IEC 61557-11:2020

IEC 61557-11 ®
Edition 2.0 2020-06
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Electrical safety in low voltage distribution systems up to 1 000 V AC
and 1 500 V DC – Equipment for testing, measuring or monitoring of protective
measures –
Part 11: Effectiveness of residual current monitors (RCM) type A and type B in
TT, TN and IT systems
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IEC 61557-11 ®
Edition 2.0 2020-06
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Electrical safety in low voltage distribution systems up to 1 000 V AC

and 1 500 V DC – Equipment for testing, measuring or monitoring of protective

measures –
Part 11: Effectiveness of residual current monitors (RCM) type A and type B in

TT, TN and IT systems
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 17.220.20; 29.080.01; 29.240.01 ISBN 978-2-8322-8578-7

– 2 – IEC 61557-11:2020 RLV © IEC 2020
CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 6
4 Requirements . 8
4.1 General . 8
4.2 Functions . 8
4.2.1 Operating test . 8
4.2.2 Non-operating test . 10
4.2.3 Test of actuating time . 10
4.3 Prevention of danger by fault voltages exceeding 50 V a.c. or 120 V d.c. in
the monitored system during measurement Fault voltages exceeding U . 11
L
4.4 Prevention of danger caused by overvoltages when the system is connected
Overvoltage . 11
Electromagnetic compatibility (EMC) .
5 Marking and operating instructions . 11
5.1 Markings . 11
5.2 Operating instructions . 12
5.2.1 General . 12
5.2.2 Information . 12
5.2.3 Warnings . 12
6 Tests . 12
6.1 General . 12
6.2 Operating uncertainty . 13
6.3 Test of protection against high fault voltages . 14
6.4 Test of overvoltage . 14
Annex A (informative) Differences between RCMs and RCDs .
Annex B (informative) Safety aspects, test methods and applications .
Bibliography . 23

Figure 1 – Maximum steepness of stepwise rising smooth direct test current (I ) .
T
Figure 2 – Maximum increase of linearly increasing smooth direct test current (I ) .
T
Figure 1 – Maximum step size of increasing smooth direct test current (I ) . 9
T
Figure 2 – Maximum gradient of linearly increasing smooth direct test current (I ) . 9
T
Figure 3 – Example for linearly increasing smooth direct test current (I ): I = 30 mA . 10
T ∆n
Figure A.1 – Typical installation with a combination of RCDs and RCMs .

Table 1 – Calculation of operating uncertainty . 14
Table A.1 – Normative reference and definition of function of RCM and RCD .
Table A.2 – Requirements for testing RCMs according to product standard
IEC 62020:1998 .
Table A.3 – Main technical differences between RCMs and RCDs .

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRICAL SAFETY IN LOW VOLTAGE DISTRIBUTION
SYSTEMS UP TO 1 000 V AC AND 1 500 V DC –
EQUIPMENT FOR TESTING, MEASURING OR
MONITORING OF PROTECTIVE MEASURES –

Part 11: Effectiveness of residual current
monitors (RCM) type A and type B in TT, TN and IT systems

FOREWORD
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This redline version of the official IEC Standard allows the user to identify the changes
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been made. Additions are in green text, deletions are in strikethrough red text.

– 4 – IEC 61557-11:2020 RLV © IEC 2020
International Standard IEC 61557-11 has been prepared by IEC technical committee 85:
Measuring equipment for electrical and electromagnetic quantities.
This second edition cancels and replaces the first edition published in 2009. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) document title modified to include all types of RCM;
b) terms aligned with IEC 60050;
c) addition of requirements for testing new types of RCM;
d) moving of requirements for RCM Type B from former Annex A to main body text;
e) alignment of the structure with that of the whole IEC 61557 series.
The text of this International Standard is based on the following documents:
FDIS Report on voting
85/720/FDIS 85/722/RVD
Full information on the voting for the approval of this International Standard can be found in the
report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
This International Standard is to be used in conjunction with IEC 61557-1:2019.
A list of all parts in the IEC 61557 series, published under the general title Electrical safety in
low voltage distribution systems up to 1 000 V AC and 1 500 V DC – Equipment for testing,
measuring or monitoring of protective measures, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this document using a colour printer.

