Bender RCMA420-D-2 AC/DC Residual Current Monitor, 10-500 mA

A residual current monitor that also sees DC fault currents

The Bender RCMA420-D-2 is an AC/DC-sensitive residual current monitor (type B per IEC 62020 and IEC 60755) for earthed TN and TT systems where DC and AC fault currents can occur. The datasheet names loads with six-pulse rectifiers or one-way rectifiers with smoothing, such as converters, battery chargers and construction-site equipment with frequency-controlled drives. Residual current is measured through an external CTUB101-CTBC measuring current transformer, so the device is nearly independent of the nominal voltage and load current of the monitored system. Two separately adjustable response ranges distinguish a prewarning (50 to 100 % of the alarm value) from the main alarm.

The RCMA420-D-2 is the 70 to 300 V supply version; the article number is B94043002 for screw terminals and B74043002 for push-wire terminals. The -1 version takes 9.6 to 94 V DC or 16 to 72 V AC. The measuring current transformer is not included.

Technical specification

Choosing the measuring current transformer

The transformer decides the cable size that can pass through. Bender lists CTUB101-CTBC20 (20 mm diameter, B78120010), CTBC35 (35 mm, B78120012) and CTBC60 (60 mm, B78120014) and the P versions (B78120020, B78120022, B78120024). Pre-made connection cables CTX-100 (1 m, B98110080), CTX-250 (2.5 m), CTX-500 (5 m) and CTX-1000 (10 m) join transformer and monitor. The monitoring of the transformer connection switches the alarm relays without delay if a lead is broken, and the alarm LEDs flash with error code E.01. A second cascaded transformer is not monitored.

Installation notes

• Pass all live conductors, including N, through the same transformer window; do not pass PE.
• Keep the transformer cable short and away from power cables to avoid pick-up.
• Set IDn2 according to the protection concept; the default of 30 mA is a factory setting, not a recommendation for every plant.
• Fault memory is on by default; reset with the R button or by interrupting the supply.
• UL applications require 60/70 C copper conductors.

Where it is used

Residual current monitors give early warning in TN and TT systems feeding converters and chargers, such as UPS rooms, EV charging and variable-speed pumping stations. A monitor only alarms; the shut-down decision is left to the plant. See the relays category for other Bender devices.

Selection and installation notes

Insulation and residual current monitoring devices are selected from the system type (IT, TN or TT), the system voltage, the leakage capacitance and the alarm levels needed. Connect the device to the system and to earth as the manual shows, set the response values from the system design, check the coupling or measuring current transformer and its wiring, and test the alarm and relay outputs after commissioning. Do not do an insulation test of the plant with the monitor connected unless the manual allows it.

Information needed for a quotation

Send the full model code, the quantity, the delivery location in Oman or the GCC, the intended use and any accessories needed, so that the complete package can be quoted together.

Documents and supply information

The manufacturer data sheet is attached to this page and should be read together with the project specification and the site risk assessment before a purchase is confirmed. Ratings, standards and dimensions are quoted as printed on that sheet. Lead time, stock position and certificates available with the shipment are confirmed in the quotation, and we supply to Oman and the wider GCC region for industrial, utility and building services projects.

Related Bender products: Bender RCMS460-D-2 12-Channel Residual Current Monitor, Bender isoUG425-D4-4 Earth Fault Monitor for 12-120 V DC, Bender NGRM700 Neutral Grounding Resistor Monitor, Bender EDS440-L-4 ISOSCAN Insulation Fault Locator, Bender MK2430-11 COMTRAXX Remote Alarm Indicator with 12 Inputs and Bender VMD460-NA-D-2 Network and System Protection Relay.