# Craftsman air compressor blowing breaker



## Yoyizit (Jul 11, 2008)

Plug the thing into a long extension cord, more or less of the AWG size specified in your saw's manual. See if this improves your odds as to tripping the breaker.

I guess if there is a high resistance anywhere upstream of the motor, it will demand more current. You could check the voltage drop in motor wiring from the motor input to the compressor plug while it's running, and calc. the expected resistance from the wire size. Closed contacts at rated current should read less than 100 mV across them.


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## Gigs (Oct 26, 2008)

> 5.5 max H.P


This number is pretty much just made up.


> What else can I do other than running another line? If I do this I'm gonna run a 50 amp breaker.


Bad idea. If it's tripping a dedicated 20 amp breaker instantly, it's basically a short circuit. A 50 amp breaker will likely trip just as fast.


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## Yoyizit (Jul 11, 2008)

*this doesn't sit right*



Frankenberry said:


> blew once in awhile.
> on startup or later?
> 
> The compressor now works better but it still blows 50 percent of the time.
> ...


Maybe the tripping with the first breaker was a fluke, and both 20A breakers are good, but you might need a different trip curve (if it takes minutes to trip the breaker).

Your motor may have developed shorts that are partially shorting the windings that weren't there when you ran the original setup.

This HP at 120v is 34A; if the motor draws temp. high current lasting seconds it might squeak by with a 15A breaker. Home welding machines drawing very high current depend on the welding process lasting only a minute or so.


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## Frankenberry (Feb 19, 2009)

Yoyizit.

Sometimes it blows right away, sometimes it blows after a minute, sometimes it blows after several cycles.


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## Yoyizit (Jul 11, 2008)

Frankenberry said:


> Yoyizit.
> 
> Sometimes it blows right away, sometimes it blows after a minute, sometimes it blows after several cycles.


I'd say the compressor is intermittently failing, but you might want to measure current draw with a clamp-on meter, but this will not show high current spikes. For that you need an oscilloscope and a shunt.

Also measure motor ohms, disconnect the meter and turn the shaft and measure again. Average a few readings. Don't turn the shaft with the ohmmeter connected.

As a coarse troubleshooting aid only, you might wire it to breakers considerably larger than 15A. 
If the compressor intermittently shorts due to vibration it should probably blow these larger breakers also.

This is about as hard as it gets. The randomness bespeaks of great evil within this device!


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## Gary_602z (Nov 15, 2008)

Just thinking out loud here. But is there a one way check valve on the compressor that keeps the tank pressure from back feeding back into the compressor? If so and it was allowing air in the tank back it could make the compressor work harder or deadhead on startup.

Gary


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## 220/221 (Oct 9, 2007)

Can he just install a 30 amp breaker according to article 440 ??

They are telling me at Mike Holts) that I can install *#12's* on a *40 amp* breaker to a motor load (AC). Is this compresor viewed differently from an AC compressor or other motors in 440?

I don't have a code book with me. Maybe it's reserved for motors with certain protection built in.


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## Frankenberry (Feb 19, 2009)

Gary,
It does have a check valve and I made sure it was working correctly when I replaced the pressure switch last night.


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## micromind (Mar 9, 2008)

The reason the breaker trips occasionally is because the starting current of the motor is very close to the magnetic tripping current of the breaker. Basically, the breaker is seeing the motor starting current as a fault. 

These compressors are notorious for extremely high starting current. One solution, if your panel is Square D QO (not homeline) is to get a high-magnetic 20 amp breaker. The model# is QO120HM. 

The 5.5HP rating is not the actual running HP, it's the maximum HP the motor will produce before it stalls. It would produce 5.5HP for less than 2 minutes before it burns up. The actual running HP is more like 2 HP or so. Look on the motor nameplate, I bet is says for amps (FLA) something around 20. 

If the compressor is hard-wired (not cord-and-plug connected), according to article 430 (motors) in the code, the maximum breaker size is 250% of the full-load current. Usually, we use a table in the codebook that gives amps vs. HP, but I bet this motor doesn't list a HP on the nameplate. It very likely says HP...SPL. The minimum wire size is 125% of the full-load current. 

