feed (the main lugs in the sub-panel)
2. The breaker's output lugs
3. The compressor outlet
4. The compressor motor

Post those voltages (please use an accurate meter!) and I'm sure the problem will be obvious to someone here.

 

[Red Lion]

I have that same compressor. Mine is on a 30A circuit using #10 and if I recall that's what the install instructions recommended. When you say you used 3-wire, I assume you used a cord that has two hots with a ground? What size is the cord? Your two hots should be hooked to L1 and L2 on the pressure switch and obviously the ground goes to the switch box body.

Yep, 2 hots and a ground, it's 10 gauge. That's exactly how I have it too, the ground attached to the switch box body and the two hots to the L1 and L2.

Post those voltages (please use an accurate meter!) and I'm sure the problem will be obvious to someone here.

Will do, what's a good accurate meter to purchase?

 

[Falcon67]

Any decent meter from Sears will work they usually run around $40. If you are really bucks up get a Fluke (they sell those too). A $5 Harbor Freight meter will tell you what you need to know for this issue, really.

 

[wellpoison]

i wouldnt recomend something from harbor freight nor a fluke. but an extech or craftsman CAT 3 rated will cost you 30-50. grab one with a clamp to test amperage too.