How do I hard wire a 230V compressor to a breaker box?

[Guest Magnum Rockwilder]

I just bought a new compressor, and it's 230V.

 

I only have one 230V outlet available, and I need it for my welder, so I want to hard wire the compressor to my garage's breaker box.

 

The compressor has a green wire (ground), and two black wires (positive 120v each). My breaker box has one 30a breaker for 4 electrical outlets and an overhead light, and it has a 60a breaker for the current 230v outlet. The box is supplied from my home's 100a main breaker.

 

Do I need to add another breaker to be able to hard wire the compressor, or can I wire it into the main power supply in the breaker box?

 

Where do I attach the wires?

[jbc3]

I'd put another breaker in and run an outlet for the compressor. Hard wiring into the electrical panel without a breaker is foolish.

What amperage draw is the compressor? Get a __A 2 pole (230V) breaker and a __A 230V outlet.

If you don't have space in the sub panel in your garage, you could wire the welder breaker to an outlet and share the outlet by getting the same plug configuration on both the welder and the compressor, since you likely won't be using both at the same time.

 

Jody

[spotfitz]

I am not a licensed electrician, nor do I play one on tv, but I have run my share of electrical. I have personally seen a friend(electrician, no doubt) get killed from an electrical shock. So, take it for what you payed for it and be especially safe playing with this stuff!

I would not suggest to hard wire the compressor, even though you are on the 100a in the house to this box. You could either use (2) 30a 110v breakers and run this to your compressor(hard wired or plugged) or run (1) 60a breaker to the compressor(again, hard wired or plugged). I personally would run the 60a to a plug. This way you leave room for future add-ons in the box and you now have another 220 plug for use with other equipment if need be. I just hope you have enough current running from the house to this box or you'll always be tripping the 100a. If you're running lights and the welder and the compressor comes on, you'll find out real quick if you have enough for the box!

Hope it helps and remember that even though the pliers your playing with are insulated you can still get burnt.

[BrandonsZ]

The 60A breaker concerns me, unless you have 6 GA wire or better at least, you shouldn't have a 60A braker for your 230V plug.

 

1. The plug probably isn't rated that high.

2. The welder most probably does not need that much amperage at 230V (check the owner's manual)

3. The wires probably could not handle a 60A surge due to short.

4. Your extension cord to your welder probably is not rated to 60A at 230V unless you have one heck of a huge welder.

 

When you are welding at 100A on the professional welders it's not drawing 100A at 230V, the actual voltage is either low voltage DC or low voltage AC.

 

I would check the instruction manual for your welder carefully and put a braker that is close to their recommended one. If they do recommend 60A at 230V then make sure you have wireing and outlets etc. that support that load.

 

I would guess your outlet is rated to 30A and your wire is 8Ga or 10Ga. This is probably good enough for your welder (given you don't have a frekkin huge welder), doubelcheck the manual for the acual braker that you'd need there.

 

As for hard wiring... I'd brake into the wall, and wire up another plug with a seperate braker of either 15 or 20A depending on the recommendations of your compressor. My Sears professional stand up compressor only required 15-20A, I put 20. I have it plugged into where the dryer plug was and that was only a 10Ga wire.

 

If your welder required say 30A at 240V, you better make sure you have 8GA wire and your ground better be up to code. The ground that came with my house was extreamly inadequate.

 

Sorry if this sounds like a lecture, but it sounded weird how you posed this question.

 

Otherwise you could make a junction in the plug you have currently for the welder and add another plug for the compressor. Just don't use them at the same time.

 

If you try to actually run 60A through 10GA wire (if it shorted) I bet that wire would get hot enough to burn off that 1950's style paper casing and when the claims inspector find out you burned your house down because you were running things improperly, you won't get a dime, and your neighbors could probably sue you for endangering their lives and then environmentalists will sue you for causing global warming and the DMV will take your liscence because they can and they felt like it. Then you'll be deported, not for bieng an illegal alien, but because you were "acting like a terrorist".