Therefore, you could use a larger breaker than the wire is normally rated for, but in no case can you use a larger breaker than the receptacle is rated for. So the compressor must be hard-wired, and it must be the only thing on the circuit. 

Rob


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## Yoyizit (Jul 11, 2008)

Does the compressor start under full load (i.e., high inrush)?


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## Frankenberry (Feb 19, 2009)

I'm interested in what micromind said. Does this mean if I cut The plug off, take out the outlet and wire it directly I can use a 30 amp breaker with 12 ga wire? This will be a dedicated circuit.


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## wirenut1110 (Apr 26, 2008)

In your owner's manual it says a 15 amp circuit but it can be changed to a 20 if needed. There's something wrong, and I would try to assess that vs. up sizing the breaker. Centrifugal switch perhaps?


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## Yoyizit (Jul 11, 2008)

wirenut1110 said:


> There's something wrong, and I would try to assess that vs. up sizing the breaker.


Amen.


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## Frankenberry (Feb 19, 2009)

Well, I did cut off the plug and wired it directly in the box. I left the 20 amp breaker in. I have a job tomorrow that I will use it with, so I'll see how it's working.


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## Yoyizit (Jul 11, 2008)

Frankenberry said:


> Well, I did cut off the plug and wired it directly in the box. I left the 20 amp breaker in. I have a job tomorrow that I will use it with, so I'll see how it's working.


If this works then the contact impedance of the plug/socket was to blame? 
Unlikely, but who knows. . .?


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## micromind (Mar 9, 2008)

If the compressor is permanently wired (no cord-and-plug), and it's the only thing on the circuit, then it's code compliant to use a larger than 20 amp breaker with #12 wire. How much larger depends on the motor HP or FLA (full load amps). 

If you need the code references, just ask, and I'll post them. It's pretty long though. 

Rob


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## Frankenberry (Feb 19, 2009)

Well it ran fine today. At least a dozen on/off cycles. I left in the 20 amp breaker. I don't know if it was the new breaker, the new contact switch in the compressor, or the elimination of the plug, but I hope that's the end of the problem. Thanks for everyones input and advice.


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## ceyko (Sep 5, 2009)

Frankenberry said:


> Well it ran fine today. At least a dozen on/off cycles. I left in the 20 amp breaker. I don't know if it was the new breaker, the new contact switch in the compressor, or the elimination of the plug, but I hope that's the end of the problem. Thanks for everyones input and advice.


So I have a "5.5 HP" 30 Gallon Craftsman doing the same thing. Replaced the check valve with no luck and was curious if your problem was fixed or not.

Mine starts from empty with 0 problems. It's when under pressure that it gives me a hassle.

Take care,


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## kbsparky (Sep 11, 2008)

Please post all the nameplate information from your compressor motor, and provide details on how it is wired:

HP
FLA (full load Amps)
LRA (Locked Rotor Amps)
Volts
SF
etc

Is it connected to a dedicated outlet, or direct wired? Wire size, and breaker size? Brand name and type of breaker panel? Distance from panel to compressor? etc


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## ceyko (Sep 5, 2009)

kbsparky said:


> HP
> FLA (full load Amps)
> LRA (Locked Rotor Amps)
> Volts
> ...


Greetings,
I'd like nothing more to answer those questions, but I looked and am unable to find that information right now. I'll look again and maybe tearing her apart tomorrow.

However, I'll answer what I can...
The instruction manual says to install a 15A/110V circuit. I installed a 20A, 110V, GFCI (garage, my code says it has to be) circuit just for it. So, it is not hardwired, but it is a dedicated circuit. The romex/wire I bought was 12/3. The run is all of about 2' long since I put it right next to my breaker panel box where the compressor sits. The compressor cord is around 5' long. I was very careful during installion of the breaker/circuit to make sure connections were good...etc. Also, to note the breaker pops, not the GFCI. Dunno if that helps.

People are saying, "just throw in a breaker/GFCI plus and be done with it." I just don't think that is a smart move considering 20A should be overkill.


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## AndrewF (Dec 29, 2008)

If your unit has a starting capacitor, I would replace it. It has likely gone bad and is not able to provide enough current for the LRA of the unit.

If the unit is able to run on 220, I would convert it to 220. It cuts your current (amp) draw in half.

