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wiring compressor

9K views 78 replies 19 participants last post by  grouch 
#1 ·
I just purchased a compressor with a 15amp 240 v motor.
I have 2 separate 110v circuits close to the compressor.
Can I use the hot leg from each of these circuits to supply 220v?
Logically it sounds correct, but I am not an electrician.
Thanks,
Bob
 
#52 ·
woodz428 said:
... I think stuff like wiring standards still have to be met.
The code is the code and good practice and correct installation procedure and techniques still apply to everyone, homeowner and electrician alike.

Getting back to fire insurance, when a fire occurs and the homeowner wired a circuit that causes a fire, the homeowners insurance may not cover the fire. I would say will not, but I'm sure somewhere there is an exception.

The other side of the coin is why skimp to save a few bucks when the stakes are so high? Would you skimp on the size of your brake lines or take a chance on running bald tires on the highway with your family in the car?

Why do it with a circuit in your garage?
 
#53 ·
bluesman2333 said:
The code is the code and good practice and correct installation procedure and techniques still apply to everyone, homeowner and electrician alike.
I agree fully. the NEC is a minimum code acceptable, and local communities can and do elevate(at least in their mind) any National code. That is the reason I suggested checking the code in whatever location you reside. I don't think you wil find any disagrement on folowing code. I have at least $500,000 of vehicles in my shop at any given time, sometimes a single car of that value( Shelbys are through the roof). I have always found it easier to avoid problems than clean up afterward. :)
 
#54 ·
bluesman2333 said:
No, the problem is having two different loads on one dedicated circuit.
To my understanding, he has a 30 Amp receptacle that is dedicated running #10 wire with a 2 pole 30 Amp breaker.

He will either plug a 30 Amp dryer into this receptacle or unplug the dryer and plug in a welder (with an extension cord) which is supposed to be on a 20 Amp 220V circuit.

So, the problem isn't what you state. And, the problem isn't running the dryer, it is running the welder on a 30 Amp breaker when it is designed for a 20 Amp circuit.
If his extension cord is #10 then he's probably running Romex as an extension cord which is not designed for that.
If he is using a standard extension cord, the largest available for those is #12 and it wouldn't be good to run #12 wire on a 30 Amp breaker.
 
#55 ·
scotzz said:
Actually I will be using a welder that draws 20A. Why is this any different than an appliance/TV/lamp/etc that draws only a few amps from a 120v, 15A line?
The breaker protects the wire.
The feed cord on your 20 Amp welder will be #12 wire. It will not be protected with a 30 Amp breaker and will create a hazard even if your extension cord is #10.
 
#57 ·
roger1 said:
The breaker protects the wire.
The feed cord on your 20 Amp welder will be #12 wire. It will not be protected with a 30 Amp breaker and will create a hazard even if your extension cord is #10.
You are partly correct. Cord and plug connected equipment often has a cord of a smaller gauge than the circuit ampacity. Free air amperages are higher than enclosed amperages. You shouldn't run extension cords for a variety of reasons.

These include voltage drop and overheating of plugs and cord caps due to overload from high starting currents and loose fitting connections. Plugs are by nature loose fitting, otherwise you couldn't insert or remove them.

Hooking an air compressor to a 240 volt circuit with an extension cord is not a good idea.
 
#59 ·
roger1 said:
The breaker protects the wire.
The feed cord on your 20 Amp welder will be #12 wire. It will not be protected with a 30 Amp breaker and will create a hazard even if your extension cord is #10.
roger1..............the specs for the welder say the power cord is a "50A, 250V, Three Prong Plug (NEMA Type 6-50P)." Input is 20A with a recommended fuse or breaker size of "40A Super Lag." Sounds confusing to me.
 
#60 ·
scotzz said:
roger1..............the specs for the welder say the power cord is a "50A, 250V, Three Prong Plug (NEMA Type 6-50P)." Input is 20A with a recommended fuse or breaker size of "40A Super Lag." Sounds confusing to me.
It is telling you to wire the feeder with a 40 amp circuit at a minimum. A super lag is one type of fuse that is able to withstand higher than normal inrush currents. Circuit breakers normally withstand momentary high inrush currents.

If I were you, I would give up on the shared circuit idea and wire in a separate circuit.
 
#61 ·
bluesman2333 said:
It is telling you to wire the feeder with a 40 amp circuit at a minimum. A super lag is one type of fuse that is able to withstand higher than normal inrush currents. Circuit breakers normally withstand momentary high inrush currents.

