[68Datsun510]

Hello folks, new here on the forum, and relatively new to the world of AC power and the rules associated with it. I have a good background with rewiring cars from the ground up, but thats DC, hard to really hurt yourself with a car electrical system.

I just picked up an old craftsman 220V air compressor off craigslist, very nice piece, however, i also use a 220V dryer. THere is only one 220v plug in the garage. Obviously it would be foolish to drag the dryer out every time i need compressed air, and i wouldnt be stupid enough to try and run a compressor and the dryer at the same time. So, I need to build a splitter somehow.

I need a male 3 prong dryer cable on one end, and both a female 4 prong dryer end AND a female NEMA 6-20R connector.

I have a problem, I am renting my house, a nice little place, but I find it hard to believe the landlady would be down for adding additional outlets around the garage.

Here is a diagram of what I would LIKE to do, please critique me in any way possible as I want this to be SAFE above all else!

 

[thegonagle]

I don't see a way to do it safely. The grounding is what gets you.

DO NOT use a drain pipe as a ground--unsafe! Copper cold water supply lines are theoretically grounded, but are not a substitute for a ground conductor that runs to the panel, so although it's "safer" than a drain pipe, don't that either.

If there was a 4-prong dryer receptacle, I would have some suggestions which would yield the safest temporary setup possible (it would NOT meet code, but could conceivably function safely), but unless you can do something about the 3-prong receptacle in the wall, there's no way it can be safe "above all else."

 

[68Datsun510]

Ok, so, hypothetically if it were a 3 wire dryer, no ground wire issues, then...??? ANd for the compressor, I assume the ground wire would go to the 90 degree kinked pin on the 3 wire dryer cord? Neutral? I believe?

 

[68Datsun510]

BTW thank you for your input!!!

 

[theatretch85]

Ok, so, hypothetically if it were a 3 wire dryer, no ground wire issues, then...??? ANd for the compressor, I assume the ground wire would go to the 90 degree kinked pin on the 3 wire dryer cord? Neutral? I believe?

That 3-wire dryer connection has a Neutral connection, not a Ground connection. You would still theoretically have issues with your grounding. Creating the splitter and connecting the ground prong of the 6-20R to the dryer circuit would potentially put return current on the ground of that compressor. So in the event your body happens to make a better path to ground than that neutral wire in the wall, that dryer could be using your body as that return path. This is why neutral and ground are only tied together at the service equipment (usually main circuit panel).

Your best bet is to see about replacing the 3 wire receptacle to a 4 wire. Then you could make a splitter that has a ground connection to your compressor, and a neutral and ground connection to the dryer (of course with a 4 wire plug, and cord on the dryer).

 

[kbsparky]

This is NOT a good idea, especially in a rental property.

This is fodder for starting fires.....:furious:

 

[InPhase277]

The harsh reality is that what you propose, while it will work, is some jackleg doo doo.

One issue is grounding. There is no ground, and grounding to a pipe is also bunk. Another issue is the 6-20R and #12 wire on the 30 A dryer circuit. The grounding issue isn't so bad because the circuit is likely dedicated. And if it runs back to a main breaker panel where the main bond is, then effectively the neutral is only a neutral when the dryer is running, and when unplugged is the same as any ground wire.

The only way to leave the circuit intact and still do this in a non-jackleg manner would be to have the capability to un-plug the dryer and plug in a fused adapter. Having both plugged in at the same time is the no-no, due to neutral current and the potential to energize the frame of your other equipment. Maybe make two adapters. One that extends the dryer receptacle to an accesible location, and another that converts the 30 A circuit into a 20 A circuit for the other equipment.

 

[Bigplanz]

Some of our more qualified members have already covered this from a 'will it work/is it safe' point of view. From a regulatory point of view, if any of our inspectors saw this, they'd make you take it out on the spot or have the power company disconnect the power to the house until you did. (We had a child killed here a few years ago in a garage with a cluster f*** wiring job, and we've had a zero tolerance policy ever since.)

 

[Speedy Petey]

As the others have stated, this is wrong on many levels.

a) No ground exists, only a neutral.

b) You CANNOT have a 20A receptacle on a 30A circuit. Period.

c) Rental. DO NOT touch anything electrical there. :no:

 

[68Datsun510]

This is exactly why I came here. Thanks folks for the education!

 

[68Datsun510]

So, how much do you guys think it would be to have an electrician install a 6-20 outlet in the wall right next to a 120v plug with the dryer plug directly below?

Do they install a new line from the fusebox, or do they tap off the dryer power and connect to the 110's ground?

 

[Bigplanz]

Do they install a new line from the fusebox, or do they tap off the dryer power and connect to the 110's ground?

