Watt-hour Meter Basics

Before covering the basic components of the electro-mechanical watt-hour meter, it is important go over the nameplate information on the watthour meter. The nameplate includes all of the necessary information that is important for each installation. For example, look at the watthour meter below. On the bottom portion of the watthour meter, you will see amperes, cycles and so forth. So, what do these mean?

15 amperes is the number of full load amps that the watthour meter is tested at. Keep this in mind because I will be adding a section on testing later.

120 volts is the voltage class. This says that the voltage coil in the watthour meter is rated at 120 volts.

2 wire. This tells us that the meter is to be used on a 2 wire service.

Kh. The Kh of the meter is what is know as the watt-hour constant. What this means is that it takes 1.8 watts to make the disk turn one revolution.

60 cycles. This is the frequency of electricity, measured in hertz, of the power grid in the United States. There are some other countries who use 50 cycles.

Model AC1. This is just the model number that this manufacturer gave this meter.

At the bottom is the serial number. This is used to identify each meter. The serial number is tied to each customers account so we know how much to bill each customer.

Which leads to the register at the top. The register is the portion of the watthour meter that records all of the energy that has been used by the customer.

Also important is the type. This particular watthour meter happens to be an I-50s.

This is just a brief overview. There will be more to come. For more advanced information, go learn about Blondel’s Theorem and the Hall Effect.