If I were you, I would give up on the shared circuit idea and wire in a separate circuit.
Yep. Don't fool around.
 
#62 ·
wow that's funny as i thought my post would be like the "last word" however there are two more pages afterwards. y'arr.

to the guy from illinois, yeah, check your local codes, however this whole thing is bootlegged in so isn't getting inspected. as for illinois being the better code i seriously doubt it. it is my understanding that for years and still currently, the city of Chicago has it's own code stating that Romex shall NOT be used in a house and that they are all wired in CONDUIT.

as for this welder thing. code or no code, one thing ALWAYS takes precidence, well, actually, this IS in the NEC, i just aint gonna take the time to find it, and that is this: Manufactures instructions must be followed. period.

also, even if you don't have aluminum service entrance conductors going into your panel, i will bet you my bottom dollar that the Power Companys service drop wires from the transformer are AL. all you have to do is see if the wires coming down from the sky are smaller, MUCH smaller, than the ones after the butt splice to the wires coming out of the service mast. (even if they are both aluminum they are)

just fyi, i have an arc welder. stick, right. and i have used it hard wired into a 30A 2 pole breaker and used it to build my truck chassis and it never tripped. however i never did use an amp meter on it to see if it was getting hot or not. i think in your case you will be okay. just don't quote me if your house burns down. hahahaha. one thing that has always puzzled me is why you have to have a certain amperage circuit, say 20 amps, and when you get into the fixture or appliance you have like 16 ga wire or 18 ga. it would figure those things wouldn't need any more than the internal wires inside are good for, wouldn't it? peace out
 
#63 ·
roger1 said:
To my understanding, he has a 30 Amp receptacle that is dedicated running #10 wire with a 2 pole 30 Amp breaker.

He will either plug a 30 Amp dryer into this receptacle or unplug the dryer and plug in a welder (with an extension cord) which is supposed to be on a 20 Amp 220V circuit.

So, the problem isn't what you state. And, the problem isn't running the dryer, it is running the welder on a 30 Amp breaker when it is designed for a 20 Amp circuit.
If his extension cord is #10 then he's probably running Romex as an extension cord which is not designed for that.
If he is using a standard extension cord, the largest available for those is #12 and it wouldn't be good to run #12 wire on a 30 Amp breaker.
roger1............this "extension" I described is not your typical wire lying on the ground. It is #10 armored cable wired the same way you would run any line in a house. The only difference it that the input end is not wired into the main panel. It terminates in a junction box near the dryer to which I have a standard dryer cord spliced into. I'll post some pics later.
 
#65 ·
bluesman2333 said:
If by armored cable you mean AC cable or MC cable, that is not listed to be portable cordage, hence illegal. Extension cords by nature are unsafe, cords running items drawing large currents are just plain dangerous and a fire hazard.
This is what my set-up looks like. The first pic is the new outlet in the garage (to the left of the 120v outlets). This line runs through the ceiling into the laundry room and terminates at a junction box located behind the dryer. The second pic shows this junction box with a dryer cord spliced in and running out the bottom with the plug end laying on top of the box. In this picture there is a cord already plugged into the existing dryer receptical (on the left).........this is for the dryer. When I want the 240v outlet in the garage I unplug the dryer and plug in the the cord going to the junction box. All is 10 gage wire protected with a 30A breaker.
 

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#66 ·
All I can say is that I have never seen anything like that in my life. I hope your insurance agent or a fire inspector never pays you a visit. FWIW, that is just plain dangerous and illegal. You cannot use an appliance pigtail to complete a circuit like that.

Please, PLEASE change the circuit to one that is safe and meets code.
 
#67 ·
bluesman2333 said:
All I can say is that I have never seen anything like that in my life. I hope your insurance agent or a fire inspector never pays you a visit. FWIW, that is just plain dangerous and illegal. You cannot use an appliance pigtail to complete a circuit like that.

Please, PLEASE change the circuit to one that is safe and meets code.
bluesman2333................I appreciate your input regarding my set up. You say it is dangerous but please provide the engineering rationale for your reply. Quite honestly I dont see it.........wire size and breakers all match...........tell me why it is a problem.........other than what the code says.
 