A separate line is needed. A 20A socket and a 30A socket cannot both be connected to the same 10 gauge wire, as the possible load is 50A.

If they are on the same circuit, you have to assume they will be used at the same time.

 

[Gigs]

A separate line is needed. A 20A socket and a 30A socket cannot both be connected to the same 10 gauge wire, as the possible load is 50A.

If they are on the same circuit, you have to assume they will be used at the same time.

This logic is all wrong. I mean your heart is in the right place, but the logic is wrong.

If you take that logic to its conclusion, then you can't even use duplex 15A outlets because they could put 30A of load on the 15 amp circuit.

 

[Speedy Petey]

This logic is all wrong. I mean your heart is in the right place, but the logic is wrong.

If you take that logic to its conclusion, then you can't even use duplex 15A outlets because they could put 30A of load on the 15 amp circuit.

I was going to post something similar, but it just easier to say I completely agree. :thumbsup:

 

[68Datsun510]

Yeah, would NEVER attempt to run a dryer and compressor at the same time, my parents have an old sears oilless compressor and i cant even have a flood light on when its running or the breaker goes.

 

[Bigplanz]

This logic is all wrong. I mean your heart is in the right place, but the logic is wrong.

If you take that logic to its conclusion, then you can't even use duplex 15A outlets because they could put 30A of load on the 15 amp circuit.

110V general purpose 'convenience' sockets are intended to serve many different devices, from a 0.25A clock radio to a 15A space heater. Put too many high amp draws on the circuit and it will indeed trip the breaker, but usually even with several devices running the circuit is well within its design specifications.

240V circuits are a quite a different animal. Each socket design is 'dedicated' to a certain level of current. A 30A socket is for a dryer, for example, a 50A for a range, etc. There aren't any 0.25A, 240V clock radios.

It is an interesting question. Should a 240V circuit be designed for the highest amp dedicated socket it has on it, or for the possible amperage of the sockets, total? Personally, I have never seen a 240V circuit with more than one socket; though it is theoretically possible to have one and code doesn't prohibit it. Since most (all?) 240V devices I am aware of draw an amperage close to their rated maximum when operating at full capacity, I would think it would be a bad idea to have a 20A and 30A dedicated socket on a circuit protected with a 30A breaker even if it is within code to do so. As I am certainly not an electrician, I defer to others as to whether this is an acceptable wiring practice. I would be interested in hearing from our more knowledgeable members in regard to whether this (multiple 240V sockets on a single line) is a common in a single family residential setting.

 

[Speedy Petey]

I'll just address a couple of these:

110V general purpose 'convenience' sockets are intended to serve many different devices, from a 0.25A clock radio to a 15A space heater. Put too many high amp draws on the circuit and it will indeed trip the breaker, but usually even with several devices running the circuit is well within its design specifications.

240V circuits are a quite a different animal. Each socket design is 'dedicated' to a certain level of current. A 30A socket is for a dryer, for example, a 50A for a range, etc. There aren't any 0.25A, 240V clock radios.

True, but this is circuit design issue.
120v "general use" receptacle are meant to be used as you describe.
Not all 240v receptacle circuits are as you describe, they can be installed with the same intention as 120v general use circuits. Each receptacle is NOT 'dedicated' to a certain level of current unless the circuit is designed that way.

Personally, I have never seen a 240V circuit with more than one socket; though it is theoretically possible to have one and code doesn't prohibit it.

Commercially this can be pretty common, and is most certainly code legal.

Since most (all?) 240V devices I am aware of draw an amperage close to their rated maximum when operating at full capacity,

EVERYTHING "draw(s) an amperage close to their rated maximum when operating at full capacity". Not just 240v loads.

will I would think it would be a bad idea to have a 20A and 30A dedicated socket on a circuit protected with a 30A breaker even if it is within code to do so. As I am certainly not an electrician, I defer to others as to whether this is an acceptable wiring practice.

Well, I did state earlier that you cannot have a 20A receptacle and a 30A receptacle on the same circuit. That definitely IS an issue. But you can have multiple 15's, 20's, 30's or 50's on one circuit.

I would be interested in hearing from our more knowledgeable members in regard to whether this (multiple 240V sockets on a single line) is a common in a single family residential setting.

Common, no. Legal and done on occasion? Absolutely.
I have seen and done it personally. I have had customers with several Eurpoean kitchen appliances and needed multiple locations to put them.
I have had the exact same issue with residential workshops.

 

[micromind]

I have about a half-dozen 20 amp 250 volt receptacles in my garage, all on the same 20 amp two pole breaker. There's also 4-50 amp 250 volt receptacles, all on the same 50 amp two pole breaker. There are also about a dozen 30 amp 250 volt 3 phase receptacles, all on the same 30 amp 3 pole breaker.

