I agree with ameterguy. Ideally, a network meter is used for the described service, but there is a possibly less costly option that is also intended for the application.

Look at www.hialeahmeter.com/self.htm for a (remanufactured/tested) 120V form-12 class-100 or -200 meter. A 5-jaw socket is needed.

Another source is Austin International at www.electricalconnector.com/Remanufactured%20Meters%20Brochure.pdf