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Old 05-14-2009, 04:48 AM   #16
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Quote:
Originally Posted by Gigs View Post
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.

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Old 05-14-2009, 07:37 AM   #17
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I'll just address a couple of these:

Quote:
Originally Posted by Bigplanz View Post
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.





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Originally Posted by Bigplanz View Post
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.




Quote:
Originally Posted by Bigplanz View Post
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.




Quote:
Originally Posted by Bigplanz View Post
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.




Quote:
Originally Posted by Bigplanz View Post
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.
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Old 05-14-2009, 08:36 PM   #18
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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.

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Old 05-14-2009, 08:40 PM   #19
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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.

Quote:
Originally Posted by Speedy Petey View Post
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.

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Old 05-14-2009, 08:57 PM   #20
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Quote:
Originally Posted by Bigplanz View Post
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.





Quote:
Originally Posted by Bigplanz View Post
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.
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Old 05-14-2009, 09:14 PM   #21
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Originally Posted by Speedy Petey View Post

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.
George isn't my supervisor. He's one of the supervisors in permitting. He does mostly commercial, but also multifamily residential. Another guy is the supervisor for single-family residential. I am a supervisor in planning and design, and our code is related to, but separate from, the building/electrical/plumbing/HVACR codes. That's why I 'sort of know' a little bit of everything. Just enough to make me dangerous.

This is the code I work with daily.

http://www.louisvilleky.gov/Planning...CMarch2006.htm
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Old 05-14-2009, 09:25 PM   #22
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Originally Posted by micromind View Post
About the only code requirements I can think of that apply to only 125 volt receptacles are GFI, and AFCI.
Also the 12 inch burial depth exception for 125v GFCI protected buried circuits.
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Old 05-14-2009, 11:14 PM   #23
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won't it be less of a headache... and cheaper... to just go buy a 110v pancake compressor??? $150 and you're done.
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Old 05-15-2009, 07:37 AM   #24
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won't it be less of a headache... and cheaper... to just go buy a 110v pancake compressor??? $150 and you're done.
For automotive work????
I don't think so.
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Old 05-15-2009, 08:28 AM   #25
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We have a Husky 26 gallon air compressor bought at Home Depot that runs on a 15 amp 120 volt circuit and works just fine for automotive work and even painting. Other than its size, its easily portable and can be plugged in just about anywhere which is a nice feature not having to worry about a 240 volt circuit to plug it into.
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Old 05-24-2009, 02:00 AM   #26
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Here is one simple solution that would be reasonably safe and almost fully code compliant.

Put a plug directly on the air compressor cord that matches the dryer outlet (NEMA 10-30).

The 30 amp breaker is fine for a DEDICATED motor circuit (even with a 12 or 14 gauge segment) and with only the compressor plugged in it meets the requirements of a dedicated "motor" circuit.

If the dryer outlet is wired to meet code the wire from the L shaped prong goes directly to the Neutral/Ground bus in the Service Panel. This has been required since 3 wire dryer circuits were introduced in the 1953 code!

The only imperfection is the Plug/Outlet (NEMA 10-30 configuration) considers the L shaped prong a Neutral that is also used for Grounding not a true Grounding terminal.

Note, any extension cord used with the compressor would also require 30 amp connectors. Any 20 amp connectors would disqualify the 30 amp breaker even for a "motor" circuit.

Putting the dryer on some sort of wheels/dolly would make the connecting easier.
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Old 05-24-2009, 03:20 AM   #27
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Quote:
Originally Posted by Jim66 View Post
Here is one simple solution that would be reasonably safe and almost fully code compliant.

Put a plug directly on the air compressor cord that matches the dryer outlet (NEMA 10-30).

The 30 amp breaker is fine for a DEDICATED motor circuit (even with a 12 or 14 gauge segment) and with only the compressor plugged in it meets the requirements of a dedicated "motor" circuit.

If the dryer outlet is wired to meet code the wire from the L shaped prong goes directly to the Neutral/Ground bus in the Service Panel. This has been required since 3 wire dryer circuits were introduced in the 1953 code!

The only imperfection is the Plug/Outlet (NEMA 10-30 configuration) considers the L shaped prong a Neutral that is also used for Grounding not a true Grounding terminal.

Note, any extension cord used with the compressor would also require 30 amp connectors. Any 20 amp connectors would disqualify the 30 amp breaker even for a "motor" circuit.

Putting the dryer on some sort of wheels/dolly would make the connecting easier.

Jim66 .,
Did you read closer to this topic ? the OP is on rental propety and the OP can not make any modifactions to the wiring system.

And the other issue is I do not know how big the compressor motour the OP have and also some of the compressor motor do not have any thermal overload switch in there { belive me I did see it more than once }.

For the rest of the answer just look what other members here allready reply in nice way that is the answer there.

Merci,Marc
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Old 05-24-2009, 04:26 AM   #28
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Marc,

I read the entire thread.

Did you read my post?

I did not suggest any change to the wiring of the rental property!

The OP says that the compressor is big enough to need 240V and small enough to run on 20 amp circuit. If it lacks motor protection, then the motor will likely burn out someday regardless of how it is used.

I offered an informed solution, I certainly welcome any thoughts regarding the validity of my suggestion.

The fact that many others have pointed out that the OP's original plan is dangerous and should not be attempted has nothing to do with what I posted.

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