 

Disclaimer: Hope this helps, I am not a liscenced electrician, so nothing I say here should be taken as fact, so don't sue me.

[Pop N Wood]

Most building codes say a separate breaker must be used for each 220V device. Probably not a bad practice but not always workable. I have a 220V radial arm saw and compressor on the same 20 amp breaker. I just installed a separate 220V switch to turn the compressor on and off. What the building inspector doesn't know won't hurt him.

 

Couple of things. I would not wire the compressor into the 60 amp breaker used for the welder. That breaker is way too big to safely protect the compressor in the event of a problem. In fact, I would be willing to bet that 60 amps is too big for the welder. Most 220 V welders only need 30 amp breakers. For a 60 amp breaker you need at least 4 guage copper wire. My guess is the welder outlet is wired with 10 guage wire, which is only good for I think 30 amps. Might want to go with a smaller breaker on the welder.

 

For the compressor, I would strongly recommend a separate 20 or even 15 amp 220V breaker wired to a 220 volt outlet. The compressor can then be wired to a plug and pluged into the outlet. This gives you a little more flexibility should you have to move the compressor.

 

From what you are saying, I think you have a subpanel in your garage. The garage subpanel should have a breaker in the main box feeding and protecting it. Putting the compressor breaker in the garage subpanel should be fine (if the panel has room for it). Use 12-3 wire to wire up a plug box for the compressor. 12-3 should have a separate black, red, white and ground wire. The white wire is a neutral and the red and black are the two hot wires. The ground wire hooks to the outlet box itself if it is made of metal. The other three wires hook up to the 220V plug receptacle. In the subpanel, the red and black wires hook to the two posts on the breaker (doesn't really matter which way), the white wire goes to the bus bar with all the other white wires and the ground wire goes to the bus bar with all the other ground wires.

 

I am a little hesitant to tell you how to wire the plug wire to the compressor. Usually those things have a red, black, white and separate ground (green) wire. You should have gotten instructions with the compressor. My advice is to follow those.

 

Also a 30 amp breaker on the outlets and light is rather large. Look at the wire hooked up to the breaker. 12 gauge wire should have no larger than a 20 amp breaker. 14 gauge wire should have no larger than a 15 amp breaker. Standard 3 prong outlets are only rated at 15 amps. But, if you feed those with 12 guage wire than you can use a 20 amp breaker. You can use too heavy of wire with a smaller breaker, but not the other way around.

 

Finally, a 100 amp main service is pretty damn small. You sure have a lot of stuff being fed off of that.

[BrandonsZ]

Pop,

 

Yeah, I think 100A service were in older homes (my first and second house had them 1954, 1962), he'll burn the crappy paper wrapping right off his Dryer plug with a 60A braker, probably the same thing if he's plugged into the oven plug. Maybe even cause a fire before that 60A braker ever pops.

[Jolane]

Okay, I will tell you what I am doing, although it may not be for you (I am not responsible either). Actually, you really should consult an electrician first.

My setup is: 1EA 30Amp (10-3 Wire) Twist Lock plug outlet installed below my service panel. I then made up an extension cord using the same connectors, 30ft long out of 10-3 SO Cord. This is set up to run my table saw, my Dynasty 200DX welder, and my Spectrum 625 Plasma Cutter. I will never use all of them at once, so it is not a big deal to have to unplug one to use another. My Mig is just a little 110V unit, but when I get a nice big one, I will also run it off this outlet (most likely). I believe that I have overwired this outlet and extension cord. I don't think I had to use 10 gauge since the duty cycle of the appliances comes into play.

My other 220V outlet is 50A, and is a separate connector coming out of the wall. This is dedicated to my air compressor. The 50A is required for the startup, which draws ~120A (measured with a current clamp)! Running though, it only draws ~26A continuous (true 5 HP). I decided to put a plug because I thought I might want to use this outlet for a welder later on. The Tombstone arc welders do require 50A I believe. I can see why you would have a large breaker for your welder, they can suck the juice!

