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Guideline – Demonstrating Prior Use v4
Page 20 of 30
ID
Component
Description
Function
Failure Mode Sub-system Effects
Detection Method
Detected
Failure
Rate
FTD/FTS
Mitigation
1 Interface relay
Provides shutdown
function to MCC
Fail to respond
(Coil open
Circuit)
Open circuit is the
shutdown condition for
the MCC
Hardwired logic circuit
Immediate
0.0002
FTS
All connected devices will be
driven to safe state. Proof Test
shall also identify failed relay.
2 Interface relay
Provides shutdown
function to MCC
Fail to respond
(Coil Short
Circuit)
Coil Short Circuit will
de-energise the
contacts, which is the
shutdown state for the
MCC
Hardwired logic circuit
Immediate
0.0002
FTS
All connected devices will be
driven to safe state. Proof Test
shall also identify failed relay
.
3 Interface relay
Provides shutdown
function to MCC
Contacts failed
open circuit
Open circuit is the
shutdown condition for
the MCC
Hardwired logic circuit
Immediate
0.00003
FTS
All connected devices will be
driven to safe state. Proof Test
shall also identify failed relay.
4 Interface relay
Provides shutdown
function to MCC
Contacts failed
short circuit
None
None
Latent
0.00001
FTD
Proof Test is required to identify
failed relay
.
Table 2 – Example Failure Modes Analysis