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DON'T USE YOUR FILTER AS THE FUSE

Posted by Holger Urban

How to select the right fuse / MCB to work with your filter

In electronic equipment the focus often lies on the operational demand current (amperage) of a system. Therefore, modern systems are partitioned into different branches. Those branch circuits can feature over current protection devices. If a problem occurs on the feeder or branch level a fault needs to be identified and the system needs to fail safely. Failing safely not destructively means that all devices not considered as protection devices, including an EMC Filter, need to survive and be in accordance to the overcurrent protection.

Available MCBs (Miniature Circuit Breakers) according to standard IEC60947-2 feature current ranges from 1A to 63A and are tripping according to certain ranges. EMC filters are designed to match overcurrent protection devices (thermally) and are designed to handle over current situations for a limited amount of time.  Certainly, there are huge differences between a fuse and a MCB but considering the diagram of tripping (time to current), a proper filter can easily be determined.

Tripping characteristics of MCBs based on application:
 
IEC 60898-1 overcurrent protection for cables: B, C and D
IEC 60947-2 protecting motors, transformers and cables: K
 Protecting control circuits with high impedances, voltage converter circuits: Z

 

Overall it needs to be understood that the circuit protection device protects the filter against overcurrent. So, let your MCB trip not your filter.

NOTE: Filter needs to be placed downstream of the protection device.

Schaffner considers a calculated approach based on experience to evaluate the overload capability of any filter. Schaffner filters can be used with MCBs of class B, furthermore the filter can be verified with additional tests and certifications for special needs. Normalized to multiples of rated currents the filter overload capability compared to the double logarithmic scale of tripping MCB is displayed below. In addition, the general overload capability of our filters is displayed.

NOTE: Characteristics may vary in real application. Local installation guideline may apply

 

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Picture 1: Filter compares to MCB type B 

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Picture 2: Overload of a 40°C rated filter (100°C max)

Please contact our local sales office to find out how to shape electrical power with the selection of filter.

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