Also, you said you ran 12/2 in conduit under ground. Did you get UF 12/2 or are you using regular romex? Romex is not rated for underground/wet conditions.

You need to run either UF or individual THWN runs for the underground portion.


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## J. V. (Jun 1, 2007)

*A five Hp motor draws 28 amps @230 volt.* NEC Table 430-152 allows a maximum of 250% to size your single phase motor with a inverse time breaker. This is a common breaker like you have in your panel. Here are the instructions.

5Hp Single Phase Motor

28 amps x 2.50 = 70 amps. This is the maximum size breaker allowed to be used on your motor. This is size breaker I would use. Now, the wire. The motor pulls 28 amps full load. 28 is very close to 30 and #10 wire is good for 30 amps. So I woulds use #10 wire. #12 may work but it's to small in my opinion. 
Install #10 wire and install a 70 amp breaker. No more tripping and code compliant.


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## ceyko (Sep 5, 2009)

kbsparky said:


> Please post all the nameplate information from your compressor motor, and provide details on how it is wired:
> 
> HP
> FLA (full load Amps)
> ...


Actually, I found a lot of what you're looking for...but some of what you listed is not on there. I'll line it out as it is on the label...

Motor - GE Model 5KCR49TN2312CX
HP HZ60
V120 PH1
RPM 3450 CODE K
A15.0 SF1.0
SFA-- FR56Z
AMB40 C

That is about it on the motor.


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## micromind (Mar 9, 2008)

There are two possibilities here, electrical or mechanical. 

First, mechanical. Every air compressor has to have some type of unloader. The purpose of the unloader is to relieve pressure at the pump when it shuts off. Very few cheap factory compressors (yes, your is indeed a cheap factory compressor, more on that later) can start against pressure. If the unloader has failed, it'll start OK when there's no pressure in the tank, otherwise, no. 

There are two types of unloaders commonly used on these compressors. One is an unloader valve. This is a combination check valve and unloader valve. One end is screwed in to the tank, and the other goes to the pump. This valve has a small hole in the side, when the pump shuts off, the air in the line is released through this hole. 

The other type, more common, is a valve at the pressure switch. This has a small (1/4") tube attached, and when the pressure switch shuts off, it opens the valve, thus releasing the pressure in the line. 

Usually, you can hear the air hiss at these valves when the compressor shuts off. If the unloader has failed, nothing electrical is going to fix the problem. It simply won't start if it's not unloaded. 

Now, for electrical. This motor is actually about 1-1/2HP. I know, the label says 5.5HP, there's absolutely no possible way that this motor will EVER produce 5.5HP. That being said, a 15 amp motor will not operate on a 15 amp breaker. I know, the book says use a 15 amp circuit, obviously, the book was written by an idiot. A 15 amp motor MIGHT operate on a 20 amp circuit. If it does, it's pushing the breaker to its limits. 

This motor draws around 100 amps during starting. That's above the magnetic trip setting for nearly all 15 amp breakers, and very close to it for a 20. Worse, it's 3450 RPM. A 3450 RPM motor has substantially less starting torque than a similar 1725 RPM one. This magnifies an already questionable situation. 

A 3450 RPM motor is less costly to manufacture than a 1725 is, hence the cheapness factor. As a side note, any air compressor that has a 3450 RPM motor was built primarily for low cost. 

If this were mine, I'd get rid of the GFI, chop the plug off of the cord, get a metal blank plate with a knockout in it, and using a suitable cordgrip, hardwire it. Then I'd replace the breaker with a 30 or even a 40. This would be a code compliant installation, even with #12 wire. 

Also, provided the unloader works, it'll start every time.

Rob

P.S. A few years ago, there was a good-sized lawsuit against several compressor manufacturers concerning the HP ratings of their products. It seem that the manufacturers were pretty much picking HP ratings randomly, and marketing their products as superior to others. I don't know the outcome, but I see more labels like 5.5HP, then in fine print (1.5 running HP).


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## ceyko (Sep 5, 2009)

Hey micromind,
I replaced the "check valve" and I THINK I can hear the 'hiss' when it is done. I'll be running outside to check that for sure after this post, but I'm nearly certain that sound is present.

