How long does a no-load test take?

Note: The IEC62052-11 edition 2 has introduced a new calculation formula for no-load test. This calculation is valid for meters with type test certificates issued after June 2020.

For all meters before that date the calculation below is valid.

The run-time depends on several factors like

  • accuracy class
  • meter constant
  • number of elements
  • Nominal Voltage
  • Maximum Current

Test criteria
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 IEC
Nominal voltage
Maximum current
Elements
Meter constant
IEC formula
IEC62053-21 class 2
IEC62053-23 class 2

IEC formula
IEC62053-21 class 1
IEC62053-22 class 0.5S

IEC formula
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
Nominal current
Other values from the IEC settings
EN formula
Direct connected class A
Direct connected class B
Direct connected class C
CT connected class A
CT connected class B
CT connected class C

Editor's note: This article was originally published in July 2019 and has been updated for comprehensiveness.

2 Replies to “How long does a no-load test take?”
  1. Hello Sir,
    I have an energy meter of rating mentioned
    Voltage : 3 X 58/100….277/480V – Which voltage be taken for calculation 58 or 277
    Current : 5(10)A
    Meter Constant without CT 10000 imp/kWh & CT ratio 100/5A , Meter constant 499.989 imp/kWh.
    Could you please help me to calculate the time for No load testing
    Also I would like to know the condition for Starting current testing s per the IEC 62053-22/23 & 11

    1. You have a meter with wide range voltage. If you want to do an acceptance test, you use the minimum and the maximum voltage (test twice). If the meter was already in the field and you know the usage voltage, it’s ok to test with this voltage only. Since the IEC 62052-11 has changed in 2020, you need also to know whether the meter was type-tested with the new standard.
      Let’s say, you have a new meter acc. to IEC 62052-11:2020. It’s a transformer-operated meter class 0.2S. (starting current 0.001 In). Then, using the the formula you need 25 minutes and 5 seconds.
      For the IEC starting test and other test procedures, look at a complete listing here.

Leave a Reply

Your email address will not be published. Required fields are marked *