34   Maintenance and fault tracing
The person responsible for the design of the complete safety function should also note the 
Recommendation of Use CNB/M/11.050 published by the European co-ordination of 
Notified Bodies concerning dual-channel safety-related systems with electromechanical 
outputs:
• When the safety integrity requirement for the safety function is SIL 3 or PL e (cat. 3 or 
4), the proof test for the function must be performed at least every month.
• When the safety integrity requirement for the safety function is SIL 2 (HFT = 1) or PL d 
(cat. 3), the proof test for the function must be performed at least every 12 months.
This is a recommendation and depends on the required (not achieved) SIL/PL. For 
example, safety relays, contactor relays, emergency stop buttons, switches etc. are 
typically safety devices which contain electromechanical outputs. The STO circuit of the 
inverter unit does not contain any electromechanical components.
 Competence
The maintenance and proof test activities of the safety function must be carried out by a 
competent person with adequate expertise and knowledge of the safety function as well as 
functional safety, as required by IEC 61508-1 clause 6.
Fault tracing
 Warning messages generated by the drive
 Fault messages generated by the drive
Any failures of the Safe torque off function must be reported to ABB.
Warning Cause What to do
START INHIBI Safe torque off function has been 
activated while the drive was stopped.
Close Safe torque off function switch. If the 
switch is closed and the warning is still 
active, check power supply at ASTO board 
input terminals. Replace ASTO board.
Fault Cause What to do
GD 
DISABLED X
ASTO board power supply of parallel-
connected R8i inverter module has been 
switched off during run. X (1…12) refers 
to inverter module number.
Check Safe torque off function circuit of this 
module (X).
Replace ASTO board of R8i inverter 
module.
START INHIBI Safe torque off has been activated during 
motor run or motor start command has 
been given when Safe torque off is 
active.
Close Safe torque off function switch. If the 
switch is closed and the fault is still active, 
check power supply at ASTO board input 
terminals. Replace ASTO board.