Zone-selective interlocking ZSI


The microprocessor-controlled, zone-selective interlocking function ZSI has been developed in order to control the total breaking time in low-voltage networks with multiple molded case circuit breakers connected in series.

Advantage of ZSI:

Regardless of the number of series-connected molded case circuit breakers, all short circuits in the network can be cleared within a maximum time period of 50 ms. Short-circuit clearance times should be minimized, particularly in the case of system short circuits of very large magnitude.


Downward compatibility

The ZSI function is downward-compatible with the ZSI function of the 3VL and 3WL series of molded case circuit breakers.


Use of the ZSI function is conditional upon the connection of a dedicated EFB300 external function box to each 3VA2 molded case circuit breaker. The EFB300 allows molded case circuit breakers to communicate with one another, a capability which is a basic requirement for the ZSI function.

To permit utilization of the ZSI function, EFB300 external function boxes must be interconnected as illustrated below: