nVent RAYCHEM Elexant 4010i/4020i User Manual
RAYCHEM-AR-H60624-40X0iOpsManual-EN-1905
nVent.com
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Type
SIL
1
Architecture
MTTR
2
(hrs)
HFT
3
SFF
4
Proof Check
Interval (years)
PFD avg.
6
4020i-Mod-
IS-LIM
SIL 2
1oo1
8
0 (1oo1)
5
98.91%
1
1.64E-05
10
1.64E-04
20
3.28E-04
Table 13- Safety Integrity Level
Safety Integrity Level
1
SIL = Safety Integrity Level
2
MTTR = Mean Time to Repair
3
HFT = Hardware Fault Tolerance
4
SFF = Safe Failure Fraction
5
1oo1 = One out of One
6
PFD = Probability of Failure on Demand
4.1.13 System Failure Modes
When using the Elexant 4020i Limiter variant in a safety critical application, it is necessary to consider
the failure mode of all elements, and the probabilities of those failures, in order to understand their
possible effect, and what mitigation may be necessary. The table below summarizes the failure modes
of this element.
Description
Failure Mode
Detected/
Undetected
Safe/
Dangerous/
No Change
1year
Probability
10 Year
Probability
25 Year
Probability
Loss of
redundancy
One of the relay outputs
is always closed.
The other output still
functions normally.
Undetected
Dangerous
3.88E-04
3.87E-03
9.65E-03
Internal signal
short
A trip is reset silently,
or without user
intervention. A forced
Trip clears on its own, or
can’t be forced.
Detected
Dangerous
3.60E-04
3.59E-03
8.96E-03
Undetected
Dangerous
4.00E-05
4.00E-04
1.00E-03
Output short
The limiter output relay
(but not the main output
override) is stuck in the
ON position regardless
of the temperature.
Detected
Dangerous
8.15E-03
7.85E-02
1.85E-01
Undetected
Dangerous
7.41E-04
7.38E-03
1.84E-02
Unreported In-
ternal Power
Diagnostic
Failure
No change to operation.
Reported power failure
has no known effect.
Undetected
No Change
1.21E-03
1.20E-02
2.97E-02
Table 14- Failure Modes
4.1.14 Response to Fault Conditions
In case a failure of the safety system is detected, either during operation or during routine maintenance
when executing a function test, the unit should be switched off and taken out of service. Defects in
the safety system cannot be repaired in the field. Defective units are to be replaced and returned to the
manufacturer for investigation. Please contact your nearest nVent representative for more instructions.
Information about the unit, including the device serial number, and limiter firmware version, may be
requested by the nVent representative. This information is available via the Info screen on the product
GUI (Section 5.3). A list of worldwide representatives can be found on
www.nVentthermal.com.