ELECTRICAL SAFETY IN LOW VOLTAGE DISTRIBUTION
SYSTEMS UP TO 1 000 V AC AND 1 500 V DC –
EQUIPMENT FOR TESTING, MEASURING OR
MONITORING OF PROTECTIVE MEASURES –

Part 11: Effectiveness of residual current
monitors (RCM) type A and type B in TT, TN and IT systems

1 Scope
This part of IEC 61557 specifies the requirements for test equipment applied to the testing of
the effectiveness of residual current monitors (RCMs) of type A and type B, that are already
installed in distribution systems.
This test equipment can be used in any kind of network, such as a TN, TT or IT system. The
test equipment may can also be used for testing directionally discriminating residual current
monitors (RCM) in IT systems.
It is not the purpose of this document to verify the residual current monitors (RCM) according
to their product standards.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC/TR 60755:2008, General requirements for residual current operated protective devices
IEC 61010-1:20012010, Safety requirements for electrical equipment for measurement, control,
and laboratory use – Part 1: General requirements
IEC 61326-2-2, Electrical equipment for measurement, control and laboratory use – EMC
requirements – Part 2-2: Particular requirements – Test configurations, operational conditions
and performance criteria for portable test, measuring and monitoring equipment used in low-
voltage distribution systems
IEC 61557-1:2019, Electrical safety in low voltage distribution systems up to 1 000 V AC and
1 500 V DC – Equipment for testing, measuring or monitoring of protective measures – Part 1:
General requirements
IEC 61557-6, Electrical safety in low voltage distribution systems up to 1 000 V AC and
1 500 V DC – Equipment for testing, measuring or monitoring of protective measures – Part 6:
Effectiveness of residual current devices (RCD) in TT, TN and IT systems
IEC 62020:1998, Electrical accessories – Residual current monitors for household and similar
uses (RCMs)
– 6 – IEC 61557-11:2020 RLV © IEC 2020
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 61557-1, IEC 61557-
6, and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
earth fault current
I
e
current flowing to earth due to an insulation fault
[SOURCE: IEC 62020, definition 3.1.1 IEC 60050-442:1998, 442-01-23]
3.2
test current
I
T
test current superimposed by the test equipment for testing the effectiveness of the RCM
3.3
residual current
I
∆
vector sum of the instantaneous values of the current flowing in the main circuit of the RCM
(expressed as r.m.s. value)
[IEC 62020, definition 3.2.3]
RMS value of the vector sum of the currents flowing through the main circuit of the residual
current device due to an insulation fault
[SOURCE: IEC 60050-442:2019, 442-05-19, modified – The wording "instantaneous values"
has been deleted from the definition and "due to an insulation fault" has been added.]
3.4
rated residual operating current
I
∆n
value of residual current assigned by the manufacturer which causes the RCM to operate under
specified conditions
[IEC 62020, definitions 3.2.4 and 3.4.1 combined]
value of residual operating current assigned to the RCM by the manufacturer at which the RCM
operates under specified conditions
3.5
residual operating current
I
∆o
value of residual current which causes the residual current monitoring device to operate under
specified conditions
[IEC 62020, definition 3.2.4]
[SOURCE: IEC 60050-442:2019, 442-05-20, modified: "residual current device" has been
replaced with "residual current monitoring device" and symbol "I " has been replaced with
∆n
"I ".]
∆o
3.6
residual non-operating current
I
∆no
value of residual current at and below which the RCM does not operate under specified
conditions
[IEC 62020, definition 3.2.5]
[SOURCE: IEC 60050-442:2019, 442-05-21, modified – "residual current device" has been
replaced with "RCM" and the symbol has been omitted.]
3.7
actuating time
t
a
time taken for an RCM to change from the non-alarm state to the alarm state in response to the
sudden appearance of a residual current which exceeds the preset level
[SOURCE: IEC 62020, definition 3.3.12 IEC 62020-1:2020, 3.1.6, modified – The symbol has
been added.]
3.8
residual current monitor
RCM
device or association of devices which monitors the residual current in an electrical installation,
and which activates an alarm when the residual current exceeds the operating value of the
device
[SOURCE: IEC 62020, definition 3.3.1 IEC 62020-1:2020, 3.1.1]
3.9
RCM Type A
type of RCM for which monitoring is ensured for residual sinusoidal alternating currents and
residual pulsating direct currents, whether suddenly applied or slowly rising
[SOURCE: IEC 62020, definition 3.3.8 IEC 62020-1:2020, 5.2.6.2, modified – The words
"initiating an alarm" have been replaced with "monitoring".]
3.10
RCM Type B
type of RCM for which monitoring is ensured for residual sinusoidal alternating currents, with
residual pulsating direct currents and smooth residual direct currents independent of polarity,
whether suddenly applied or slowly rising
Note 1 to entry: RCM Type B are described in IEC 62020-1:2020, 5.2.6.4.
[IEC/TR 60755, definition 5.2.9.3, modified]
3.11
directionally discriminating RCM
type of RCM having the ability to discriminate between supply side and load side residual
currents of the monitored lines, as declared by the manufacturer
Note 1 to entry: Directionally discriminating RCM are described in IEC 62020-1.

