Siemens UL 489 Operating Instructions Manual page 112

Protective function has tripped
(overcurrent)
- Indicator lights up when the Query
button is pressed
- Only one trip cause is displayed
- Only the last trip cause is 
displayed
LED T.U. ERROR
1. T.U. Error flashes:
Limited protective function, the protective
parameters are reset to minimum values.
Causes:
- Rated current of the Rating Plug is higher
than that of the circuit breaker
- Rotary coding switch in undefined
intermediate position
- Trip unit defective
2. T.U. Error lights up continuously:
Protective function not available.
Causes:
- Rating Plug not compatible with 
circuit breaker type
- Trip unit defective
9 – 10
or