I need to add a 240V-20A outlet for a largish window air conditioner in my home.
I have read several places that code now requires all 240V outlets to be four wire (i.e. three wire plus ground.) This doesn't make sense to me however, since if the outlet is for a device that uses only 240V (as opposed to both 120 & 240V, like a range or drier), then the neutral wire won't do anything, other than run from the panel to the outlet. The device plugged in won't even be connected to it.
I realize that it was once permissible to wire a drier with only three wires and that now four are required, and I can understand the logic for that code change, since there really should be a dedicated safety ground, but I don't understand the reasoning behind requiring a neutral wire in a
240V-only circuit. Shouldn't two hots and a ground be all that is needed, both electrically and for proper protection?
Is what I've read incorrect? Possibly just a misinterpretation of the newish requirement for split-voltage receptacles to be four wire?
It's not just on-line or in other suspect places where I've picked up this info, I've seen it in electrical books as well. For instance, Home Depot's "Wiring 1-2-3" book states in the "Adding a 240V Receptacle" chapter:
"...Recent codes require four-wire receptacles; three-wire receptacles were once acceptable."
In the very next paragraph they then seem to contradict that however, stating:
"a 20-amp, 240-volt receptacle for a window air conditioner or other appliance requires only 12/2 cable..." (and the illustration shows a standard three-slot, 240V-20A receptacle - with two hots and a ground.)
The next section of this book is "Adding a 120/240 Volt Receptacle", so it would seem that the above quotes are meant only to apply to 240V receptacles.
I'm confused. :-(
- Jeff