#68 ·
I am amazed. All the electrical experts giving advice and opinions to the OP and not one of them has addressed the original question :

have 2 separate 110v circuits close to the compressor.
Can I use the hot leg from each of these circuits to supply 220v?
The answer is maybe. IF each "hot" leg is from the same side the incoming line then NO.
If each "hot leg" were to be from opposing sides of the incoming line then YES.
Is this legal? I don't think so.
Is it safe, I have no idea.
Would I do it, NO.

What you did may or may not meet your local code- call and ask if you want the correct answer.
You are correct in your thinking about the 30 amp breaker with a 20 amp load. No different than a 15 amp breaker and a 3 amp load in a household circuit throughout your house.
The circuit breaker protects the wire in circuit NOT the appliance at the other end of the wire.
As long as the wire size is correct for the breaker rating you are fine. Can the wire be larger than the breaker rating, certainly.
IMHO, and it is only my opinion, if I had your wiring setup in my house, I would sleep fine.

Is your insurance valid, I have no idea, ask your agent.

I believe you could modify your setup and pass an inspection. You would need to route the incoming power line into a properly sized manual dpdt break before make switch with one side feeding the dryer recepticle, the other side feeding the cable to the aux. outlet. But that again is only my opinion, ask your inspector.

I am not an electrician and I did not stay at a Holiday Inn Express last nite.
 
#69 ·
scotzz said:
bluesman2333................I appreciate your input regarding my set up. You say it is dangerous but please provide the engineering rationale for your reply. Quite honestly I dont see it.........wire size and breakers all match...........tell me why it is a problem.........other than what the code says.
It's more than the code. First, the code is the NEC, National Electrical Code, an ANSI standard. This is a document produced by the NFPA, National Fire Protection Association every three years. States and local municipalities adopt this and make it a statute. Local AHJ's, Authorities Having Jurisdiction, enforce the code and ensure compliance.

So, the code is a minimum standard written to minimize fire and death risk in structures and other occupancies, think of it as a minimum law you are required to build to.

Now, in the code, are three little gems concerning installations. One, all work shall be done in a workmanlike manner. Two, all components of an electrical installation shall be listed for the use by a NRTL or Nationally Recognized Testing Laboratory. Examples of NRTL's are UL, CSA, or ETL. There are others. Three, you have best practices. Best Practices is subjective and subject to an inspectors interpretation. What you can get away with in podunk you might not get away with in Chicago or New York.

So, looking at that pigtail, it is listed as an appliance cord. It's intended use is only for use in conjunction with an appliance. It is not allowed for use as you have installed it because it is not listed for that use.

By your logic, you can take a piece of brake line, wrap it with cardboard and stuff it in a piece of pipe and use it in your circuit as a current carrying conductor. It works, right? No, it needs to done according to code. It is not "just" the code. It is part the National Life Safety Code.

Obviously this is the internet and you are far away. I've actually helped people before for free because like you, they did something dangerous and I had a real worry they were going to burn to death some night in a fire. Do what you like of course, but my whole purpose in writing any response in this thread was to educate you and try to get you to see why it is important to do things right, just like you would in your classic car.

I sense you are looking for third party justification for your installation, but the fact remains that you just plain did it wrong and it could have serious consequences.

@Old Fool, you are right, this thead did get highjacked some. :D
 
#70 · (Edited)
bluesman...........you do not understand the intent of what I am doing.......I fully understand that that my set-up is not to the NEC or any other code. What I am doing is being creative the same way as many on this site are doing with cars............mixing and matching parts and solutions to produce something that works and is safe. I fully appreciate your knowledge of the electrical code but I am showing my temporary solution to the fact that I don't have space in my main panel for another line.

To cut through all the BS....................bottom line from MY perspective...........a #10 wire carries 30 amps safely.....solid or stranded, regardless of sheathing.......show me the ENGINEERING REASON, how 30A or 20A is different from a dryer, welder, compressor or heater (other than duty cycle). The code as you state says that a cord for a dryer must be used soley for a dryer but I say that # 10 is #10 and it don't make a damn bit of difference what is on the other end (assuming of course the draw is 30A or less). I am simply using an electrical cord designed to bolt up to to a specific application and ADAPTING it for use with another, similar to what many are doing with cars. I say that as long as wire size and connections are correct what I have is safe. However, I am open to any engineering evidence that says otherwise.
 
#71 ·
scotzz said:
bluesman...........you do not understand the intent of what I am doing.......I fully understand that that my set-up is not to the NEC or any other code. What I am doing is being creative the same way as many on this site are doing with cars............mixing and matching parts and solutions to produce something that works and is safe. I fully appreciate your knowledge of the electrical code but I am showing my temporary solution to the fact that I don't have space in my main panel for another line.

