RCM420-D-2 BENDER

The AC and pulsed DC sensitive residual current monitor RCM420-D (Type A) from Bender is 

designed for fault and residual current monitoring in earthed power supply systems (TN 

and TT systems) where an alarm is to be activated in the event of a fault, but disconnection 

must be prevented. In addition, the device can be used to monitor single conductors, 

such as PE conductors, N-PE connections and PE-PAS connections.

The prewarning stage (50…100 % of the set response value IΔn2) allow to distinguish between

 prewarning and alarm. Since the values are measured with measuring current transformers,

 the device is nearly independent of the load current and the nominal voltage of 

the system.

• Residual current monitoring in earthed 2, 3 or 4-conductor systems

• Current monitoring of, in the normal case, de-energised single conductors 

• Socket-outlet circuits for devices which are operated unattended for a long time and 

which may not fail

• Alarm systems, safety devices

• Air conditioning systems, EDP systems

• Cooling equipment with valuable frozen goods

• Canteen kitchens

• Monitoring of earthed power supplies for stray currents

• Impact on N conductors

• Trace heating systems

Once the supply voltage Us has been applied, the start-up delay “t” starts. Measured values 

exceeded during this time do not influence the switching state of the alarm relays.

Residual current monitoring takes place via an external measuring current transformer. 

The actual measured value is indicated on the LCD. In this way any changes, for example 

when circuits are connected to the system, can be recognised easily. 

If the measured value exceeds one or both response values, the response delays ton1/2 

begin. Once “ton1/2” have elapsed, the selected alarm relays switch). If the release value is 

not reached before the response delay “ton” has elapsed, the alarm LEDs “AL1/AL2” do 

not light up and the alarm relays do not switch. The set release time “toff” begins when 

the measured value again falls below the release value (response value minus hysteresis) 

after the switching of the alarm relays. When “toff” has elapsed, the alarm relays switch 

back to their initial position. If the fault memory is enabled, the alarm relays remain in the 

alarm state until the reset button is pressed or until the supply voltage is interrupted. The 

device function can be tested using the test button. Parameters are assigned to the device 

via the LCD and the control buttons on the front panel; this function can be password-protected.

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