How to Calculate Meter Factors

Calculating the multiplying factor for an electrical meter requires determining the current transformer ratio. This ratio is between the rated primary current and the rated secondary current. Understanding the ratio requires knowing either the voltages or the number of turns in the coil. The ratio implies the number of amps the secondary current produces when the corresponding amount runs through the primary. The multiplying factor for the meter is the result of the ratio. The most common secondary current is 5 amps.

A standard electric meter resembles the odometer of an automotive console.

Step 1

Determine the ratio of the primary to secondary current.

For example, a common ratio for electrical meters is 200 for the primary current and 5 for the secondary, producing a ratio of 200 to 5.

Step 2

Solve the ratio by dividing the primary current by the secondary current.

For example, 200 to 5 equals 200 / 5 or 40.

Step 3

Multiple the resulting number (in this case 40) by any differences in the reading during different times to calculate actual power consumption. The result of the ratio is the multiplying factor for the meter.

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