What is the safest way to test an outlet?
In many cases, a homeowner may think an outlet is not working when it is in fact still transmitting power. For this reason, it's important to be cautious whenever testing an outlet and not assume that there is no danger. Instead of using a small appliance for testing, you should use an outlet tester. An outlet tester is created specifically for this purpose, and is available from any home improvement store. The outlet tester has plugs so it can be inserted directly into an outlet, and several lights along one side. The lights flash in specific patterns to tell you whether the outlet has power, if the wire is grounded and other information about the wiring. Using the legend that comes with the guide, you can read the pattern of lights and determine the exact status of the outlet. Another good tool for testing an outlet is a voltage detector. A voltage detector makes noise to indicate the electric current being present in the outlet. However, it does not offer as much information as the outlet tester does.
If you have any reason to believe the outlet is unsafe, the best way to proceed is to allow a professional electrician test it. If the outlet has brown or black singe marks, makes a popping or crackling noise or keeps tripping when you try to use it, call a professional instead of trying to test it yourself.