– 8 – IEC 61557-11:2020 RLV © IEC 2020
[SOURCE: IEC 62020-1:2020, 3.1.10]
4 Requirements
4.1 General
The following requirements as well as those given in IEC 61557-1 shall apply.
In addition to the requirements of IEC 61557-1:2019, Clause 4, the requirements of Clause 4 of
this document shall apply.
4.2 Functions
4.2.1 Operating test
The testing equipment shall be capable of verifying that the residual operating current of an
RCM Type A tested with an AC test current is less than or equal to the value of the rated residual
operating current.
Testing of an RCM Type A shall be conducted with a calibrated AC current suddenly applied at
a zero crossing.
The tests shall be carried out with a sinusoidal, or mains-derived quasi-sinusoidal, test current.
If the test equipment is capable of producing half-wave test currents, testing of an RCM Type A
may be carried out alternatively with half-wave test currents and/or AC current with
superimposed ±6 mA DC according to IEC 62020.
In the case of pulsed DC current, the test equipment shall be capable of testing in both
polarities.
When testing an RCM Type B with a DC test current, it shall be verified that the residual
operating current is less than or equal to 2 times the value of the rated residual operating
current.
Testing of an RCM Type B shall be conducted separately with a suddenly applied, calibrated
AC current and a continuously rising linearly increasing smooth direct current.
The steepness slope of the continuous rate of rising linear increase shall not be greater than
2 times I / 5 s.
∆n
If the continuous rate of rising the slope of the linear increase is simulated by a stepwise or
linearly increasing test current; the increase shall not be greater than 2 times I / 30 (see
∆n
Figure 1 to Figure 3).
In both cases, the starting current shall be less than 0,2 times I .
∆n
The operating uncertainty of the increasing test current I shall not exceed ±10 % of the rated
T
residual operating current I .
∆n
The operating uncertainty of the calibrated test current I shall not exceed 0 % to +10 % of the
T
rated residual operating current I .
∆n
The test period shall be adapted to the set actuating time of the RCM and it shall be possible
to extend the test period up to 10 s.

Figure 1 – Maximum step size of increasing smooth direct test current (I )
T
Figure 2 – Maximum gradient of linearly increasing smooth direct test current (I )
T
– 10 – IEC 61557-11:2020 RLV © IEC 2020

Figure 3 – Example for linearly increasing smooth direct test current (I ): I = 30 mA
T ∆n
Key (for Figure 1 to Figure 3)
t time
I rated residual operating current
∆n
I smooth direct test current
T
∆I slope of the linear increasing test current or steps of stepwise rising test current
T
∆t time for one step for linearly increasing test current or time for steepness of continuous rising test current
A slow continuous or stepwise increase of the DC test current is required to prevent the AC
sensitive part of the RCM Type B from operating during the DC test.
Example for ∆I = 2 mA: ≥ 167 ms
T
Example for ∆I = 0,5 mA: ≥ 42 ms
T
NOTE 1 Existing leakage currents downstream can influence the verification.
NOTE 2 The actual rise time depends on the system capacitance and the resistive load of the test equipment.
NOTE 3 Smooth DC test current refers to direct current with AC ripple up to 10 % (peak to peak).
4.2.2 Non-operating test
When a test at 50 % or less of the rated residual operating current is used to test the reliability
of the RCM is included, the minimum test period shall be 10 s. The alarm shall not be activated.
When a non-operating test at 50 % or less of the rated residual operating current is included,
the operating uncertainty of the calibrated test current shall not exceed 0 % to −10 % of the
specified non-operating test current.
NOTE Existing leakage currents downstream can influence the verification.
4.2.3 Test of actuating time
If the set actuating time of the RCM is being tested with the test equipment, the setting of the
test period on the test device shall have a resolution of minimum 0,5 s ranging up to 10 s. The
setting uncertainty shall not exceed 0 % to −10 % of the set value. The test shall solely be
performed with calibrated AC test current.

