Greetings. I've done quite a bit of 110 wiring and some 220 but I'm a bit weak in that area. I've got a new 60 gallon 220V air compressor that is now located in my garage approximately 50 feet from the house which is where the main breaker panel is located. There is no room to add another 220 breaker or in any way add an additional separate circuit without adding a sub panel. I've purchased a two pole 30 amp breaker and matching sub panel and need to wire it into the existing main breaker panel. Most 220 circuits I've seen previously are either 3 or 4 wire configurations however the motor for my compressor is a 2 wire plus a ground setup. I've run the appropriate length of 10/2 outdoor NM wire from the compressor to the location where the sub panel will be installed. What I need to know is the connections that need to be made. There was previously a hot tub 220 circuit but it was removed when the hot tub was relocated to my sisters house however on each leg coming in from the meter there is a copper lug with a set screw that look to have been added and are not used by any other circuit. I think possibly this is where the hot tub wiring was connected but am by no means certain. What I really need to know is, since I need 220 but will have no third wire for a neutral, and I know this is how it needs to be and have read a good deal about this type of connection but can find no schematics or specific connection instructions, do I simply hook one wire from each incoming leg to each of the breaker connectors in the sub panel, and then do the same on the opposite side of the breaker using the wiring that runs out to the compressor, and just not use a neutral at all, and connect my bare ground wire to the neutral bus in the main breaker panel? Any help, additional information or diagrams will be appreciated. Comments to the effect that you can't run 220 without at least 3 wires plus a ground wire, will not, as I already know that's untrue. Thanks in advance.

 

The National Electrical Code requires that a sub panel in a remote location be equipped with a bond wire in addition to any current carrying neutral. If you do not run any 120 volt loads, you can do this (legally) with 3 wires. I believe you have it right from the way you wrote the question except that the naked wire goes to case ground of the sub box, not the neutral strip, unless you see where a place has been provided to attach the neutral strip to the metal box. Two legs of "hot" go through a double breaker and the naked wire serves as the safety ground (what electricians call, "bond").

I hope this clears it up for you.

 

darkbreeze: Just to ask something obvious: is there also 120V wiring to the garage?

I'd hate for you to do a bunch of work to add the compressor then realize you also need other power for other tools. It would be easier to add everything together.

 

Yes, there are already 110 outlets in the garage, just no 220 ones. #12, the sub panel is going to be right beside the main panel, and then the wires will run from the sub panel to the garage, so it isn't really remote, which is why I thought I'd just connect my ground to the bus in the main panel instead of in the sub panel since it's only about a five inch difference but I can run a ground from the bus in the sub panel to the bus in the main panel and then connect my ground running out to the garage to the bus bar in the sub panel instead of the main if that's how it needs to be done. It's not much if any more work anyhow to do it that way. I'm not familiar with the term "bond" but I'm guessing you are in fact talking about the ground wire which is bare and interconnects all locations with a safety ground. Thanks.

 

Here's what I'm assuming I need to do. Please feel free to correct any incorrect assumptions if I'm wrong. Thanks.

 

That ground terminal in the sub-box looks like it does not connect to the metal box. If it does connect to the metal box, you are good to go.

I think you need an explanation of, "bond". Neutral is a current carrying wire that has nearly zero volts on it (compared to earth ground). The bond wire never carries current except in case of a fault condition. It is true that in most breaker boxes, the neutral wires and the bond wires are connected to the same terminal strip. It's when you go to remote buildings that you have to make clear the difference between a current carrying ground and a bond wire, sometimes called, "case ground" or, "earth ground". In your case, you are not supplying a neutral conductor. You are not providing a current carrying wire that is connected to zero volts. You are providing a bond wire, and all metal cases must be connected to the bond wire. That includes the little sub-box that you provided and the metal case of the compressor and its motor.

The point is, a neutral wire that is carrying current will have a small voltage on it caused by the current flowing through it times the resistance of the wire. If you connect this current carrying neutral to the metal boxes, they will have a small voltage on them when any 120 volt loads are running. You can get a "tickle" from that if you grab the box and your bare feet are on concrete. The bond wire, not carrying current, will not develop a tickle voltage when machines are running. That is the wire that you want connected to the metal parts that people can touch.

 

That ground terminal in the sub-box looks like it does not connect to the metal box. If it does connect to the metal box, you are good to go.

Correct. I do believe I see at least one green wire, and one bare wire on that terminal block on the left side . Either of those designate that as a ground bond block, which is the correct place to connect for ground.

The terminal block on the right side appears to have several white wires on it, which indicates it as the neutral connection block, thus not the place for your 3rd wire.

 

Just to clarify, the 3-wire 220V configuration includes two hot connections and a ground. The 4-wire 220V configuration includes two hot connections, a neutral, and a ground. The neutral is for anything that may need 110V, using one of the hot wires and the neutral.

