Product Overview 1-17
The following table defines the SMC-Flex PTC thermistor input and
response ratings:
Table 1.A PTC Input Ratings
The following figure illustrates the required PTC sensor
characteristics, per IEC-34-11-2.
Figure 1.18 PTC Sensor Characteristics per IEC-34-11-2
PTC Trip
The SMC-Flex will trip with a PTC indication if:
• No other fault currently exists
• PTC protection is enabled
• The resistance across terminals 23 and 24 is either greater than
the relay’s response resistance or less than the short-circuit trip
resistance.
Excessive Starts/Hour
The SMC-Flex controller allows the user to program the allowed
number of starts per hour (up to 99). This helps eliminate motor stress
caused by repeated starting over a short time period.
Response resistance 3400 Ω ±150 Ω
Reset resistance 1600 Ω ±100 Ω
Short-circuit Trip Resistance 25 Ω ±10 Ω
Maximum Voltage at PTC Terminals (R
PTC
= 4kΩ) < 7.5V
Maximum Voltage at PTC Terminals (R
PTC
= open) 30V
Maximum Number of Sensors 6
Maximum Cold Resistance of PTC Sensor Chain 1500 Ω
Response Time 800 ms
10
20
100
250
550
1330
4000
-20°C TNF-20K
0°C TNF- 5K
TNF+15K
TNF+ 5K
TNF
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