How long does a no-load test take?

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

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
nominal voltage V
maximum current A
elements
meter constant i/kWh
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
nominal voltage V
nominal current A
elements
meter constant i/kWh
Direct connected class A
Direct connected class B
Direct connected class C
CT connected class A
CT connected class B
CT connected class C
How long does a no-load test take?
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Published by

Lao Ren

more than 30 years experience in energy metering Product Director Shenzhen CLOU Electronics

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