Other methods for the acquisition of the actuating time via optical recognition or interfacing are
permissible.
NOTE The general function of RCMs is not to disconnect the power supply when a residual current above the value
of the rated residual operating current occurs. The RCM indicates the increase of the residual current above the
residual operating current with a signalling device, for example a lamp, buzzer, contact relay or interface-signal.
Thus, the response time may can only be tested via the visual or additional electrical detection of this signal.
According to IEC 62020-1, the response actuating time of the RCM may only amount to a
maximum of 10 s. The response time shall be specified by the manufacturer or shall be
adjustable on the device.
If the RCM is being used for the purpose of disconnection, the tests covered by IEC 61557-6
shall apply.
4.3 Prevention of danger by fault voltages exceeding 50 V a.c. or 120 V d.c. in the
monitored system during measurement Fault voltages exceeding U
L
Prevention of danger due to fault voltages exceeding U within the system under test shall be
L
ensured during the use of the test equipment. This can be achieved as follows:
– automatic disconnection in accordance with IEC 61010-1:20012010, Figure 1, if the residual
voltage is above 50 V AC or 120 V DC;
– application of test current I , gradually or permanently adjustable, where the test starts with
T
2010,
a maximum current of 3,5 mA AC or 15 mA DC in accordance with IEC 61010-1:2001
6.3.2 b), including parallel test circuits, is permitted. The possibility to change the test
current I without generating a dangerous residual fault voltage shall be clearly identifiable,
T
for instance on a voltmeter;
– in special locations, the touch voltage limit is 25 V AC or 60 V DC;
– the operating uncertainty for the detection of the fault voltage shall not exceed 0 % to −20 %
of the limit.
4.4 Prevention of danger caused by overvoltages when the system is connected
Overvoltage
If the system is connected to 120 % of the nominal voltage of the system for which the test
equipment is designed, neither the operator shall be harmed, nor the device be damaged.
Protective devices shall not be activated. If the device is intended to be used in IT systems, the
nominal voltage of the test equipment is the phase to phase line-to-line voltage.
If the test equipment is accidentally connected to 173 % of the nominal voltage in TN or TT
systems for which the test equipment is designed for the duration of 1 min, neither the operator
shall be harmed, nor the device be damaged. In this case, protective devices may be activated.
4.7 Electromagnetic compatibility (EMC)
The electromagnetic compatibility shall be in accordance with IEC 61326-2-2.
5 Marking and operating instructions
5.1 Markings
In addition to the marking in accordance with IEC 61557-1 the requirements of IEC 61557-
1:2019, 5.1, the following information shall be provided on the measuring equipment.
Rated residual operating current or rated residual operating currents of the RCM for which the
test equipment has been designed for an actuating time of 10 s.

