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That is an old, three wire dryer cord. It does not have a ground, but instead is two hots (the two outer wires, and the \ & / on the plug end) and a neutral (center wire, L shaped on the plug end).
New circuits using the corresponding recepticals have not been allowed in the USA since sometime in the 1980's (new dryer circuits are required to be a four wire, giving them separate neutral and ground wires).
Thanks for the info. I need a 3 prong plug. I have a compressor that has a 14 amp motor. I have a 3 prong outlet in the garage that this plug fits. Can I use this cable substituting the neutral for ground?
However, your local AHJ (authority having jurisdiction, aka, electrical inspector) MIGHT allow it IF the circuit comes off the MAIN electrical panel (ie, not a subpanel). If you're talking a detached garage, you most likely have a subpanel.
If this is fed from a subpanel, you'll need to investigate the circuit further (insert standard "qualified electrician" disclaimer here).
Before going further, let me ask this: is this circuit also used for a dryer and/or somewhere someone in the future might use it for a dryer?
I am going to say no. Change the receptacle and get a cord that is the proper mate. If you have any metal on your compressor you MUST extend the bonding conductor(ground) to the unit. protect life first the worry about economics. Remember the next guy will not know what you have done if that is the case.
Is the compressor 230V? if so it likely has no Neutral wire, and all current flows from one hot to the other.
That 3 wire circuit is a NEMA 10-30, look up the wiring diagram. (L is Neutral as it is a 125/230, which we see written on the recepicle)
Options:
------------------------
Use 'L' as GND
or switch to 4 prong (does the branch wiring even have a white/Neutral? If no, no point in this option)
or hardware the compressor (I would do this)
Something seems off here: If that motor is 6hp like that picture is showing, it's gonna be more than 14a at 220v. Or was that 6hp I see in that picture on a different device?
Thats a NEMA 6-50p plug on the compressor right now, indicating the prior owner had it plugged into a 50 amp receptical (which, by code, would be freed by a 40 or 50 amp breaker). (FWIW, that plug appears to be convertible to a NEMA 6-30p by simply disassembling and changing the two hot legs from vertical to horizontal).
It's kind of weird that it says 6hp, yet uses only 14a at 220v. The motor must really be around 2hp or so. 6hp is probably some hypothetical max burst HP.
You could probably safely run this on a 20amp 220v breaker (and with the plate specifying 12g wire for an extension cord, it seems that's the manufacturers intent). I can only assume that receptical is fed by a 30a breaker. Any chance you have a manual for that thing? It would be best to defer to what the manufacturer specifies for overcurrent protection. My guess is that a 30a breaker is ok so long as the circuit was properly installed with10a wire.
It seems your original plan to use the L as ground would work, and will prevent the need to modify the circuit, so long as it is 100% clear that the circuit does not feed from a sub panel (ground and neutral are bonded together at a main panel, but not at a sub, so electrically they are basically equivalent when served from the main panel only).
If you did decide to hardwire as others suggest, you'd still need a means of disconnection within view of the compressor. To me, being able to unplug it is more straightforward.
Do note that if you modify the circuit, it would be illegal to ever put it back like it is currently. Three wire dryer circuits are allowed to remain as is so long as they are not modified.
There are 746 watts per horsepower. 3360 / 746 = 4.5 horsepower.
So the rated horsepower of 6 is in the ballpark. Manufacturers typically throw in a phoney "peak horsepower" number as a sales device and they are using 240 volts instead of 220. You will get 220 or something less.
In this situation to call the electrician seems to me more safe. I hope that all advices from this thread were helpful for you and you figured out how to resolve your issue. I noticed that you received a lot of help, that is great. Last summer when I had problems with the sockets in my apartment I tried to fix all by myself, I asked for some advices at the forum. But in the end I just called an electrician from Bates Electric Minneapolis and he fixed everything in an two hours and it was not that expensive as I thought it could be.
