Power outlets in North American homes generally supply 110 volts, but some provide 220~240 volts. The plug for your electric oven and clothing dryer may look different from your average electrical socket, that is because they supply more voltage than the regular socket, 220 volts. Plugging in an appliance that does not match the outlet could damage both the outlet and appliance. Testing the voltage of an unknown socket is important to avoid damage and injury.
Turn the dial or select the button on the multimeter so that the meter measures voltage in an A/C circuit. This selection should be labeled with a V with a wavy sine wave over the letter.
Insert the metal tip of the test lead at the end of the black wire into one of the two terminals in the 240V socket.
Insert the other metal tip of the test lead at the end of the red wire into the other remaining socket in the power outlet.
Read the display screen to determine the voltage present. If it reads between 215 to 245 volts, the outlet works properly and powers appliances with this voltage range.