– 12 – IEC 61557-11:2020 RLV © IEC 2020
NOTE Other rated residual operating currents for lower a shorter duration of the actuating times may can be marked
in addition.
The maximum voltage to earth and the rated measuring category shall be marked.
5.2 Operating instructions
5.2.1 General
The operating instructions shall state the following in addition to the statements given in
IEC 61557-1.
In addition to the requirements of IEC 61557-1:2019, 5.3, the operating instructions shall
include the information and warnings set out in 5.2.2 and 5.2.3.
5.2.2 Information
a) Information about special test configurations to avoid unintended tripping of residual current
devices (RCD) (see Annex B);
b) information to avoid unintended influences on the operation of the system;
c) information for recalibration cycles and safety tests of the test equipment after repair and
instructions for periodical tests.
5.2.3 Warnings
a) If the detecting circuit for the fault voltage has no probe and if a possible voltage between
the protective conductor and earth influences the measurements, a warning shall be
included.
b) Where the detecting circuit for the fault voltage uses the N-conductor as a probe, a warning
shall be given to test the connection between the neutral point of the distribution system
and earth before the test is started; a possible voltage between the N-conductor and earth
may influence the measurements.
c) A warning that leakage currents in the circuit following the RCM may influence
measurements and test results.
d) The earth electrode resistance of a detecting circuit for the fault voltage with a probe shall
not exceed the value stated by the manufacturer.
e) A warning that the potential fields of other earthed installations may influence the
determination of the fault voltage.
f) A warning that for special locations the touch voltage is limited to 25 V AC or 60 V DC.
6 Tests
6.1 General
The following tests in addition to those required according to IEC 61557-1 shall be executed.
In addition to IEC 61557-1:2019, Clause 6, the following tests shall be performed.
Tests shall be carried out with rated residual operating currents, in addition to the values of the
non-operating test currents I , if applicable.
T
The test circuit shall be adapted to test the function of the fault voltage detection circuit at the
limits of the fault voltage for which the equipment is designed and in addition at the appropriate
R = R for each range.
A Amax
The test circuit shall be adapted to each test method employed. The manufacturer's instructions
shall be heeded observed.
NOTE
U
L
RI=
Amax Δo
I
Δn
U
L
R =
Amax
I
T
where
U is the conventional touch voltage limit;
L
I is the test current superimposed by the test circuit;
T
R is the total earthing resistance (R = R );
A A Amax
I is the rated residual operating current;
∆n
I is the residual operating current.
∆o
6.2 Operating uncertainty
The operating uncertainty applies in accordance with the test conditions specified in
IEC 61557-1:2019 and, in addition, the following requirements apply:
– the protective conductor is free of extraneous voltage,
– the system voltage remains constant during tests,
– the circuit behind the RCM is free of leakage currents,
– sinusoidal half-wave or full-wave current with rated frequency, respectively smooth direct
current (see 4.1),
– the voltage on the protective conductor relative to earth or N shall be less than 1 Vrms;
– the system voltage remains stable within ±1 V during the measurement;
– the circuit following the residual current protective device carries a negligible leakage
current;
– sinusoidal half-wave current with rated frequency, or sinusoidal full-wave current with rated
frequency, or smooth direct current (see 4.2);
– the AC test current I shall be switched on at a zero crossing;
T
– the test period shall be 10 s for the maximum test current for which the test equipment is
designed;
– the time limit may be omitted when testing with current greater than 500 mA;
– the resistance of the probes is within the limits stated by the manufacturer.
The operating uncertainty shall be determined in accordance with Table 1. In this process, the
intrinsic uncertainty shall be determined under the following reference conditions:
– nominal voltage of the rated range of the device,
– nominal frequency of the rated range of the device,
– reference temperature 23 °C ± 2 °C,
– reference position in accordance with the manufacturer's instructions,
– protective conductor free from extraneous voltages,
– 100 Ω resistance of the auxiliary earth electrode in a TT system.
The operating uncertainty thus evaluated shall not exceed the limits specified in 4.1 to 4.2.
a) Compliance with the permissible operating uncertainty when detecting the fault voltage
shall be tested for measurements with and without a probe.

– 14 – IEC 61557-11:2020 RLV © IEC 2020
b) Compliance with the requirements in accordance with 4.5 shall be tested (routine test).
c) The overload protection in accordance with 4.6 shall be tested (type test).
d) Compliance with the tests in this clause shall be recorded.
Table 1 – Calculation of operating uncertainty
Intrinsic uncertainty or Reference conditions or Designatio Requirements or test in Type of
influence quantity specified operating range n code accordance with the test
relevant parts of
IEC 61557
Intrinsic uncertainty Reference conditions A IEC 61557-11:2020, 6.2 R
Position Reference position ±90° E IEC 61557-1:2019, 4.2 R
Supply voltage At the limits stated by the E IEC 61557-1:2019, 4.2, R
manufacturer 4.3
Temperature 0 °C and 35 °C E IEC 61557-1:2019, 4.2 T
Resistance of the probes Within the limits stated by E IEC 61557-11:2020, 4.4 T
the manufacturer
System voltage 85 % to 110 % of the nominal E IEC 61557-11:2020, 4.4, T
voltage 4.5
Operating uncertainty IEC 61557-11:2020, 4.1 R
BA=±+ E
∑ i
i
6.2
A = intrinsic uncertainty
E E = variations
n
i
B
R = routine test B % =±× 100 %