As stated above, rare for a house but common in commercial/industrial settings.

There are different code rules for a single receptacle and more than one on a circuit. A single receptacle can be fed with any size breaker that doesn't exceed the rating of the receptacle. More than one receptacle must be fed with a breaker that matches the rating of the receptacle, with two exceptions. These are; 15 amp receptacles can be fed with a 20 amp breaker, and 50 amp receptacles can be fed with a 40 amp breaker.

About the only code requirements I can think of that apply to only 125 volt receptacles are GFI, and AFCI.

Rob

 

[Bigplanz]

Thank you for your detailed answer. It was very informative. Just a couple of clarifications, and then I'll tell you what the building permit supervisor told me this morning when I asked him about these issues.

I'

EVERYTHING "draw(s) an amperage close to their rated maximum when operating at full capacity". Not just 240v loads.

I was a little unclear on what I intended to say. Basically, a 240V appliance is more likely to be drawing close to the full capacity of the circuit every time it is operating at full power. A dryer pulls close 27A when the heating element is on. My intention was to explain why a 240V device is usually on it's own circuit. There 'usually' isn't any headroom left for anything else to run on the circuit without tripping the breaker when the appliance is running a full power.

When I got to work today, I ran into a supervisor in commercial/residential permitting. I asked him:

"What if somebody has 10/2 running to a garage for a three-prong dryer and they want to 'split it' to add a 20A 240V receptacle for a compressor. They couldn't run them at the same time, of course, but how could they legally do that."

He said, "let me look it up, I'll let you know.:

Later he said, "Well, you can't do it with 10-2 because that's not an acceptable wiring method for 240V anymore. It's grandfathered for the existing dryer, but any change has to be brought up to current code which is 10-3. You could run a separate ground from the main panel, but we'd require it to be in the same conduit as the 10-2, so that's not really practical. Might as well upgrade the service."

"If it was 10-3 you would need a sub-panel in the garage, with a 30A main, a 30A double pole for the dryer and a 20A double pole for the compressor."

He then went on to say that a dryer and a range both needed a dedicated breaker, just for them, but that multiple sockets could be approved on a single 20A, 240V breaker.

I recall an earlier thread where I stated a dryer had to be on a separate circuit breaker, and it was pointed out, "not according to the code." I looked through the NEC myself, and can find no such requirement. However, at least in Louisville, I was correct, a dryer and range must be on its own breaker, with nothing else.

Hey, don't kill the messenger. I'm just telling you what the supervisor of commercial and residential permitting told me.

 

[Speedy Petey]

I was a little unclear on what I intended to say. Basically, a 240V appliance is more likely to be drawing close to the full capacity of the circuit every time it is operating at full power. A dryer pulls close 27A when the heating element is on. My intention was to explain why a 240V device is usually on it's own circuit. There 'usually' isn't any headroom left for anything else to run on the circuit without tripping the breaker when the appliance is running a full power.

We'll just have to respectfully disagree on this one.
Sure, a dryer pulls 27+ amps, but what about a 18k BTU A/C? That would be a 240v circuit, but would only draw about 9 amps at 240v. This is no where near "full capacity" on a 15 or 20 amp circuit.
I think you are just interpreting that it is normal to have a load near it's circuit's capacity because it is simply cheaper that way. Why run a 40A circuit on #8 when a 30A circuit on #10 is perfectly fine. Tne again, this is just one example. Like my 18k BTU A/C, not nearly all loads are that close to full circuit capacity.

When I got to work today, I ran into a supervisor in commercial/residential permitting. I asked him:
"What if somebody has 10/2 running to a garage for a three-prong dryer and they want to 'split it' to add a 20A 240V receptacle for a compressor. They couldn't run them at the same time, of course, but how could they legally do that."

He said, "let me look it up, I'll let you know.:

Later he said, "Well, you can't do it with 10-2 because that's not an acceptable wiring method for 240V anymore. It's grandfathered for the existing dryer, but any change has to be brought up to current code which is 10-3. You could run a separate ground from the main panel, but we'd require it to be in the same conduit as the 10-2, so that's not really practical. Might as well upgrade the service."

"If it was 10-3 you would need a sub-panel in the garage, with a 30A main, a 30A double pole for the dryer and a 20A double pole for the compressor."

Again, this is due to the fact that a 20A receptacle cannot be on a 30A circuit. This has nothing to do with multiple receptacle on a circuit.

Also, you can tell your supervisor that 10/2 was NEVER legal for a 120/240v dryer. 10/3 without ground was legal for many years, but an insulated neutral in NM cable was always required. If you see 10/2 to a dryer it was a non-compliant installation from day one.

10/2 is "accepted" and perfectly legal for a straight 240v load. It was never legal for a 120/240v load.