Wiring Ideas for new (to me) compressor

[Greg Scull]

This week I picked up a new (to me) compressor. Its a much larger unit than my old one I inherited from a friend when working auto body. Old one served me well for about 10 years but wanted more capacity. My ad in CL for "wanted large tank compressor working or not" yielded this beast. Its a 2HP motor 12amp with a craftsman pump mounted on it. Not sure of the other specs and either was the seller. I had my heart set on a 5HP but my wallet wasn't with me on that .

The guy I got it from said it was working well when last used. Translation: you are going to have a heck of a time to get it working again .

Catch is its my first 220 machine and now I need to add a new outlet for it.

I was thinking of adding a sub panel which I have read many have done here but am hesitant due to the "virtual closet" space requirement. Also there is plenty of room for more in my main panel which is pretty close, on the other side of the wall on the outside is my main (square D) panel which has 7 remaining slots.

In the picture below you see the last space on the wall for a tool in my whole garage.
I do plan to get rid of the gorilla rack shelfing and add wall mounted cabinets to free up floor space. But I don't really have anywhere to add the sub.

What I was thinking was I could just add a new work box in the wall on the garage drywall side and run a pretty short 10/3 romex to the main panel and add the 30a ( future 5hp replacement compressor ready)breaker. Then extend the box and transition to EMT and run 10Ga THHN to the 220 outlet.

It also seems like I will need a cutoff of some sort or are compressors like this always pressurized?

I also added a photo of the wiring of the power to cutoff valve and noticed its 2 hot and ground only. The wiring for it looks iffy to me, seems like the ground should be connected a little more reliably? I was also thinking since 220 kills That this box should probably have come with a cover

All the 220 in my house are Hot Hot Neutral and Ground. Wondering if I should be adding a 4 prong outlet to match or just one to serve this compressor for now?

Thanks for any and all suggestions! Even if they are to contact the AHJ and a Licensed Electrician.

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[Thomas Bank]

I was thinking of adding a sub panel which I have read many have done here but am hesitant due to the "virtual closet" space requirement. Also there is plenty of room for more in my main panel which is pretty close, on the other side of the wall on the outside is my main (square D) panel which has 7 remaining slots.

You should have a disconnect within visible distance from the unit. Basic reasoning is that if someone is working on the unit, someone else going to switch on power will be able to see that the unit is being worked on. I'd have to look in the NEC to see if there is a physical distance limitation there as well. If your main panel is close and in sight of the unit, you can likely get away with just using the breaker there as the disconnect.

It also seems like I will need a cutoff of some sort or are compressors like this always pressurized?

As mentioned, you could use the breaker. I have a disconnect switch on mine.

I also added a photo of the wiring of the power to cutoff valve and noticed its 2 hot and ground only. The wiring for it looks iffy to me, seems like the ground should be connected a little more reliably? I was also thinking since 220 kills That this box should probably have come with a cover

Yep, there should be a cover on that. It should be a "C" shaped piece that clips over the exposed sides. Is the ground just clipped on there? Usually there is a screw through the clip.

All the 220 in my house are Hot Hot Neutral and Ground. Wondering if I should be adding a 4 prong outlet to match or just one to serve this compressor for now?

The only reason for a neutral is for 110V. In your house, things like the dryer and stove have 110V circuits - either for control or for lights or such - while the heating elements are the 220V part. The compressor is 220V only. No 110V circuits. So absolutely no need for a neutral.

[Ron Natalie]

If you're going to keep the plug, that's good enough to use as a maintenance disconnect. Whether you need to turn it off otherwise is largely environmental. I turn my off because my wife will here it if it leaks down enough to trigger the pressure switch in the middle of the night.

[Greg Scull]

So since this is going to be a dedicated 220 outlet I can just run it with 10/2 romex and color the white black at each end? I went to lowes and HD and neither had 10/3 in stock by the foot and I only need like 5 feet not a 25' roll.

[Thomas Bank]

Missed the plug. Ron is correct about that being permissible as a maintenance disconnect. Mine is hard wired, so I needed the separate disconnect. I turn mine off when I'm not in the shop and have a ball valve on the supply line that I close off. That way if something happens the compressor isn't going to run continuously and it keeps the pressure up rather than slowly losing it through .

Yep - 10/2 romex and either color or tape the ends black or red.

[Chip Lindley]

Greg, the coverless switch on your compressor is the pressure switch. Those are factory-set to kick in when pressure reaches a preset minimum, and cut off when pressure reaches the upper limit. You may be able to find the specs. stamped on the switch. The pressure switch contacts double as a motor starter if there is an auto/off lever on it.

No cover means exposed 230v connections. I suggest replacing the pressure switch with one rated for your compressor's tank and motor. Get a PS with the unloader feature and with the auto/off handle.

Also change the oil in the compressor's crankcase. That prolongs compressor life as much as anything.

[Jim Neeley]

One consideration on switching it off that may or may not help you. The air distribution system on my 5hp I-R has a tiny leak in it somewhere and I haven't taken the time yet to find it but, instead of turning off the compressor I close a ball valve on the tank discharge.

While I will eventually get to tracking down the leak, what this does for me is when I go into the shop and open the valve, the tank is already up to pressure and ready to go. And SHMBO is happy since the compressor doesn't cycle at night.

The one time I turned off the compressor instead, when I came back a few days later the tank pressure had dropped significantly and it took several minutes to repressurize the 60 gal tank.

My experience; your mileage may vary!

[John Lifer]

I for one would disconnect with the plug or get a disconnect. In a home shop, how often do you use compressed air? I'd really hate to know I let the thing run all day without stopping if there was leak downstream and I forgot to turn valve off after use. BTW, if you do use often, you need to provide a drain.