F
T = type test
F = fiducial value
6.3 Test of protection against high fault voltages
Compliance with the permissible operating uncertainty when detecting the fault voltage shall be
tested for measurements with and without a probe (routine test).
Compliance with 4.3 shall be tested in all ranges.
6.4 Test of overvoltage
The permissible overvoltage in accordance with the requirements of 4.4 shall be tested (type
test).
I
T
∆I
T
∆t
t
IEC  2359/08
∆I ≤  2 I / 30      ∆I / ∆t ≤ 2 I / 5 s
T ∆N T  ∆N
Key (for Figures 1 to 3)
t time
I rated residual operating current
∆N
I smooth direct test current
T
∆I steepness of continuous rising test current or steps of stepwise rising test current
T
∆t  time for one step for stepwise rising test current or time for steepness of continuous rising test current
Figure 1 – Maximum steepness of stepwise rising smooth direct test current (I )
T
I
T
∆I
T
∆t
t
IEC  2360/08
∆I / ∆t ≤ 2 I / 5 s
T  ∆N
Figure 2 – Maximum increase of linearly increasing smooth direct test current (I )
T
– 16 – IEC 61557-11:2020 RLV © IEC 2020

I
T
∆I
T
∆t
t
IEC  2361/08
∆I ≤  2 × 30 mA / 30 ≤ 2 mA
T
Example for ∆I  = 2 mA: ∆t ≥ (2 mA × 5 s) / (2 × 30 mA) ≥ 167 ms
T
Example for ∆I = 0,5 mA:   ∆t ≥ (0,5 mA × 5 s) / (2 × 30 mA) ≥ 42 ms

T
NOTE 1 Existing leakage currents downstream may influence the verification.
NOTE 2 The actual rise time depends on the system capacitance and the resistive load of the test equipment.
NOTE 3 Smooth d.c. test current refers to direct current with a.c. ripple up to 10 % (peak to peak).
NOTE 4 A slow continuous or stepwise increase of the d.c. test current is required to prevent the a.c. sensitive part
of the RCM type B from operating during the d.c. test.
Figure 3 – Example for linearly increasing smooth direct test current (I ): I = 30 mA
T ∆N
Annex A
(informative)
Differences between RCMs and RCDs

A.1 Scope
This Annex A gives guidelines for specifying the differences between residual current monitors
(RCMs) and residual current protective devices (RCDs). The understanding is important in the
design of test equipment and for testing RCMs in electrical installations.
A.2 Reference documents and definition of function
Table A.1 shows the differences by definition according to the respective product standard.
Table A.1 – Normative reference and definition of function of RCM and RCD
Product Standard Definition of function
RCM IEC 62020:1998, 3.3.1 A residual current monitor (RCM) is a device or an association of
devices which monitors the residual current in an electrical installation,
and which activates an alarm when the residual current exceeds the
operating value of the device
RCD IEC/TR 60755:2008, 3.3.1 A residual current device (RCD) is a mechanical switching
device or association of devices designed to make, carry and
break currents under normal service conditions and to cause the
opening of the contacts when the residual current attains a
given value under specified conditions

IEC 62020 is the only product standard for RCMs. RCMs covered by this standard are not
intended to be used as protective devices, but may be used in conjunction with protective
devices (see IEC 60364-4-41).
IEC/TR 60755 is the basic product standard for RCDs. Variations of RCDs are covered by other
product standards, for example IEC 61008-1 and IEC 60947-2.
If RCMs are used together with switching devices and this combination fulfils the respective
RCD standards, for example IEC 60947-2 for MRCDs, this combination has to be tested in the
installation with equipment covered by IEC 61557-6.
A.3 Requirements from product standards for testing RCMs
Table A.2 shows the requirements from the product standard IEC 62020:1998 which should
apply when testing RCMs in installations.

