benderAC/DC sensitive residual current monitor RCMA475LY

Residual current monitor

RCMA475LY

AC/DC sensitive residual current monitor

for TN and TT systems (AC, DC, pulsating DC currents)

Product description

The AC/DC sensitive residual current monitor RCMA475LY is designed for monitoring 

earthed power supply systems (TN and TT systems) where DC fault currents or residual 

currents continuously greater than zero may occur. These are in particular loads containing 

six-pulse rectifiers or one way rectifiers with smoothing, such as converters, battery chargers, 

construction site equipment with frequency-controlled drives. 

The prewarning stage (50 % of the set response value IΔn1) 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.

Application

• AC/DC sensitive residual current monitoring in earthed two, three or four conductor 

systems (TN and TT systems)

• AC/DC sensitive current monitoring of single conductors de-energised under normal 

conditions (e.g. N and PE conductors)

• Variable-speed drives

• Uninterruptible power supply systems (UPS)

Function

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

When the current respectively the residual current exceeds the set response value, the alarm 

LED lights and the associated alarm relay switches when the set response delay has elapsed.

The alarm messages are stored. The fault memory can be reset by pressing the reset button. 

The device function can be tested using the test button. 

The currently measured value in per cent related to the set response value is indicated on 

the LED bar graph indicator. 

Device features

• Internal measuring current transformer 

ø 18 mm

• Two response values

alarm IΔn1: 30…500 mA (0…700 Hz)

prewarning IΔn2: 50 %/100 % of IΔn1

• Response delay, adjustable 0…10 s 

(prewarning 0/1 s) 

• Two separate alarm relays with one 

changeover contact each

• N/O or N/C operation, selectable 

• Fault memory 

• Combined test/reset button

• Connection external test and reset button

• LED bar graph indicator IΔn 0…100 % 

• Connection external measuring instrument 

IΔn 0…100 % 

• Sealable transparent cover

• External supply voltage

• Type B acc. to IEC/TR 60755

1 - Supply voltage US, see ordering information 

(6 A fuse recommended)

2 - External measuring instrument

3 - External test and reset button "T/R"

4 - Alarm relay (Alarm):

switches when the fault current exceeds the response value of IΔn1.

5 - Alarm relay (prewarning):

switches when the fault current exceeds 50 % or 100 % of IΔn1.

6 - Internal measuring current transformer

Do not route the PE conductor through the measuring current 

transformer!

.

1 - Combined test/reset button "TEST/RESET"; short-time pressing (< 1 s) = RESET, long-time pressing (> 2 s) = TEST.

2 - Power On LED "ON": lights when the device is in operation 

and flashes when the measuring range is exceeded.

3 - Alarm LED "ALARM": lights when the fault current exceeds 

the set response value and flashes when 50 % of the set response value are reached.

4 - LED bar graph indicator, shows the measuring value in per 

cent related to the preset response value.

5 - Potentiometer for setting the response delay (0…1 s).

6 - Potentiometer for setting the response value (x 1…10 mA).

Setting of the DIP switches (white = switch position)

7 - Contact 21-22-24 (prewarning)

A - at 50 % of IΔn1

B - at 100 % of IΔn1

8 - Response delay prewarning

A - Delay 1 s

B - Delay 0 s

9 - Alarm relay

A - N/O operation

B - N/C operation

10 - Response range

A - 30 mA x 1…10

B - 50 mA

11 - Response delay

A - Setting value t/s x 10

B - Setting value t/s x 1

Technical data

Insulation coordination acc. to IEC 60664-1

Rated insulation voltage AC 250 V

Rated impulse withstand voltage/pollution degree 4 kV/3

Voltage ranges

Supply voltage US see ordering information

Operating range of US 0.85…1.1 x US

Frequency range of US DC/50…60 Hz

Eigenverbrauch ≤ 3.5 VA

Measuring circuit/response values

Internal measuring current transformer ø 18 mm

Operating characteristics acc. to IEC/TR 60755 Type B

Rated residual operating current IΔn2 (prewarning) 50 %/100 % of IΔn1

Response delay tv 0/1 s

Rated residual operating current IΔn1 (alarm) 30…500 mA

Response delay tv, adjustable 0…10 s

Rated frequency 0…700 Hz

Relative uncertainty of the response value 0…25 %

Hysteresis approx. 25% of the response value

Response time tan at IΔn1 = 1 x IΔn1/2 (tv = 0 s) ≤ 70 ms

Response time tan at IΔn1 = 5 x IΔn1/2 (tv = 0 s) ≤ 40 ms

Displays

LED bar graph indicator 0…100 %

LEDs Power On, prewarning, alarm

Inputs/outputs

Test and reset button internal/external

Cable length for external test and reset button ≤ 10 m

Current source for external measuring instrument 0…100 % DC 0…400 µA

Load ≤ 12.5 kΩ

Switching elements

Number of switching elements 2 x 1 changeover contact

Operating principle, adjustable N/C operation/N/O operation

Electrical endurance, number of cycles 12000

Rated contact voltage AC/DC 150 V