Hello:

I have a Sears Craftsman 6hp 150 psi 33 gallon compressor. Electrical measurements are 120v/15amps - basically meaning it could run on normal household current. However, when I start it up, after about 3 seconds, it shuts off. I tried using the dedicated outlets in my apartment, meaning the air conditioner & fridge outlets, all rated at 20 amps, and it still trips the breaker. I'm guessing that I need more power so I was going to install another breaker with a higher amp rating. Is it possible to do this without ripping into the walls etc - because it is an apartment after all. I was guessing on using some tubing or runners that I could put the wiring into, however, my dilemma is if I could even install the new breaker (running the wiring into the breakers wire etc etc). What amp rating is recommended? I was guessing 40 amps or higher. Also, are there any alternatives I could use as opposed to installing a new breaker? Thank you & have a good day.

Before you install a over-sized breaker that will keep your 15 amp compressor running, you may want to look into why it trips a breaker that's suited for that operating amperage. It's possible that something is wrong with the compressor that is causing excessive draw. I think I'd contact an authorized Sears repair facility to get your compressor tested. And look into getting an adequate ABC extinguisher to keep handy. Safety is paramount.

Something is wrong, you state a 6 HP 120 volt motor. That should have a nameplate amps of close to 55-60 amps. Or 28 amps at 240 volts.

Confirm the HP size of the motor.

Also, doing your own electrical work in a multi-family dwelling may not be allowed in your state.

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Originally Posted by tkrussell

Something is wrong, you state a 6 HP 120 volt motor. That should have a nameplate amps of close to 55-60 amps. or 28 amps at 240 volts.

Confirm the HP size of the motor.

Also, doing your own electrical work in a multi-family dwelling may not be allowed in your state.

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That's what I figured. That's why I wanted to start looking into some portable forms of power. However, before I do that I'm going to have a Sears center check it out. As far as the nameplate - it states: 120v/60hz/1ph/15a. Strange isn't it? Thank you & have a good day. I'll keep you posted.

I'm familiar with this compressor, my neighbor has one, and it is 120v/15amp. I also checked my Sears catalog and they only have one 33 gal model,a portable unit like my neighbor's, so I'm sure this is the one you're referring to. Sears rates their motors based on peak horsepower to make it sound better, and just recently also started listing the running HP. This motor is rated at 6HP PEAK and only 2 HP RUNNING. My neighbor has it on a 20amp breaker on a standard outlet with no problem. I would check the on/off switch (a mechanical/pressure relief switch), the motor startup capacitors, and the windings/ brushes in the motor. Since it runs for a few seconds it sounds like something heats up then shorts out or then draws too much current causing the trip...

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Originally Posted by shader

I'm familiar with this compressor, my neighbor has one, and it is 120v/15amp. I also checked my Sears catalog and they only have one 33 gal model, like my neighbor's, so I'm sure this is the one you're referring to. Sears rates their motors based on peak horsepower to make it sound better, then in fine print lists the running HP. This motor is rated at 6HP PEAK and only 2 HP RUNNING. My neighbor has it on a 20amp breaker with no problem. I would check the on/off switch (a mechanial/pressure relief switch), the motor startup capacitors, and the windings/ brushes in the motor. Since it runs for a few seconds it sounds like something heats up then shorts out or then draws too much current causing the trip.....

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Wow - now that's a surprise!! When does it ever hit the 6hp range then hehehehehe!!
Hmmmm... that's interesting - good your're very familiar with this model. How do I tell if it's anything wrong though? Should I look for discoloration, get an electrical testing device, bends, cracks, etc. I'll pull it apart today and check it out. The windings & brushes I may have to get familiar with but I'm sure I'll find them. I'll keep you posted as to what happens. Thank you & have a good day.