I don't want to pretend to understand compressors, so I'll ask a straight forward question - will a 30A circuit, hardwired directly to the compressor be sufficient - assuming it is an electrical issue? I have no problems doing this and keeping my GFCI circuit for other things.

I'm just hesitant to do more then 30A.

Thanks for the big rundown too. I was under no illusions that this compressor was high end, I was just looking for a big tank (to me, compared to 6 gallon tanks I have), some okay CFM and reliability. I got 2 of 3, which reliability is the big one for me.  If it seems 30A is enough, I'll try it and post up if it works. One thing I noticed on all these threads on the internet...no resolution.


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## kbsparky (Sep 11, 2008)

ceyko said:


> Actually, I found a lot of what you're looking for...but some of what you listed is not on there. I'll line it out as it is on the label...
> 
> Motor - GE Model 5KCR49TN2312CX
> HP HZ60
> ...


Notice that the HP rating is left blank. That is because it is _not_ a 5½ HP motor. According to the chart in section 430.248 of the NEC, it is more likely a *one *horsepower motor. Actually, the one HP motor is stipulated to require 16 Amps. So you might have a bit less than one HP available. But for the purpose of this discussion, let's assume that this motor is an energy-efficient type and only requires 15 Amps.

That is full-load current. Starting current is approx. 6 times the running current. This means you need 90 Amps to start the dang thing. Table 430.251(A) of the _Code_ bears this out, and shows maximum 96 Amps locked rotor current for a 1HP motor. Locked Rotor Amps and starting current are similar values.

Now for the wiring. IF you install this motor on an individual circuit, you can upsize the breaker to 250% of the full load amps of the motor. This translates to 15x2½=37½ Amps. Since there is no such thing as a 37½ Amp breaker, you are allowed to use the next standard size breaker. This means a 40 Amp breaker would be acceptable. 

Section 430.22 of the _Code_ mandates that the wire size for this motor be capable of carrying 125% of the full load current. 15x1.25=18.75 Amps. Table 310.16 shows a #14 wire being capable of handling 20 Amps. The limitations of section 240.4(D) showing 15 Amps max. for a #14 wire do not apply here, as we are dealing with section 240.4(G). 

While the _Code_ allows a #14 wire protected by a 40 Amp breaker in this instance, I personally would install a #12 wire, as that #14 is really max'd out. :whistling2:


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## ceyko (Sep 5, 2009)

Lol, wow. 40A for a 15A motor. I'm glad I posted here and received yalls help. Initially I was going to do a 30A, but glad I did not waste the time ordering the GFCI circuit. I supposed it would not need to be any sort of GFCI for a direct connect to the compressor, so 40A - non-GFCI hardwired it is I guess. Wow, I had no idea.


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## micromind (Mar 9, 2008)

kb is right on the dot. 

If the compressor doesn't have a small pressure line at the pressure switch, then it most likely has an unloader valve. This can be confirmed by the hiss when it shuts off. 

If you can turn the pump by hand, it should turn easily when unloaded. If its still pressurized, it'll turn easily, then hard. 

Rob


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## kbsparky (Sep 11, 2008)

If you chose to use a cord-and-plug connection on this, I suppose that since it's in a garage, you would be required to have GFCI protection. Either a GFCI breaker or a GFCI receptacle. As you previously noted, it was the breaker and not the GFCI that was tripping out.

Direct-wired would not require this, however. :no:

Since it is adjacent to the panel, no further disconnect would be required, either.


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## ceyko (Sep 5, 2009)

Thanks all for the help so far. Just got back from Lowes with a 30A and 40A breaker (just going to test for my own knowledge) and other misc parts to hard wire the compress to the breaker box. Hoping this resolves the issue, but either way - thank you.


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## kbsparky (Sep 11, 2008)

I suppose that those breakers are double-pole? Be sure to use only one pole, since you are dealing with a 120 Volt load. White wire to the neutral bar!

Quickest way to burn out that motor is to hook it up to 240.... :furious:


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## ceyko (Sep 5, 2009)

kbsparky said:


> I suppose that those breakers are double-pole? Be sure to use only one pole, since you are dealing with a 120 Volt load. White wire to the neutral bar!
> 
> Quickest way to burn out that motor is to hook it up to 240.... :furious:



30 Amp is single pole, but the 40A was double. Was googling to figure that out. May need to shop HD instead for single pole 40A if needed.