 

I've got another question. I finally received some replies on another forum I posted on prior to posting here, and there are a couple of guys trying to tell me that I cannot run a 220V circuit to my garage because I already have a 110V circuit running to the garage. The garage is remotely, 50 ft, located from the house. They say that only ONE circuit can run to any outbuilding. This can't be accurate. I mean, I guess it can be, but it makes no sense. I had an additional circuit added to my other outbuilding last year, by a certified electrician, and had it inspected, and they never said anything like that or indicated it was a problem. ?????

 

I've never heard of that.

It would be nice if you posted a sign that said, "There is more than one circuit breaker supplying this building" but I don't think there is a law about that, either.

 

...I finally received some replies on another forum I posted on prior to posting here, and there are a couple of guys trying to tell me that I cannot run a 220V circuit to my garage because I already have a 110V circuit running to the garage...

Interesting on it's own. I'm not certified in any way concerning the NEC (the CODE). I just have a more then casual interest in it and have spend some time reading it.

When someone posts something like this I would ask then exactly what section you are violating. If they have an answer it will be something like "article 300.7 states you need seal the conduit running into a walk in freezer to prevent condensation." The number states the chapter (3) article (300) and section (2) where condensation is discussed.

If they just say "the code" then they usually be ignored. Someone who really knows will crack the book (or load the pdf) and answer a straightforward question with the section reference number.

You can view the code book online for free.

 

Yeah, I'm trying to find out that answer myself but haven't gotten any response yet. They seemed knowledgeable but some things seem kinda off too like maybe Canadian or European code.

 

Well, it seems they are correct. According to section 225.30 of NEC anyhow. Is it possible my local standards are different? I know there are two separate feeds to my woodshop building and I know both feeds were done on separate occasions, and that it was inspected and signed off on so how could this be if it was a violation.

 

Good reason why I never heard of that...my book is from 1981 and it only goes to 225-25.

I might have to move into the 21st century some day

 

Hi darkbreeze,

I see you're connecting directly to the bus bars running from the main breaker. 100A? 200A? Are you sure this is allowed?

If you do do this then be sure to use at least #8awg wire for the hot wires and the bare ground. For 200A use #6.

If there should be an accidental short between the two hot, or from hot to ground in the sub-panel then you want to trip the main breaker smartly, and not heat up too small of guage wires to melting point and possibly set fire to your panel. Keep the runs as short as possible.

Play safe,
Ifixit

 

Well, it seems they are correct. According to section 225.30 of NEC anyhow. Is it possible my local standards are different? I know there are two separate feeds to my woodshop building and I know both feeds were done on separate occasions, and that it was inspected and signed off on so how could this be if it was a violation.

It is quite possible your local code is different. While it is typical for a locality to approved the NEC code in it's entirety, this is rarely done in a timely manor, meaning while the most current NEC code book is 2011 your locality may still be on 2008 or even earlier.

However, it always comes down to the inspector. If one gives a good argument as to why something must be done a certain way (and it is safe!) he may still sign off on it.

=====
I have a link up there that allows one to view the current and past codes. From 2011 (and since no substantial changes 2008 also):

225.30 states (paraphrased) a branch circuit on the load side shall be supplied by only one feeder... unless permitted by 225.30 A thru E.

225.30D Different Characteristics. Additional feeder or branch circuits shall be permitted for different voltage...

225.30E ... shall be permitted ... where documented safe switching procedures are established and maintained for disconnection.

Again, I am not a code expert but this sounds like the permissions you need. "D" may stand alone, "E" would just be a sign in the garage stating the shut off is in the house (duh!).

Ultimately your local inspector would be the judge.

 

The first problem I saw in your picture, you are attaching to the buss bars which means the wiring going to the garage will be fused at 200 amps. In other words, they are not fused and a short in those wires would cause them to burn up.
That is what your buss bars are fused (breakers) at, what you must do is insert a 2 pole breaker in the house panel and tie to that. Second, if you put a sub panel in the garage 2011 code states for a 220/120 panel you must have two hots, one neutral and one ground, you must also drive a ground rod at the sub panel and the the ground must be isolated from the neutral.

I know you said you only wanted to wire the comptressor (220v), but I believe you'll find that you wished you put a neutral in there for more 120v circuits.
If it were me I would run a 220/120 60 amp panel and do away with the other.

 

gerty raises a good point that the wire between the main breaker panel and the new sub panel needs to be rated for 200 amps as that is the current limiting device in that leg. The #10 from the sub panel to the load is fine for the 30A side but to carry 200 A you need to jump up to I believe 3/0 cable, or the same size as the service wire entering the main panel.

I hope they are close together.

 

gerty raises a good point that the wire between the main breaker panel and the new sub panel needs to be rated for 200 amps as that is the current limiting device in that leg. The #10 from the sub panel to the load is fine for the 30A side but to carry 200 A you need to jump up to I believe 3/0 cable, or the same size as the service wire entering the main panel.

I hope they are close together.

All he needs to do is snap in an appropriate size breaker in the main panel for the subpanel feed and connect to it.

 

All he needs to do is snap in an appropriate size breaker in the main panel for the subpanel feed and connect to it.

In his first post he states the main panel is full up, and he also states no need for 120V lines as they already exist.