To cut through all the BS....................bottom line from MY perspective...........a #10 wire carries 30 amps safely.....solid or stranded, regardless of sheathing.......show me the ENGINEERING REASON, how 30A or 20A is different from a dryer, welder, compressor or heater (other than duty cycle). The code as you state says that a cord for a dryer must be used solely for a dryer but I say that # 10 is #10 and it don't make a damn bit of difference what is on the other end (assuming of course the draw is 30A or less). I am simply using an electrical cord designed to bolt up to to a specific application and ADAPTING it for use with another, similar to what many are doing with cars. I say that as long as wire size and connections are correct what I have is safe. However, I am open to any engineering evidence that says otherwise.
I agree, citing code is not the science behind the code, explain the physics behind the code (if there is a science behind the code).

I believe many times a UBC is implemented to keep a problem from happening and is a "universal" solution .
For example using the dryer pigtail as the op has.
IF the wire size,plug and receptacle are all rated at the appropriate amperage there is no superlicious risk of using it.
The problem most likely came about somewhere sometime in the past where the hard wiring was up to the job at hand but some one put an undersized cord on it, assuming it would be ok because it was "big". (as in where the manufacturer use an extra thick covering to hide the fact there is little copper wire inside).
The easy way out was to write code to state NO mismatched use of pig tails, much simpler to write and enforce then to state an exact requirement for each installation.
A good example of safe but illegal is to put a 15 amp cord cap on a piece of 12-3 romex and terminate the other end in a box with a 15 amp receptacle for use as an extension cord. ( used to be common on construction work sites)

It is illegal to cut the end cap off an extension cord and add a box.
The box can be of proper construction, properly connected, properly grounded, and it is still illegal.
Why? Because you cannot safely assume the electrician that made the cord did it correctly and therefore an unsafe condition with its construction could exist.
It is assumed that an identical cord produced by a manufacturer is always properly manufactured.(who knows what the Chinese actually do)

Imo, there will be no final word on this topic, the code guys will pound their code books, and no one is going to say the installation is safe.

I think and it is just my opinion that the op has used a bit of ingenuity and thought to make a workable "hotrod" solution.
 
#73 ·
I think the bottom line here is that, if for some reason a fire did happen and an investigation of the cause of the fire came back to that wiring, then insurance may not cover the damage the fire caused.
Same for if someone got shocked and hurt or killed from that wiring plus he could be liable as well.

If he feels confident nothing will ever happen, then he can take that risk and do what he is doing.

It's always best to do wiring to code. It's not that hard and it's not that expensive.
 
#74 · (Edited)
bluesman2333 said:
Yea, I decided I'm not going to respond anymore. People looking for justification for their work will argue until the day they die in the fire that the dangerous and illegal work started.
I never asked for "justification"...........just wanted constructive input for the application that I devised.................similar to the "hotrodding" applications that this site is devised for. Obviously you are a union electrician that goes "by the book".............again........I am not doing that.

My house will not burn down...........I am comfortable with that......why? Bcause I understand wire sizes/breakers and loads..........not just what he "code" tells me. I am comfortable that my set-up is OK ...........and as confirmation I offer 30 years of doing my own 110/220v home wiring.

I question your knowledge of home wiring as you have never offered a single technical fact to back any of your statements. In all honestly I would feel very unsure of any electrical work I did if I my only source of confirmation was a book (the code) to tell me what to do. Why?..........because then I would have no idea of what I am actually doing...........just going by a "code"......no technical knowledge.....pretty scary. If you understand the realtionships of wire size/load, you are comfortable with designing a system "not from the book" (gee...just like a brake system). Just so you know..........I am a Mechanical Engineer by trade..............and basic home wiring is no sweat.............so don't try to use the "code" to shoot down my solution.
 
#76 ·
If you are willing to risk the value of your house against that never failing, go for it. Just because something works, doesnt make it right or safe for that matter. It is sometmes a real pain to pull wire but you ned to weigh it against the risk. If you did have a fire in your garage that would be the first thing looked at and may be blamed even if it was not the cause.
Why not put a junction box before the drier and connect both plugs with the proper size romex. As long as the circuit breaker is sized properly and you dont run both items at the same time you will have no issues. If you forget and try to run both the breaker will trip and no harm done.
 
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