Without knowing your situation, I cannot recommend a method to hook you air compressor up. At the very least though, mount another box to make your connections to your compressor. Do not connect the compressor wire directly inside the service panel. I would recommend just using the welder outlet you have for your compressor. BTW, the breaker is NOT there to protect the welder or compressor, it is there to protect the wiring between the breaker and the outlet/disconnect! Make sure that the wire is rated for the breaker rating. I believe I used 6 gage for my 50A circuit. Better safe than sorry. As for protecting the compressor, that is the job of the electronics on the compressor (if there are any).

Finally, personally, I would NOT use two breaker for you 220V circuit alone. Make sure that the two legs of the breakers are connected mechanically, such that if one legs trips, it takes the other with it. There are little link bars for this, usually preinstalled on the breaker when you buy one.

I would highly recommend sorting out your wiring first, and making sure that everything is up to par. Be safe, be careful, as the power in the service panel is dangerous stuff!!!

Good Luck,

Joshua

[Guest Magnum Rockwilder]

Okay, I switched some stuff around.

 

The service disconnect says "100" on the switch, and "10,000 a/c" on the breaker itself. The home was built in 1976.

 

Here's what I have going into the shop right now:

 

main power from meter>main disconnect>20' of 10g outdoor wire>subpanel in garage>>>20A breaker feeding 4 110 outlets and overhead lighting, 30A breaker(s) feeding 230v outlet for welder, 30a breaker(s) feeding compressor directly (no outlet).

 

I haven't turned the power on to check it yet. How does that sound?

[Tim240z]

I am doing the exact same thing, so this post is quite timely. This is what I was planning (I will also be speaking to my Brother-in-Law, a general contractor):

I have a 220V outlet that I had installed way back for my welder. My new compressor will be in the shed behind the garage (3/4" conduit pre-run prior to the slab being poured). I will put in a switch up stream of the existing 220V outlet (welder), and run new wire to the shed. The switch will allow EITHER the welder's outlet, or the compressor's outlet to get juice, but not both at the same time. That should satisfy the amperage load issues?

 

Tim

[Guest iskone]

Looks like now is the time for wiring. I myself just installed a 30A 240V outlet for the MM175 I just bought.

 

 

I would just put the same pig tail on the welder and the compressor. It's the fastest and cheapest way to do it. Are you really going to need to run the welder and compressor at the same time? But if your set on a new breaker I would only go upto a 30A for all the resaons BrandonsZ mentioned.

 

Damn Jolane you got a Dynasty 200DX, nice I have been trying to get my work to buy the 300 for a while now, I even know of one for 5K reday to weld and they still won't bite. For some dumb reason they think I only wan tit for my car

 

Isk

[Jolane]

Iskone,

Yeah, I just got the Dynasty a few weeks ago, and finally got the torch kit last night. Now that I can finally play with it, life is good. It really is a nice machine, well, everything but the price anyways. Now I just have to learn how to weld with it..although it is coming right along and is not as hard as I expected. I would feel comfortable welding steel parts for my car with it right now, up to maybe 3/16" or even 1/4". Aluminum doesn't seem too hard either, although I need to practice more before I feel good with it.

 

Magnum, the 100 on the switch is what you care about. The 10,000 is something else. What size breaker is running your subpanel? That will limit your overall current draw. Compressors really use a lot more juice than I ever thought! I never expected to need a 50A for mine, but that was what the manufacturer specified, and now I see why.

BTW, what kind of compressor did you get?

Joshua

[GabeRoc]

main power from meter>main disconnect>20' of 10g outdoor wire>subpanel in garage>>>20A breaker feeding 4 110 outlets and overhead lighting' date=' 30A breaker(s) feeding 230v outlet for welder, 30a breaker(s) feeding compressor directly (no outlet).