It probably only hits 6HP at start up which is for a very short period of time-I'll admit I'm not that familiar with how that's determined. I have an Ingersall Rand light industrial compressor rated at 11Hp peak, 5 HP running so the same type of rating used. As TKRussell stated, a true 5 or 6HP motor needs some serious power; in my case 220V/28 amps. Your's is made for consumer use so it is made to be used on a standard outlet. As for checking things out start with a visual inspection. The switch and capacitors need special equiment to test. The motor windings and brushes are in the motor housing. The windings could be shorting, again needing eqpt. To test it. The brushes are somewhat easy to replace, but unless you're familiar with motor repair it is best to let Sears service look at the whole unit. One last thought, is it possible the compressor itself, (the unit that compresses the air), binds up and puts a drag on the motor, causing excessive current draw and trips the breaker?

You can probably find out a lot by separating the motor from the compressor...
Try to see how freely the motor turns by hand,
Try to see how the compressor turns by hand...

I think the motor alone probably runs freely, and maybe get a little hot, but shouldn't trip breaker...

I am almost willing to bet that the compressor is binding and putting too much load on the motor...

Poor lubrication is what I would look for ( A shaft heats up and starts binding )
Bad bearings -- mechanical things??

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Originally Posted by shader

It probably only hits 6HP at start up which is for a very short period of time-I'll admit I'm not that familiar with how that's determined. I have an Ingersall Rand light industrial compressor rated at 11Hp peak, 5 HP running so the same type of rating used. As TKRussell stated, a true 5 or 6HP motor needs some serious power; in my case 220V/28 amps. Your's is made for consumer use so it is made to be used on a standard outlet. As for checking things out start with a visual inspection. The switch and capacitors need special equiment to test. The motor windings and brushes are in the motor housing. The windings could be shorting, again needing eqpt. to test it. The brushes are somewhat easy to replace, but unless you're familiar with motor repair it is best to let Sears service look at the whole unit. One last thought, is it possible the compressor itself, (the unit that compresses the air), binds up and puts a drag on the motor, causing excessive current draw and trips the breaker?

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I'm not entirely sure - but that sounds like it could be a possible problem because the wiring in my apartment is heavy copper wiring so... If it needs equipment to test, for convenience sake, I'm going to take it into a Sears service center. I'll keep you posted and let you know what they say. Thank you & have a good day.

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Originally Posted by biggsie

You can probably find out a lot by seperating the motor from the compressor...
Try to see how freely the motor turns by hand,
try to see how the compressor turns by hand...

I think the motor alone probably runs freely, and maybe get a little hot, but shouldn't trip breaker...

I am almost willing to bet that the compressor is binding and putting too much load on the motor...

Poor lubrication is what I would look for ( A shaft heats up and starts binding )
Bad bearings -- mechanical things???

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Hello. Thank you for your response. I'll look into these matters as well. I'll keep you posted and let you know what's going on. Thank you & have a good day.

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Originally Posted by CaptainRich

Before you install a over-sized breaker that will keep your 15 amp compressor running, you may want to look into why it trips a breaker that's suited for that operating amperage. It's possible that something is wrong with the compressor that is causing excessive draw. I think I'd contact an authorized Sears repair facility to get your compressor tested. And look into getting an adequate ABC extinguisher to keep handy. Safety is paramount.

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Hello. I don't think I responded to your question right the first time to where you'd see my response in an email or something - but I got used to how this website works for responding. Here's my response:

Thank you. I think I will look into that. It's an issue I don't understand myself - because if they say it's rated at that amperage, then it should operate. I'll take it into a Sears center and see what's going on. I'll keep you posted. Thank you & have a good day.

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Originally Posted by biggsie

You can probably find out a lot by seperating the motor from the compressor...
Try to see how freely the motor turns by hand,
try to see how the compressor turns by hand...

I think the motor alone probably runs freely, and maybe get a little hot, but shouldn't trip breaker...

I am almost willing to bet that the compressor is binding and putting too much load on the motor...

