I worked for the power utility in my province in Canada. We used to set the voltage coming out of the substation or regulator at around 123V-124V. This gave a little higher voltage to the homes that were close and it dropped as it went down the line. At the end of the line we wanted to keep it above 115V-116V. So if you are close to the supply you could have 124 X 2 = 248V at the plug in. As mentioned the voltages on each leg should be within a few volts of each other so I would think 126V should be about the highest you would see. If you check across the plug and have more than 250V you might want to check with the utility to see if they can lower it for you.
Brian