[/quote']

 

i have a question, by main disconnect do you mean a disconnect switch or are you speaking of your main breaker panel? if it is the panel, and your 10g wire is connected to no larger than a 30A breaker, you are good to go as far as safty goes. however, if you have just a disconnect switch and you are double lugged or have your 10g wire hooked up to larger than a 30A breaker you are asking for a fire or a burnt wire.

 

i would be hesitant to ok this setup in general because you have a 10g wire (rated to 30A) serving a sub panel with 2 30A breaker plus a 20A breaker. if your compressor will pull 30A (or near to it) when it is running your could very well trip the 30A breaker serving the 10g feed you have going into the garage with just the lights on.

 

a better set up would be #6 wire (rated to 55-60A) or larger running out to the garage with a 50A or 60A breaker in your main box. this would allow for the compressor to run, as well as the welder and lights with little risk of throwing a breaker.

 

tim, assuming you have a compressor that will not draw more amperage than allowed by the breaker going to the current welder, that solution would be fine. but for the cost of a breaker and a few feet of #10 wire why not just give it a dedicated circuit?

 

 

--gabe

[Pop N Wood]

26 amps at 220V = 5720 watts = 7.7 HP. There are some power factor and line loss issues involved, but this should ball park the amperage requirements.

 

A true 5 HP compressor should easily run on a 20 amp 220 V outlet. A 20 amp breaker can easily handle a short lived starting current several times it's rating.

 

As someone mentioned, the breaker must be sized by the gauge of wiring connected to it. No real thought required. They have tables for all this stuff.

 

As for putting too many breakers in the subpanel, I don't know what the laws state but as long as the breaker in the main panel is sized correctly for the 10 ga wire feeding the subpanel, than that breaker should protect you from trying to draw too much current from the welder/compressor/outlets. Still I think it is a good idea to match the 220V breaker amperage to the intended load. Can't hurt and can only help.

 

Keep in mind the plugs themselves have amperage ratings. There is no point in connecting a 20 amp outlet to a dedicated 30 amp breaker. If you need the plug configuration of a 20 amp outlet, then use a 20 amp breaker. Larger wire will actually reduce your power bills ever so slightly, so don't be afraid to go overboard here if you want. As someone else said, upgrading to larger than 10 gauge wire feeding the subpanel wouldn't hurt either. Keep in mind there are different gounding requirements for subpanels than say a dryer outlet. Subpanels must be fed with cables containing separate ground and neutral wires.

 

Another good trick: on your 110V outlets make the first receptical a GFI then daisy chain all of the other outlets off that one. Nice to have GFI protected outlets in the shop.

[Jolane]

Pop N Wood,

With all due respect, I do disagree about a true 5 hp motor easily running on a 20A circuit. I have measured mine running and it is ~26A continuous with the fluke current clamp. At startup, it is ~116A. I think that the part you are missing in your calculations is what the definition of motor horsepower is. There are vacuum cleaners out there that are rated in rediculous power ratings. True horsepower is what the motor will put out when in a normal running state. Peak horsepower (which most vacuums and compressors are actually rated in) is the horsepower of the motor when the motor is stalled. My compressor is rated for a peak HP of ~11.8 IIRC.

I guess I just want to make sure that everyone knows that I have measured mine while it is running, and a 20A circuit would NOT be enough. The manual stated to use a 50A circuit, most likely for startup reasons.

Joshua

[Jolane]

Oh, I just found a table of motor HP (1 Phase) versus Current.

At 5 HP, 230V, current = 28A. I measured my incoming voltage to be ~242V. That would explain why mine draws ~26A.

Joshua

[Pop N Wood]

Hear what you are saying about HP ratings and compressors. Have to be careful. I have a 5 HP "rated" compressor that runs fine on a 20 amp circuit. But admittedly I have not looked into the rating that carefully.

