Wiring for air compressor

Hello all. I am considering getting an air compressor for my home shop when I work on my classic cars and around the house. I can get a new one for a good price from a neighbor who bought a compressor and then sold his business. I'm looking at getting one that runs on household voltage, but I have a question:

1) I have a convenient plug in the garage, but I'm wondering if it's recommended that the compressor have its own circuit.
2) The service box is in the garage, and the compressor would be located there too.
3) Assuming I have an open spot on the service box, how would I run the wires to the box and to a new outlet? There's a box on the wall with a plate over it (I assume this is a junction box). Would I run the wires through that and into the box, to the new area on the service box? I guess my question is how does the new outlet get to the box without cutting open the wall. My guess would be that the wires would run through the junction box through the wall into the service box, and then the new outlet would be joined into one of the available knockouts on the junction box.

Any and all replies or pictorial information I could read up on and learn would be greatly appreciated. I wouldn't tackle this alone, but with someone with more electrical experience than I have of course. But, it is interesting to note how this is done. I want it to run safely, and without causing electrical problems in the house for other circuits.

Thanks.

 

Why not try it on an existing circuit. Depending on the size of the compressor pump, it may work just fine. For mine, I frequently tripped the standard 15-amp circuit, especially when it was cold in the garage. After adding a 30-amp circuit (slightly heavier gage wire with a dedicated 30-amp breaker), it always worked fine.

 

hello joe,
wheather you need a seperat circuit for the compresser will depend on what size it is. since you mentioned it is comeing from a shop this leads me to believe it will be of sufecent size to need its own circuit.

now as to running the new circuit into the panel. from the info in your post it sounds like the panel is set in the wall and sheet rock is in place. hopfully who ever installed this panel had the forsight to run a piece of conduit up threw the top plate for future use. if not then best way is to drill the top plate above the panel and fish the wire threw the hole and into the panel. the mention of a j-box above the panel makes me wounder if this box may go to the panel threw conduit worth checking out.

after you determin how you will get into the panel you need to run 12-2 with ground from the panel to location where you want the compresser and drill the top plate cut the sheetrock for the new box, fish wire threw hole in top plate to box cutout install old work box, install recep.
for 120 V
black to gold screw and white to silver and bare to the green, in panel connect the black to a 20 amp singel pole breaker white to the nutural bar and bare to the ground bar.
for 240V black and white to gold screws of 240V recep, bare to the green, in panel connect the black and white to a 20 amp 2 pole breaker, and bare to the ground bar.
these r generac instructions, you want to size the breaker to the compresser, it shuld tell you the max overcurrentt required for this unit on the name plate, if not simply sumit a post with voltage, and motor size and we can help you out.

 

Thanks gents. I will post more on the specifics of the unit if I get it from my neighbor, such as the amperage draw and other specs on the motor. I have to go see the unit and determine what it would need.

Yes, the garage has sheetrock in it already. I could probably ask my neighbor who would be helping me with the job, since his house was built by the same builders as mine.

Not sure if it is a commercial style unit or not. The guy selling it stated it was a back up unit for his brother's shop, but it was never used. It is assembled and ready to go, but it has never been used.

Thanks.....I guess when I get the unit I can see what draw it will have on a circuit. This would be a good start to determining a plan of action. I figure if I get a good deal on it, I would add the compressor to my arsenal of tools .

 

Ok everyone.

I finally bought this compressor. It's a brand new Craftsman oil free model, 4 hp, 18 gallon tank. It was never used and I picked it up with accessories for 75 bucks .

For a giggle, I plugged it in the outlet and had the garage flourescents on. Threw the breaker which is a 15A.

A couple of questions:

1) The owner's manual (which I got with the unit) states that it might work on a 15A breaker if there are no other draws on it, etc, etc. Makes sense. Not in my case would this work as the outlet has other things on the same line.
2) Why wouldn't this slot be a 20 Amp breaker? Would it be safe and as simple as to install a 20 Amp breaker in this slot and take out the 15A? I still have not investigated that junction box I believe leads to the service panel. If so, perhaps I can fish in a new line to it. The neighbor that sold me the compressor has a friend who is an electrician as well. I'd like to learn about this for my own edification though and perhaps for a future (or maybe this) electrical project.
3) How can I determine if I CAN EVEN ADD a new breaker. The box is marked with 16 slots on it, and the bottom right one is a 30 Amp breaker which is used for an air conditioner in the dining room. Does this just pop out (the blank and does one install a 20A in this portion of the box?

