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FN verification test. Current time characteristic curve

This test is applied to check the protection by automatic magneto-thermal switches or automatic differential switches under abnormal operation conditions of the installation.

Test methods

The test methodology is based on verifying the characteristic curve that the MTCB (Magneto-thermal Circuit Breaker ) and DAS (Differential Automatic Switches ) are configured with from the factory, and which includes the following actions:

  • Thermal zone curve (Joule effect) on which circuit protection against overloads is based, since excessive current for a certain length of time produces a thermal gradient that affects a bimetallic strip fitted in the switch. When the gradient exceeds a set value for a given time, this strip causes the switch to open.
  • Thermal zone curve (Ampère’s Law) on which protection of the installation against short-circuits is based, defined by very high currents in respect of the dimension of the installation for a short period of time. In this case the actuator is an electro-magnet.

To perform the test, a series of currents at magnitudes that simulate and overload or short-circuit are injected into the tested device so that the time the circuit takes to open can be measured (trip time).