**where:**

**Rr =**

**register ratio found on front plate, back plate, or frame of**

**register**

**Kh = watthour constant**

**TF = transformer factor = CT ratio x PT ratio**

**Gr =**

**first gear reduction ratio usually 50 or 100 (obtain from**

**manufacturer)**

**Self-contained meters, used for domestic service and small industry, usually**

**have a multiplier of either 1, in which case no multiplier would be shown, or**

**10. Whenever the multiplier is more than 1, the words "multiply by", followed**

**by a number appear on the front plate. For transformer-rated meters, which**

**are used with instrument transformers for heavy industrial and central station**

**metering, the multiplier can be 10, 100, 1,000, 10,000, etc. In this case the**

**register is supplied for only one transformer factor. The multiplier can also**

**be numerically equal to the transformer factor. If so the register will read**

**in terms of secondary energy and be read on a "secondary-reading register*'.**

**In any watthour meter, the total energy in kWh is equal to the product of the**

**watthour constant (Kh) and the disk revolutions divided by 1,000:**

**Kh x disk revolutions counted**

**kWh =**

**1,000**

**To determine total energy in kilowatt hours as counted by a transformer-rated**

**meter, the secondary reading register would be multiplied by the ratio of the**

**instrument transformers which is called the transformer factor. In a system**

**using current transformers with a rated primary current of 20 amperes, total**
**energy registered would equal:**

**Kh x disk revolutions 20**

**x**

**=**

**kWh**

**5**

**1,000**

**If the system also contained a PT with a 7,200 to 120 ratio, the total energy**

**registered would equal:**

**Kh x disk revolutions 20 7,200**

**x**

**x**

**kWh =**

**1,000**

**5**

**120**

**In this example, the numbers 4 (20/5) and 60 (7,200/120) are the ratios of CT**

**and PT respectively. Their product, 240 (4 x 60), is the transformer factor**

**for this meter. Whatever value is shown on the secondary register must be**

**multiplied by the transformer ratio to obtain the correct number of kWh used**
**in the primary circuit.**

**2.1.6.3 Voltage Rating.**

**Meters are available for 120-, 240, or 480-volt**

**service as required.**

**9-16**