I'm thinking the hardest part of adding a new circuit is:

1) Making sure it can be done (adequate service to accomodate this load).
2) Getting the new wires fished to an available slot in the box.
3) Then just adding in the new box to the wall.

Want to do it safely, efficiently and properly and myself if possible. So bear with me if I ask a few novice questions here.

Thanks. I think I got a good deal on the compressor.

 

Would it be safe and as simple as to install a 20 Amp breaker in this slot and take out the 15A?

No.
Absolutely no.
Definitely no.
No way.
I don't think so Tim.

If you have a blank slot in your panel (i.e., a number embossed into the panel with no breaker next to it), then you can add a breaker. You need no other prerequisite.

I'd add a 20-amp breaker and then run 12/2 cable from it to an outlet dedicated for you new compressor. It's not very hard to do, but then again it's not very hard to get electrocuted doing it.

I think you have the basic steps down. You should get a book on home wiring so you know about other requirements such as stapling the cable, size of the box, protecting the cable, etc.

Ask more questions and we'll help.

 

Hi Joe,

Congrat's on the new compressor!! That is a beloved item on anyones wish list, and for $75, what a bargain! Really,, the stories I could tell looking for such a bargain. I live for bargains like that!

I won't even try to discuss your electrical concerns. I've been reading your thread and you sound like your in good hands with plently of talent on both sides.

I just wanted to add a tiny bit of insight about the location where you might mount this compressor. I have 2 close friends with compressors in their garage and I have been there working when they fire up. It's a bit(ch) noisy. It didn't bother me much at age 16 and a little more at age 30. But I have come to learn that the best place for a compressor is where it's sound is muffled. I know that it's not always possible and it's not a high priority item, but if you can, consider mounting the compressor in your basement. You will come to appreciate the muffled sound. Mine is in the basement closet and I am darn glad I hid it there. It sometimes comes on at night, but I never hear it down there! And draining the tank is no harder down there.
Also, resist the urge to mount it in your shop where you can see it and show it off. That is sure the heck where I would first want to put it. But, the bottom line is that it will be noisy as hell when you use it and it will occupy a large footprint on your floor. I can't tell you how many times I had to rearrange my shop to accomodate "THE NEXT TOOL". And trust me, there will always be 'ANOTHER TOOL'. Another minor item is this, if you spray paint in the same room with your compressor,(and we all spray paint in our garage, don't we) your compressor air intake will be sucking up combustible fumes and compressing them. Yuck.
But mostly, you don't want to have to loudly yell at your friend to 'HEY, HEY, HEEEYYYY, HAND ME MY BEER'.

But hey,, in another light, having a compressor is better than worrying about where to put it! Congrat's for the acquisition! Wait! Hey!! Isn't that tire a little low! Better check it out!!! Better yet, grab that impact gun, let's pop this puppy off and check for leaks.......

Mark

 

Good. That settles that concern. I didn't think so (which is why I asked the question in the first place).

Yes, #16 is blank. The one above it is occupied by the A/C. Therefore that one would be the one for the compressor. I will do as suggested and get some books on it. I've got some reading to do in this bad weather coming up the Northeast.

Will also need to investigate how it's to be added through the box and how to fish it through without breaking the wall.


Mark: I will have to get good hearing protection, as well as eye protection. This house is a high ranch and has no basement to mount the unit. In the good weather I can move the unit outside to work.

It surely needs a 20A breaker (as per even the printed instructions) which will be dedicated to it.
Thanks.

 

Guys I have a problem with what is being said, concerning this air compressor. I suggest that you check the name plate rating on that air compressor. Either you are miss reading or you have the wrong instructions for that air compressor.

I suspect that this air compressor requires 220 volts and 30 amp rated branch circuit.