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## ceyko (Sep 5, 2009)

I hooked up a 30A breaker and it MAY have helped, but I'm not sure. Problem was the connectors I bought were for 12ga wire, but they would not crimp onto the solid core wire in any manner considered good.

Also, the connectors that slid onto the compressor were loose. Any recommendations for good connectors for this little job or is there better wire to use?

Anyway, long story short I THINK it helped - but with my shoddy connections coming loose it would fail. I felt the wire get hotter then I think is normal and eventually the thermal protection on the motor kicked in. However, that was while I was testing. Until I get good all around connections I can't be sure. 

Do they make a cable that is a standard 110 cable on one end and a pigtail for the breaker box on the other? Then I could just leave the plug in place that is there now. Lowes did not have it, Unless I were to cut an extension cord. Is cable that is stranded okay for a breaker box?

Take care,


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## Gigs (Oct 26, 2008)

ceyko said:


> Do they make a cable that is a standard 110 cable on one end and a pigtail for the breaker box on the other? Then I could just leave the plug in place that is there now. Lowes did not have it, Unless I were to cut an extension cord. Is cable that is stranded okay for a breaker box?


No, don't do that. Just run a little piece of romex out of the breaker box to a metal surface mount junction box. If you absolutely must, you can splice a stranded whip to the romex in the junction box... make sure you clamp it good in there.

The code sticklers might have some other solution, but what I just told you would be good enough. An extension cord directly into your breaker box is a bad idea for a lot of reasons.


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## ceyko (Sep 5, 2009)

Gigs said:


> No, don't do that. Just run a little piece of romex out of the breaker box to a metal surface mount junction box. If you absolutely must, you can splice a stranded whip to the romex in the junction box... make sure you clamp it good in there.
> 
> The code sticklers might have some other solution, but what I just told you would be good enough. An extension cord directly into your breaker box is a bad idea for a lot of reasons.


Thanks for the heads up, I should've thought about a junction box. I know what they are, sort of - even if I never used one.

Extension cord straight to the box did seem like a bad idea, but ...easy.


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## Thurman (Feb 9, 2009)

As a person who has worked on air compressors in size from 1 1/2 HP-360 HP, and from 2.2 CFM-1600 CFM, I may know something about them. "micromind's" post #25 was very good regarding the unloader. Yes, all air compressors have to "unload" when they reach their max operating pressure, whether they shut down or stay running (as big one's do). IF you're compressor does not unload properly, then it will be hard for the motor to start it back up and therefore draw a large electrical load (current) and probably trip a breaker. As has been stated here before: Once a breaker trips, it's life has been shortened greatly. Most manufacturers do recommend changing a breaker that has only tripped once. You should be able to hear your compressor "unload" about one second after the electric motor shuts off. This should be a distinct, quick, "high pressure air escaping and decreasing" sound, lasting about a second. If you're not hearing this, then you have an unloader problem, which is creating an electrical problem. So many things to check, Good Luck, David


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## spark plug (May 5, 2009)

*attempting to find reason for breaker trip*

KB Sparky and Micromind just about said it ALL! About taking into consideration the FLA, LRA and the probability of the Staring Capacitor gone bad. But in my humble opinion the kicker here is the Amperage. BTW. this proves that the nameplate rating of 5.5 Amps is more than an exaggeration. Because that would bring the Wattage of this motor to 4.103 KW. The current draw @ 120v. would work out to 34.19 Amps. First off, no 120v. Receptacle is rated @ this Amperage. More proof is in the fact that there are no FLA and LRA ratings given. The TRUE output is (probably) closer to 2-2.5 HP! (eliminate confusion:yes::no through Education!! :drinkon't Drink and Drive, Ever!!!


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## ceyko (Sep 5, 2009)

For what it's worth, a local to DFW friend helped me out. I took my compressor over to him and it turns out a plastic part was busted, that stopped the mechanisms on the start capacitor to be tight against the motor. Once secured, it starts no problem. I completely did not notice this unti it was pointed out to me.


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