People are aware of this, but the regular sockets are connected to 120V only. You can (easily) hack an electrical circuit ("consumer unit" in UK) to deliver 240V on an existing plug, but that would be a very serious code violation. SO unless you hack your house circuits, you have 120V on regular sockets.
You can replace the receptacles with ones meant for 240VAC at the same time you modify the wiring. Then it should be okay. Replacing the NEMA 5-15 receptacles with NEMA 6-15 receptacles would work.
