Isn't a ground for the compressor NEMA 6-20P plug the same as the neutral for the dryer NEMA 10-30R receptacle?
Actually, I should have mentioned, there is no sharing. There is no dryer on this spare receptacle in the garage. The dryer is on a separate NEMA
10-30R in the house. I do agree that unplugging a dryer once every six months to use the compressor would be a pain.Elmo wrote: ...
Assuming the adapter is compliant it isn't...
The compressor motor will have it's own overload protection.
That's all the circuit breakers protect against for anything plugged into them; there's no difference in the case of the dryer being plugged into the outlet as the compressor; the internal dryer motor isn't a 30A device by any stretch, either.
Correct, and in fact w/ the compressor being a 240V load only, there is no need for and no neutral current. The shared conductor is serving only the ground function at that time, just as would the third conductor in a 20A plug connection.
No...the others are simply incorrect in understanding of Code and perhaps even function of three-wire dryer circuit...
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I wondered about that. Does the "code" cover temperary adapters?
Doesn't the code only apply to the wiring in the walls?
This is an adapter, which is not permanently connected.
And, the wiring is the same, either way, as far as I can tell. The only ground/neutral difference I see is the NEMA 6-20P ground for the compressor is connected to the NEMA 10-30R ground/neutral for the dryer. But isn't that dryer neutral connected directly to ground anyway at the panel on the other side of the wall?
And, the 20-amp rating for the compressor is connected to a 30-amp breaker instead of a 20-amp breaker. But, that will still protect the wiring in the wall from 30 amp surges (it just won't protect the compressor).
Right?
"Elmo" wrote>
But I bet they cheapened it and now is made in China, or at least major parts of it
It was my fault for not explaining clearly.
The plug on the compressor is a NEMA 6-20P (not a NEMA 5-20P); but I do agree that's a great point to doublecheck.
The motor will marked as dual-voltage if it can...wouldn't be too surprising but I'd stick w/ 240V as you'll need double the amps for 110V and you may well be in worse conundrum of not having a circuit w/ the ampacity to run it on 120V...
There's that turning around of the actual situation on a dryer outlet wiring again for one and the misconception regarding the point of 30A circuit protection having anything to do w/ the load plugged into the outlet. Both are simply wrong.
The third conductor is _NOT_ the neutral serving as ground, it is THE_GROUND_CONDUCTOR_ sharing service as the neutral for the 120V components in the dryer (motor/lights/timer/etc.).
For the other, the 30A breaker is there to protect the circuit wiring; it is the responsibility of the load to have the correct protection for itself internally.
For the 240V components (the heater elements) of the dryer, yes; identically. There is no 120V load on the compressor so the need for the sharing of ground/neutral disappears and is, therefore, fully compliant with current NEC for 240V loads whereas the dryer would require a four-wire connection to be compliant to current NEC. From that standpoint, the compressor is "more correct" than the intended use of the dryer on the circuit (that _was_ compliant w/ NEC of the time, of course).
Again, if the adapter you're using is compliant and well made, ignore the do-gooders' advice here--they mean well but are simply misinformed or overly cautious or just don't understand (or maybe even all of the above :) ).
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If that's the case, why don't you just replace the breaker and receptacle with a 20 amp
:)
I do appreciate the double check (as that's what this thread is all about!).
Check twice, plug in once! :)
You show what appears to be a NEMA 5-20P; I have the NEMA 6-20P. The difference is (looking at the plug head on with the ground up), my sidewise blade is on the right whereas that plug's sidewise blade is on the left.
BTW, the plate on the wheeled tank says: Sears Craftsman model 919.176940 240 volts 15 amps
It's a ground that shares neutral function, not vice versa...
Yes, addressed elsewhere...
In that case, the simple (and relatively inexpensive) solution would be to swap to a 20A breaker to support the proper 20A outlet style to plug the compressor in directly. There's nothing wrong w/ the wiring being _larger_ than required for the ampacity of the circuit; all it does is mean there will be even less voltage drop than otherwise would be.
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Your chart has little W's and G's and "X" and "Y" for the hot black wires.
I presume the "w" stands for white, does it not?
I just googled my 30-year-old Sears Craftsman model 919.176940 and, as expected, couldn't find it for sale new anymore to check the prices.
But, used, it's 60 bucks!
It looks like I can still get parts for it at
But no manual for the 20-gallon 125psi air compressor seems to exist on the net.
Elmo wrote: ...
As noted elsewhere, you'd be better served to go to 20A breaker/plug and junk the adapter, though...
Strictly speaking, it's "neutral"; but conventional (USA, anyway) wiring is white for neutral, yes.
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yes, that's correct
You seem to understand the situation the best.
The adapter is a standard metal box with the NEMA-6-20R and a three-inch long strain relief for the dryer cord securely attached to the metal box.
The only problem I had was the dryer cord had three brass "circles" as the connection point but the NEMA-6-20R had screws which didn't expect to be taken out to accomodate circular connections. The last few threads removing the screws "broke" something, as the screws are clearly designed to stay in.
When I removed the three screws (two brass for the black wires and one green-painted steel for the ground/neutral wire), it was hard to get them back in.
I wondered if it was the male screw or the female hole that "stripped" when these type of stay-in screws are removed. I guessed it was the female part that stripped, so I cleaned it up with an 8x20 tap and guess what.
The screws went right in.
The DESIGN of these things is amazing. What is the reason for the screws being designed not to come all the way out. And, did I compromise something by cleaning up whatever it was that strips when you do remove the screws?
Very well stated!
Not true at all. In fact the code required that this 3d wire be insulated and white. That is why it usually got run in 10-3 romex. There was an exception that allowed SE cable with a bare ground.
In part 250.60 (1993 the last cycle this was legal to install) says "except for mobile homes and recreational vehicles, shall be permitted to be grounded to the grounded circuit conductor"
The "grounded" conductor is the neutral.
Elmo wrote: ...
a) So they don't get lost???? :)
b) No.
At manufacture the screws are inserted then deformed on the ends to prevent accidentally backing them out fully. The plugs aren't designed for other than wire loop around the screw so there's normally no need to remove them so it's a convenience to have the resistance. Since you had the ring terminals, what you did is fine.
I'd still suggest consideration of the conversion to a 20A circuit for a permanent solution, however, altho I'll agree the solution is safe and electrically compliant w/ Code intention.
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I agree. If this is an"extra" dryer outlet in the garage I'd take consider switching it. A 20 amp breaker is only about $10. Another $10 would get you a metal box and proper 20amp outlet. The wire is already there. If it doesn't have a ground you could use the neutral as long as you mark it as ground.
Jesus Christ, with all this advice you will be lucky if you don't burn the house down and put the lights out in the whole neighborhood. Just go to Home Depot and get a receptacle that fits the plug. Turn off the breakers and remove the old 30 amp receptacle and install the new 20 amp one. The "hot" wires go on the outside screws they should be colored and the ground/neutral on the middle one white if it was done correctly, might be bare if someone took a short cut. Flip the breakers back on and there should be 115 volts between each of the outside holes to neutral/ground holes and 220 volts from outside hole to outside hole. Plug the thing in and turn it on and get that basket ball aired up. Working air compressors are just real handy to have around, I use mine for lots of things, great for blowing out a dusty old computer, adjusting the pressure in the car tires, gobs of uses.
Here's the summary after reading all the posts, especially djb's (Dave Bot..o perhaps?) posts.
In summary, it appears, as long as my adapter is well made (picture of it below), it's safe (even safer than plugging in a dryer) to plug in the cord that I made.
A picture of the adapter cord and compressor is here:
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