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First we take a look at the IEC standards.
The run-time depends on several factors like
- accuracy class
- meter constant
- number of elements
- Nominal Voltage
- Maximum Current
When the voltage is applied with no current flowing in the current circuit, the test output of the meter shall not produce more than one pulse.
For this test, the current circuit shall be open-circuit and a voltage of 115 % of the reference voltage shall be applied to the voltage circuits.
|Minimum Required Time for No-Load Test|
|IEC62053-21 class 2||IEC62053-23 class 2|
|IEC62053-21 class 1||IEC62053-22 class 0.5S|
|IEC62053-22 class 0.2S|
For MID meters according to DIN EN BS 50470-3 the calculation formula is different.
|Minimum Required Time for No-Load Test EN50470-3|
|Direct connected class A|
|Direct connected class B|
|Direct connected class C|
|CT connected class A|
|CT connected class B|
|CT connected class C|