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Table A.2 – Requirements for testing RCMs according
to product standard IEC 62020:1998
Requirement Explanation Consequence for testing
Type of RCM Type A (type a.c. is not allowed) Test with the applicable waveforms
Type B existing, but is not covered by IEC 62020
Rated residual Values to be defined by the manufacturer Test with the values defined by the
operating current manufacturer and appropriate
Preferred values are : 0,006 A, 0,01 A, 0,03 A,
device settings for adjustable
0,1 A, 0,3 A, 0,5 A
devices should be considered
Values can be fixed or adjustable
The operating tolerances of the
RCM (residual operating and non-
operating current) are equal to that
of RCDs
Actuating time For RCMs only a maximum actuating time is Defined or adjusted actuating times
defined: 10 s should be considered
The actuation time can be fixed or adjustable

Preferred values of RCMs type A: 50 Hz and/or 60 Hz – RCDs type A: preferred value is
rated frequency manufacturer can define other values, but 50 Hz
frequency response is not defined in the product
RCDs type B: frequency response is
standard
limited to 1 000 Hz
RCMs type B: see RCDs type B
Indication of the fault RCMs should be provided with means for Different to RCDs, tripping of the
condition indicating the fault condition RCM can not be recognized due to
switching off of the monitored
RCMs may be fitted with a resetting function to
voltage
manually reset the RCM to the non-alarm state
after removal of the fault. RCMs not fitted with Recognition of tripping can only be
resetting function should reset automatically performed by monitoring or
after removal of the fault controlling the respective alarm
function:
Where an audible alarm is provided in addition,
the audible alarm should reset automatically Examples of alarm functions:
after removal of the fault
– visual indicator (required)
– audible alarm (optional)
– alarm contact (optional)
– alarm via digital interface
(optional)
Disconnection of an If the RCM is equipped with an external residual Disconnection is normally checked
external CT current transformer (CT), the RCM should give a during the operating test of the RCM
warning, if the CT is disconnected

A.4 Main technical differences between RCMs and RCDs
Table A.3 shows the main technical differences between RCMs and RCDs.

Table A.3 – Main technical differences between RCMs and RCDs
Function RCM RCD
Operation / Tripping (actuating) Operation is indicated on the RCM Tripping is primarily indicated by
by a visual signal on the front of the switching off the voltage
device. Additional signals for
Tripping can be recognized on any
indicating operation may be :
outlet or part of the installation
– audible alarm, where the test is performed
– alarm contacts,
– digital interface.
Operation can not be recognized on
an outlet, where the test is
performed and which is located
outside the area where the alarm on
the RCM itself can be recognized
Actuating time Actuating time can be anywhere The maximum actuating time of
between 0 s and 10 s RCDs is defined in the respective
RCD standards
The set or fixed actuating time
should be respected Actuating time has to follow the time
characteristics of the RCD
Actuating time for RCMs relate to 1
standards for 1 time I ,
∆N
× I only
∆N
2 times I , 5 times I
∆N ∆N
Operating / Tripping values Operating values can be fixed or Tripping values are fixed or
adjustable. Adjustment can be in adjustable in steps. The set values
steps or steplessly by switches, are indicated on the front of the
potentiometers or by menu settings device
via displays
The set operating values are visible
on the front of the RCM
Supply voltage dependency RCMs are voltage dependent RCDs type A may be voltage-
devices dependent or voltage-independant.
Standards for voltage-dependent
RCDs are under consideration
RCDs type B are generally voltage
dependant
Indication of the value of the Some RCMs are equipped with RCDs generally have no such
measured residual current functions for the indication of the indication
residual current
Multi-channel devices RCMs can be multi-channel devices. Generally RCDs are single channel
In this case several residual current devices
sensors (CTs) are connected to one
device. Setting operating values and
signalling alarms are performed on
this device
A.5 Special considerations for testing RCMs in the installation
The following points should be considered when testing already installed RCMs:
– operation of the RCM should be recognized by watching the alarm indicator on the front of
the RCM or on a remote indication device;
– the settings of the test equipment should allow stepwise or continuous increase of the test
current;
– for testing the operating value the time for each step or gradual increase of the test current
should respect the setting of the actuating time on the RCM ( 0…10 s).
If other fault-indication is provided, for example audible or remote indications via alarm contact
or digital interface, these indications should be tested as well.
Figure A.1 shows a typical installation where RCMs are installed in addition to RCDs.

– 20 – IEC 61557-11:2020 RLV © IEC 2020

RCM type B
RCM type A
RCD
RCD
Type A
Type B
MDP
M
VFD
Multichannel
RCM type A
RCD RCD RCD RCD
Type A Type A Type A
Type A
SDP
Socket outlets
IEC  2362/08
Key
MDP main distribution panel
S
...