Monitoring Relays

Monitoring relays are a type of relay that trips a circuit breaker when a fault is detected. A relay is an electrically controlled switch that is used to turn the power on or off in a circuit.


Monitoring relays are more sophisticated than regular relays, as they have adjustable operating conditions, whereas normal relays switch according to a fixed threshold. They measure a given parameter, such as voltage or temperature, and will trip a circuit breaker when the parameter gets too high or low.


What are monitoring relays used for?


Monitoring relays have a wide range of uses, depending largely on the factor being monitored. For example, they can protect against overcurrent if measuring current, or they can detect an abnormally low frequency if frequency is being measured.


Types of monitoring relay


The main way in which monitoring relays differ is the function that they measure. This can be a number of things, including: voltage, current, temperature and frequency.


The factor that you need to measure will decide which monitoring relay you choose.


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Description Price Monitoring Application Supply Voltage Contact Configuration Voltage Sensitivity Electrical Phase Voltage Sensing Range Current Sensitivity Minimum Current Sensed Maximum Current Sensed Phase Sensitivity Time Delay Temperature Sensitivity Temperature Sensing Range Frequency Sensing Range
RS Stock No. 794-3957
Mfr. Part No.MJ83BK
BrandGIC
£45.42
Each
Units
Thermistor 110 → 240 V ac DPDT - 1 - - - 6A - 100 ms, 500 ms - - -
RS Stock No. 518-7051
Mfr. Part No.3UG4614-1BR20
BrandSiemens
£108.70
Each
Units
Phase, Voltage 160 → 690 V ac DPDT Undervoltage 3 160 → 690 V ac - - - Phase Failure, Phase Imbalance, Phase Sequence 0.1 → 20 s - - -
RS Stock No. 775-7895
Mfr. Part No.1SVR730794R3300
BrandABB
£181.15
Each
Units
Phase, Voltage 300 → 500 V ac DPDT Overvoltage, Undervoltage 3 300 → 500 V ac - - - Phase Failure, Phase Sequence 0.1 → 30 s, 0 s - - 45 → 65 Hz
RS Stock No. 261-909
Mfr. Part No.84873021
BrandCrouzet
£72.26
Each
Units
Phase 208 → 440 V ac DPDT - 3 - - - - Phase Failure, Phase Sequence 500 ms - - -
RS Stock No. 794-3951
Mfr. Part No.MJ93BK
BrandGIC
£45.50
Each
Units
Thermistor 220 → 440 V ac DPDT - 3 - - - 6A - 100 ms, 500 ms - - -
RS Stock No. 291-3144
Mfr. Part No.IL9077.12 3/NAC 400/230V 0.1-20S
BrandDold
£173.49
Each
Units
Voltage 230/400 V ac DPDT Overvoltage, Undervoltage 3 - - - - - 0.1 → 20 s - - -
RS Stock No. 146-092
Mfr. Part No.RM17JC00MW
£90.00
Each
Units
Current 24 → 240 V ac/dc SPDT - - - Overcurrent 2A 20A - 0.5 s - - -
RS Stock No. 746-6025
Mfr. Part No.3RN1010-1CG00
BrandSiemens
£63.63
Each
Units
Thermistor motor protection relay 110 V ac SPDT - - - - - - - - Winding Temperature +60 → +180°C -
RS Stock No. 614-9397
Mfr. Part No.84871130
BrandCrouzet
£103.02
Each
Units
Current 24 → 240 V ac/dc DPDT - 3 - Overcurrent, Undercurrent 0.1A 10A - 0.1 → 3 s - - -
RS Stock No. 609-8075
Mfr. Part No.LT3SM00ED
£336.00
Each
Units
Temperature 24 → 48 V dc SPDT - - - - - - - - Overtemperature, Undertemperature - -
RS Stock No. 850-5360
Mfr. Part No.LXPRC/S 400V
£65.93
Each
Units
Phase, Voltage 400 V ac SPDT Overvoltage, Undervoltage - 300 → 380 (Under) V, 420 → 500 (Over) V - - - Phase Failure, Phase Sequence 0.2 → 10 s - - -
RS Stock No. 518-7203
Mfr. Part No.3RN1011-1BB00
BrandSiemens
£85.50
Each
Units
Thermistor motor protection relay 24 V ac/dc DPDT - - - - - - - - Overtemperature, Undertemperature +60 → +180°C -
RS Stock No. 518-7275
Mfr. Part No.3UG4511-1BP20
BrandSiemens
£76.22
Each
Units
Phase 320 → 500 V ac DPDT - 3 - - - - Phase Sequence - - - -
RS Stock No. 240-9320
Mfr. Part No.BA9053/410 AC1A/5A/10A AC230V 0-20S
BrandDold
£170.62
Each
Units
Current 230 V ac SPDT - - - - 0.1A 10A - 0.5 → 5 s - - -
RS Stock No. 442-9455
Mfr. Part No.1SVR550881R9400
BrandABB
£59.93
Each
Units
Phase 220 → 240 V ac, 380 → 440 V ac SPST - 1, 3 - - - - NEUTRAL 150 ms - - -
RS Stock No. 321-6826
Mfr. Part No.45200 110VAC
£63.55
Each
Units
Temperature 110 V ac SPDT - - - - - - - 50 ms Overtemperature - -
RS Stock No. 775-7902
Mfr. Part No.1SVR730884R3300
BrandABB
£184.28
Each
Units
Phase, Voltage 300 → 500 V ac DPDT Overvoltage, Undervoltage 3 300 → 500 V ac - - - Phase Failure, Phase Imbalance, Phase Sequence 0.1 → 30 s, 0 s - - 45 → 65 Hz
RS Stock No. 397-9145
Mfr. Part No.70POCR 400VAC
£151.97
Each
Units
Current 400 V ac DPDT - 3 - Overcurrent - 5A - 0.2 → 10 s - - -
RS Stock No. 819-3248
Mfr. Part No.K8AK-LS1 24VAC/DC
BrandOmron
£50.95
Each
Units
Level Control 24 V ac/dc SPDT - - - - - - - - - - -
RS Stock No. 146-070
Mfr. Part No.RM35S0MW
£143.00
Each
Units
Speed 24 → 240 V ac/dc SPDT - - - - - - - 0.6 → 60 s - - -
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