Siemens UL 1066 Operating Instructions Manual page 162

Testing LEDs only
Pushing the "Test" button several times with pauses in between switches the LEDs on successively. After the last LED, all LEDs are
switched on.
Repeated pushing the "TEST" button starts the test mode again, and all LEDs, inputs and outputs are switched off.
Quitting the test mode
Do not press the "TEST" button for approximately 30 sec.
If all LEDs are on, the test mode will already be quitted after about 4 sec.
9.2.3.2 ZSI module
Function
When circuit breakers are combined with ZSI modules, a short-circuit occurring in systems with several grading levels can be precisely
localized.
For this purpose, all circuit breakers are interconnected via their ZSI modules.
When a short-circuit or ground-fault occurs, each circuit breaker affected by the short-circuit current queries its downstream circuit breaker
to determine whether the short-circuit is present in the next downstream device. Only the circuit breaker nearest the short-circuit, in the
upstream direction, is tripped. If "S" or "S+G" is selected on the ZSI module and the circuit breaker does not receive a blocking signal -
ZSI-IN - from its downstream circuit breaker, in the event of short-circuit, the delay time setting for the short-circuit trip is set to 50 ms. If a
short-circuit is detected, a blocking signal - ZSI-OUT - will be sent to the upstream circuit breakers. The trip takes place after 50 ms. It 
typically delays between 80 and 90 ms.
If "S" or "S+G" is selected on the ZSI module and the circuit breaker does not receive a blocking signal - ZSI-IN - from its downstream circuit
breaker, in the event of ground-fault, the delay time setting for the ground-fault trip is set to 100 ms.
If a ground-fault is detected, a blocking signal - ZSI-OUT - will be sent to the upstream circuit breakers. The trip takes place after 100 ms. 
It typically delays between 130 and 140 ms.
After a maximum delay time of 3 s, a given blocking signal ZSI-OUT is terminated.
Installation
 (page 9-78)
Connection
 Connection setup (page 9-78)
Only one ZSI module can be connected per circuit breaker.
If the ZSI module is used together with other cmodules, the ZSI module must be connected directly to the COM15 module or
hand plug X8.
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