A 4 horse power motor should require a full load current rating of 45 amps on 125 volt circuit. A 4 horse power motor should require a full load current rating of 23 amps on a 240 volt circuit.

Something is wrong on this subject. We need to research further and confirm the ratings of this equipment before it is energized.

Concerned

Wg

 

It's a household voltage model and the plate/sticker on it says:

15.0 Amps max (This is on a label with the model #)
8.2 SCFM at 40 PSI
6.2 SCFM at 90 PSI
125 PSI max.


It has a standard household plug. The instructions say that the compressor can be plugged into a 15A outlet if nothing else is on the circuit, blah, blah. With the garage lights off, the compressor would operate and not trip the breaker. (We tried this at my neighbor's house...the guy that sold me the compressor lives two doors down and has the same house as mine). It says changing the cord set is not necessary. What I noticed is that all of the appliances in the house (as noted with "APP" on the box label) are 20A and everything else is marked "LIGHT" is 15A. The dining room A/C is a 30A breaker and is above the vacant slot on the box. Does a 30A breaker take up TWO slots on the box perhaps? I can't really tell. Adajacent to #16 is a blank cover.

Most household compressors of this type are not actually making 4 hp in real terms. Oil free compressors spin at a faster revolution rate (and hence can burn out faster than their oil lubed counterparts). In reality, a compressor that you can plug in a "household" outlet really only makes 2hp in real terms. Naturally, the big stores such as Sears have used this as a marketing tool to market them as powerful units. In reality this is not the case. Ingersoll Rand rates their compressor different than a Campbell Hausfeld and a Sears would.

The instructions with it say if you cannot operate it on a 15 A circuit and the power is frequently interrupted, you should put it on a 20A circuit (which is what I'm going to wind up doing).

I'm hoping to learn how to do it myself, or at least have a handle in helping the individual in doing it.

Slot #16 as marked on the service box appears to be vacant, so I guess I can install the 20A breaker for this compressor here. (Someone mentioned if there is a vacancy, without a doubt another can be added). The one directly above it is a 30A for the dining room wall A/C. It was installed after the house was built in 1968.

Hope that clears it up, W.G. Any additional ideas are welcomed.

With all this weather in the Northeast, I should have a little time to get some books from the library and read up

 

I take it that you have an air compressor that has a 4 horse power rated pump but your drive motor is rated much less. Check to see if there is a lable on the motor itself. I suspect that the horse power rating of the motor itself is 1 horse power or less.

If this is the case then your breakers should protect you from overloading. If you plug it in and the breaker holds then you should be ok.

I suspect this air compressor is right at the border line of a miximum that a 15 amp circuit can hold. If you run the compressor with anything else running on that circuit your breaker will probably trip due to an overload.

If you experience this then run the 12/2 romex to the air compressor on a dedicated circuit from the panel. Install a 20 amp breaker and a single outlet rated for 20 amps not 15 amps at the compressor. Do not install a duplex receptacle on a garage wall without it being GFI protected.

Good Luck

Wg

 

Thanks WG. I think I've got the basics down pat.

It's going to be a 20A setup to prevent overload and to keep the compressor isolated from everything else.

There are other plugs in the garage which I use for various power tools or lights, so I want to leave those intact for that use. I plan on upgrading the lighting a little bit too.

For instance, on the ceiling is the garage door opener, which has a dual plug and only one is used.

I would like to install an additional double bulb hanging flourscent lamp there. This way it adds additional light to the garage and is "portable" in the sense of I can remove the plug if I need to use that outlet for something else in a pinch. I like flexibility with regard to these things.

As I posted before, the main issue is to hopefully not have to break the wall to add in that extra line. Right above the service box is a junction box which I'm hoping has room to fish a new line through the bottom of the box. The available circuit is #16, which is at the bottom of the box. Again, I have to read up on this more and get some more insight.

The main thing is safety and flexibility. I don't trip any circuits now, so I don't want to by adding this piece of equipment.

I think I will reserve some books on home electricity from the public library right now .

Thanks again. If anyone has additional information, I'd be glad to hear it. I will post my results (might be in the spring though!) when I do the job.

 

WG and crew:

The cop neighbor/friend of mine who sold me this thing has a friend that is an electrician for the City of New York.

I called him over and he will install all of the needed outlets (I want two) with the proper 20 Amp breaker and labor, etc for $100

Money well spent to do it right the first time. He will come in 2 weeks.

I plan on upgrading the lighting in the garage...something I think I can tackle on my own as there is already one bulb flourscent fixtures there now...I want to put double bulb ones there now.

Thanks for all the comments and information.

Yea, I work slow. . Too many other projects around the house!

 

You can install an old work box right under the panel, using the cutout as access to install the connector and feed the wire. You are right about the horsepower,,, I totally ignore the thing on the box that says HP,,, its marketing garbage and look at the plug that comes on the end or the motor draw. I think is a disgrace to let them rate stuff locked rotor,, what a joke. Also try to get it on the opposite leg as the lighting,, you might have to swap a breaker or 2 around.

 

Something else to consider with these types of compressors,, and this applies to piston type and rotary might be a bit more efficient,, not sure how much but it isnt a great factor,,, but, figure it at 4 CFM per HP and use the figure of 12 amps per hp on 120v and 6 at 240 for this calculation. You will need to make 4 times the air that will make to run a DA sander continious. It will run a air ratchet for a burp and is good for blowing dust off or filling a tire. Dont get your shorts all in a bunge when you try to run tools from it,,, there is nothing wrong with the unit,,, it is VERY small. It will make 4 cfm, 6 or so at best at low pressures,, which is considered 90 or so. When you buy an air tool, the rating is an AVG CFM rating this is only a 1/3 or so of the air it requires. That rating is an industrial factor for rating the use of multiple tools in factory, NOT an actual use rating. Its a great thing for 75$ though and I probably would have bought it just for the heck of it,,, it will give some air and work great for roofing nailer and such.

 

I am going to add another couple cents worth here while we are on compressors as there are a lot of them out there in small garages. Air is NOT an efficient way to power tools. It is used for all kinds of other reasons. Compactness of tools, durability in dusty conditions, user saftey, no cords etc. We use electric grinding in welding shop as the input power is 1/5th of what it would be for air to spin the same tool. Sometimes this is not a factor where the user is buying power wholesale or the savings add way up and the cost to operate isnt a factor in the job. A mechanics shop is a good example,, the tools need to be compact, durable and the use is intermitant. An electric impact is a good example,, its use is short duration, the tool isnt as durable as air and is not as compact and the labor rates are high so air makes sense.

 

Good point and quite true.

The main use is for automotive work around my house. I own six cars personally and probably service 15 more for relatives and friends as a hobby/requirement.

So, air tools are a boon for me. This all started with me getting that compressor for next to nothing from a neighbor, essentially brand new .

Thanks for the additional input.

One has to remember another thing that you alluded to: You still have the air hose in your way !

 

Joe_F, I sure am glad to see I'm not the only one who still has things on his 'To Do' list from 2 years ago.

 

Lol. Such happens when you have two houses, six cars (plus 15 others of friends and relatives to maintain), as well as two lawns, and countless other things to do.

Oh yea, there's work and sleep too. LOL. I try to do everything myself where feasible and learn from what I do, and read and research it all.

Actually, the compressor was an "impulse" item. My neighbor simply came up to me and said, "Can you use a compressor?"

After some thought I said to myself, "Not a bad idea". Being he's a neighbor I wanted to be fair. He originally wanted 125 bucks for the thing, but I asked him if 75 was reasonable as I could buy one like it in Sears for close to his asking price.

The kicker was that this one was brand new and the wheels had never been installed. It came with a hose, the owner's book and a blowgun, so for 75 bucks I couldn't go wrong .

I have a list of my projects that I just peck off as I get them done .

 

The outlets are in. Two of 'em, on a 20A breaker with 12 gauge wire installed, 80 bucks. Done in one hour by the electrician friend of my neighbor that sold it to me 2 years ago .

I learned something by watching him do it and I want to say thanks for everyone's help on it.