Poor lubrication is what I would look for ( A shaft heats up and starts binding )
Bad bearings -- mechanical things???

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Hey Biggsie -

Quick question. I forgot to mention that the compressor is oil-less. Could I still lightly lubricate the shaft and/or what appears to be a large piston? Or is it inadvisable to do that because of a difference in the way it's built? Thank you & have a good day.

The first thing to do before you go into the motor is to make sure that the pressure switch is unloading, if not your motor is trying to start under what ever pressure is in the tank.
I do know that this is a problem sometimes and is about the easiest thing to fix.

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Originally Posted by letmetellu

The first thing to do before you go into the motor is to make sure that the pressure switch is unloading, if not your motor is trying to start under what ever pressure is in the tank.
I do know that this is a problem sometimes and is about the easiest thing to fix.

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Hello. Thanks for the advice. I opened up the pressure relief switch housing. Inside are 4connecting wires with 2 wires at the bottom - in total 6. The wires attached to the bottom are green, the wires attached to the terminals labeled 3 L2 & T2 4 are white, and the wires attached to the terminals labeled 1 L1 & T1 2 are black. I looked at the connection diagram under the cap but that doesn't say anything. It does show which wires to connect as far as the line wire (to the plug) and the motor wire, but it doesn't give the color pattern. Anything I should particularly look for or do (switch the order of white & black wires etc.)? Thank you & have a good day.

letmetellu had a good point on the unloader. Though I mentioned it in one of my posts, that's about all I did. THere shoud be a small copper line from the compressor/tank to the switch. If it's an external type there should be what looks like a plunger setup at the switch. You can move this by hand and make sure it moves freely. Clean if dirty. This releases pressure from the head/line when the unit shuts off, so when it restarts the motor won't start against any pressure. Some of the newer switches have the relief inside the switch mechanism and I'm not sure how to test that. THe "L" desigations are for the line/power supply and the "T" for the motor, green is ground. Don't move the connections around, that is not the problem.

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Originally Posted by shader

letmetellu had a good point on the unloader. Though I mentioned it in one of my posts, that's about all I did. THere shoud be a small copper line from the compressor/tank to the switch. If it's an external type there should be what looks like a plunger setup at the switch. You can move this by hand and make sure it moves freely. Clean if dirty. This releases pressure from the head/line when the unit shuts off, so when it restarts the motor won't start against any pressure. Some of the newer switches have the relief inside the switch mechanism and I'm not sure how to test that. THe "L" desigations are for the line/power supply and the "T" for the motor, green is ground. Don't move the connections around, that is not the problem.

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Hello Shader:

Thank you - whew!! I'm glad I didn't remove the wires or anything! I believe I have the external type and will look into that. I'll keep you posted. Thank you & have a good day.

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Originally Posted by hj3

Hello Shader:

Thank you - whew!!! I'm glad I didn't remove the wires or anything! I believe I have the external type and will look into that. I'll keep you posted. Thank you & have a good day.

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Hello all:

I received very helpful comments from everybody. The problem was with the unloader - or so I think. What I did was I released the line that connects to the unloader, released the plunger looking attachment. I inspected the line & plunger making sure it was all clean & had no interference. I blew inside of the line as well. I reinserted them back on and started back up the compressor and it worked!! Thanks everybody for your help.

Hopefully that was the only problem and the compressor will keep working. Keep the unloader clean-the external ones tend to get dirty and stick, especially under dusty operating conditions. Now you can do some spray painting in your apartment :eek:

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Originally Posted by shader

Hopefully that was the only problem and the compressor will keep working. Keep the unloader clean-the external ones tend to get dirty and stick, especially under dusty operating conditions. Now you can do some spray painting in your apartment :eek:

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Hehehe... oh yeah! I was very worried because the cost of a new motor - well for a bit more I could get a new compressor but then the issue of what to do with the leftover tank arises. So I'm pretty glad I didn't have to go that far!! Thank you very much!!