 

All I did above was straight math. One HP is 743 watts, plain and simple. At 220V it means 3 1/3 amps per HP, or about 17 amps for 5 HP. But that would be a 100% efficient motor with no inductive currents causing a larger apparent power.

 

This link

 

http://www.northerntool.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=6970&productId=767&R=767

 

Says the 5 HP Ingersol Rand compressor draws 22 amps at full load. Closer to your number than mine. Guess that means my compressor either isn't fully loaded, has played games with the rating, or something else.

 

Still I remember checking the owner's manual when I wired the compressor to a 20 amp breaker. Follow whatever the manufacturer says to do for the compressor you have. 50 amps circuits are prohibitive for most home shops and a 5HP rated compressor is what most guys will need as a minimum. 30 amps is much more realizable than 50.

 

Good thread.

[Jolane]

Pop N Wood,

I also understand what you are saying about the meth. I realize too that the math assumes 100% efficiency. I think though that what the math is missing is the affect of AC, versus DC. I think what you are calculating is for a DC motor. When you have a 1 Phase AC motor though on 220V, I think you only have power 2/3 of the time, since basically you have two legs going to power the motor out of phase by 120 degrees. This is my thought anyways.

I relate this to welders. If the same welder is used on 1 phase and then hooked up to 3 phase, the power draw is less on 3 phase.

As for being prohibative for most home shops, that may be true. I do have mine in my home garage though, and did not change out the main panel. I am just careful about what I am running at the same time. We use a gas dryer though, which essentially has been replaced with my air compressor load. We do have an electric stove though. I guess the total budget all works out in the end.

I did not check the power requirement of my compressor before I bought it. It was a great deal, I jumped, only knowing it required 220V. I thought it would be easy to just use my 20A circuit I had installed for my table saw. What a suprise it was to see that I needed a 50A breaker! I never would have guessed that! Welders can be decieving too! It was also a suprise when I had to unload all 400# of my compressor from the back of my lifted Chevy Truck with little more than 2 wooden planks and my G/F! That was fun!

Joshua

[Pop N Wood]

220V is the RMS value so it is directly equivalent to DC volts. AC motors do have an issue with the current and voltage being shifted in phase. Hence the inductive "power factor" I mentioned. The voltage and current you measured are RMS values. Multiply them together and you get "apparent power". Multiply that number by the power factor and you get the true power consumed by the motor. But the breaker doesn't care about power, only current, and has to be sized by that value.

 

You taught me that compressor motors seem to draw quite a bit more current than the theoretical value would suggest. Guess I will take a closer look at my compressor's manual tomorrow. Doesn't really matter because it has yet to run out of breath in the 6 years I have owned it. I got it close out at a Sam's club for half what the Sears units were going for.

[Jolane]

Pop N Wood,

I broke down today and asked a very knowledgable EE at work about the induction motor thing. I will try to repeat what he said. Basically, there are two factors to an induction motor that have to be taken into account. The first you covered before, Power Correction Factor. He said that should be on the name plate on the motor, but guess that it might be ~85% for a single phase induction motor. The other is efficiency, which is not related to PCF, which is also ~85% most likely. So,

 

230V * .85 * .85 = 166 V

 

5Hp * 746W = 3730 W

 

3730W / 166V = 22.5A

 

Again, the PCF and the Efficiency are factors of the motor itself, and the 1 Phase power. I am sure the HP rating varies with load, so it looks like either my motor is loaded more (Putting out 14+CFM at 175 PSI), or the PCF and/or efficiency are lower than 85%. I guess both are likely. Also, this is for a true 5HP motor, your results may vary.

Joshua

[Tim240z]

Just to add to the fray. The manufacturer's tag on my new compressor (7hp max, 3.5hp run) states 240volt, 16amp. Now it doesn't say what the starting draw is (I doubt that it is as low as 16amp, but that high draw is momentary).

Anyways, I am running 10 gauge wire to the compressor (about 60feet from the panel).

Tim