Calculation formula for starting time of prepaid meter

Publish Time: 2026-04-24 09:30:08 Author: Site Editor Visit: 14

According to IEC standard, the starting calculation formula for an prepaid meter is given as t=(3600 × 1)/(C × P). What do these letters mean? T: Starting time (seconds), which is the time it takes for the meter to record the amount of electricity from being powered on. C: Meter constant (imp/kWh), which is the small red light flashing on your meter. Each time it flashes, it represents how much electricity is used. P: Starting power (kW), which is usually "starting current x voltage". In other words, this formula is used to calculate how long it takes for the meter to start reading when a particularly small current (such as 0.4% Ib) is applied. Why is there a 3600 in the formula? Because 1 hour equals 3600 seconds. The constant C of the electric meter refers to "how many flashes per kilowatt hour of electricity used", which can be converted to "how many flashes per second", and then reversed to calculate "how many seconds it takes to flash" - that is, the start-up time.
For example, you will understand: there is an electric meter with a constant C=1000 imp/kWh (which means it will flash 1000 times per kilowatt hour). Voltage 220V, basic current 5A (which is 5 in the 5 (60) A marked on your home meter), level 1 prepaid meter.
According to IEC standards, the starting current of a Class 1 meter is 0.4% Ib, which means that 0.4% x 5A=0.02A (20mA)
Step 1: Calculate the starting power according to Ohm's law power calculation formula. Power=voltage x current 220V x 0.02A=4.4W, converted to kilowatts: 4.4W=0.0044kW
Step 2: Use the formula to calculate the time C × P=1000 × 0.0044=4.4t=3600 ÷ 4.4 ≈ 818 seconds Step 3: Change to easy to understand units, 818 seconds ÷ 60 ≈ 13 minutes and 38 seconds
That is to say, if a current as small as 20mA is applied to this meter, it needs to be able to run a single word within 13 minutes and 38 seconds (flashing the meter to record a pulse) to be considered qualified for startup.

The above refers to a single-phase meter. What about the three-phase meter? A three-phase meter has three live wires, and each phase has current, so the total power needs to be calculated by adding up the three phases: P=3 × 220V × 0.02A=13.2W=0.0132kW. Another formula is: t=3600 ÷ (1000 × 0.0132) ≈ 272.7 seconds, which means that if the three-phase energy meter can record one pulse within 4 minutes and 33 seconds, the startup test is judged to be qualified. Did you see that? With the same starting current of 0.02A, a three-phase meter can read in just over 4 minutes, which is much faster than a single-phase meter's 13 minutes - because the total power of the three phases combined is large and powerful.

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