by Viv Cohen
Circuit Breaker Industries, Private Bag
2016, Isando, 1600 South Africa
This paper introduces and defines the concepts of Electromagnetic
Interference (EMI) and Electromagnetic Compatibility (EMC), together with their
relationship to Quality of Supply (QOS). Without delving into the complex detail
of requirements in individual test standards, the paper introduces the identified
low frequency and high frequency EMC phenomena that have been covered in the
new IEC 1000 series of documents, both from the points of view of emission and
immunity. The impact of these disturbances on low voltage protection equipment
such as moulded case circuit breakers and earth leakage circuit breakers in
particular are examined, but the principles are applicable to all equipment
connected to the low voltage installation. The phenomena of transient surges
and harmonics together with their effects on performance and survival of connected
equipment are given particular attention.
Over the past decade many papers have been written on the subject of EMC (Electromagnetic
Compatibility), with discussions being driven by the need to comply with the
EC Directive on EMC, which became a mandatory requirement for all goods sold
in Europe after January 1 1996. Outside Europe, few countries have such regulations
in place, so unless product is exported to Europe, there is not much incentive
to address the problems of electromagnetic emission by products or systems.
Similarly, the question of a product or system’s immunity to the effects of
disturbances on the electricity supply network only receives attention after
malfunctions have been experienced. Electromagnetic interference phenomena,
which have been associated with broadcasting and telecommunications industries
in the past, are now of increasing concern to power system engineers. In recent
times a proliferation of articles and discussions on the subject of "Quality
of Supply" have captured the interest of power system engineers, but often
without addressing the growing need for engineers outside of the electrical
utilities industry to understand even the basic concepts and need for electromagnetic
compatibility (EMC) in low voltage systems.
QUALITY OF SUPPLY
Electricity Supply Utilities are particularly conscious of the Quality of
Supply (QOS) of the
product that they deliver to their bulk consumers. In theory, regulations on
the quality of supply of electricity delivered, are applicable up to the point
of consumption of ALL consumers. However, little attention is usually given
beyond the high and medium voltage networks. It is unusual to regulate supply
quality on the low voltage system outside of the limits that are applied to
voltage and frequency deviations. By definition, QOS applies to all aspects
of EMC, with the most visible phenomena being Voltage Dips or Depressions and
Harmonics. In South Africa, quality of supply standards for application in the
Electricity Supply Industry are documented in the Rationalized User Specification
NRS 048 : 1996.
In recognition of the high incidence of lightning activity in many parts of
South Africa, there is an opinion in some quarters that at the very least, some
minimum degree of control on the amplitude of voltage surges arriving at the
low voltage point of supply is necessary. Furthermore, since solidly earthed
low voltage distribution systems are recommended in NRS 048, some mention of
earthing system requirements appears to be appropriate. The debate on these
WHAT is EMC ?
Electromagnetic Compatibility(EMC) is achieved when the operation of
equipment or products -
- Is unaffected by
the operation of other equipment.
- Results in no adverse
effects on other equipment.
Electromagnetic Interference (EMI)with the operation of products or
systems is the reason for the need for
EMC requirements are commonly divided into :
- Low frequency phenomena
- High frequency phenomena
- Electrostatic phenomena
One unfortunate consequence of modern technology is that power supply networks
and the electromagnetic spectrum are being polluted with unwanted signals ranging
from d.c. through to high frequencies approaching those of visible light.
Both low frequency and high frequency disturbances are divided into conducted
and radiated disturbances.
Electromagnetic compatibility is the discipline which attempts to overcome,
or at least minimise the effects of mismatch between equipment and the operating
environment in accordance with agreed standards and regulations.
The principal disturbances in the electromagnetic spectrum are generally classified
as follows :
Conducted low frequency
- Harmonics, Interharmonics
- Signalling Voltages
- Voltage amplitude variations
- Voltage Dips
- Voltage interruptions
- Voltage unbalance
- Power frequency variations
-Induced low freq. voltages
- d.c. in a.c. networks
Radiated low frequency field
- Magnetic fields
(continuous or transient)
- Electrical fields
Conducted high frequency
- Induced voltages or currents
- Unidirectional transients
- Oscillatory transients
Radiated high frequency
- Magnetic fields
- Electric fields
(continuous or transient)
High altitude nuclear electromagnetic pulse
The phenomena identified as having the greatest impact on the performance of
equipment connected to the low voltage system have been addressed and included
in the test requirements of the relevant product standards. There are however
some phenomena that remain under consideration whilst the importance of their
impact is being assessed. These include :
- Induced low frequency voltages
- Electric fields
- High altitude nuclear electromagnetic pulse
WHY IS THERE CONCERN ?
The use of electronically powered and controlled equipment, devices and appliances
in large industries or by individuals in residential, commercial or industrial
environments, has resulted in a dramatic increase in the generation of interference
signals that are polluting the low voltage networks. The effects of EMI are
of concern because of the consequential malfunction of key electrical and electronic
systems. Such systems could include for example, manufacturing industries, telecommunication
services and defence systems. In the extreme, public health and safety could
Outside of exporters to Europe, only limited recognition of the problems associated
with EMC exist, and little attention is given to the subject.
SPECIFICATIONS and STANDARDS
The one organisation that has been most actively involved in the development
and preparation of Standards and publications covering EMC, is the International
Electrotechnical Commission (IEC). The IEC has defined three types of Standards.
These include :
- Basic standards
- Generic standards
- Product standards
Much of the original IEC work on radiated emission has been based on publications
developed by CISPR which is the IEC’s international special committee on radio
interference. In addition, several ANSI/IEEE publications have been used as
source references in defining the wave shapes of transient surge voltage and
current. Basic EMC standards and reports are produced by IEC technical committee
TC77 and its sub-committees. The EMC test requirements contained in IEC product
standards are determined by the individual IEC product committees, sometimes
using also generic standards that cover particular product groups. Where already
existing product test requirements can be shown to cover cer
The initial serious work on EMC standards within the IEC began in the early
1980’s with the publication of two separate sets of documents, prepared by different
IEC technical committees. These included the IEC 801 series of documents prepared
by Technical committee TC 65, and the IEC 555 series of documents prepared by
technical committee TC77.
IEC 801 covered EMC for industrial process measurement
and control equipment.
IEC 555 dealt with disturbances in supply systems
caused by household appliances and similar electrical equipment.
Largely driven by more pressing demands of the EC directive on EMC, both IEC
801 and IEC 555 series of documents have been replaced by the new IEC
1000 series of documents.
For the present, IEC 1000 is divided into six separate parts, and further subdivided
into sections which are being published either as International Standards or
as Technical Reports.
- Fundamental principles
- Description of the environment
-Classification of the environment
- Compatibility levels
- Emission limits
- Immunity limits
Testing and measurement
- Measurement techniques
- Testing techniques
Installation & mitigation
- Installation guidelines
- Mitigation methods & devices
EMC Immunity Test Standards
A number of Basic Standards covering EMC Immunity requirements have been produced
by IEC TC77 and it’s sub-committees under the banner of the new IEC 1000-4 series
of documents. The following list indicates the current status of these
IEC Immunity test publications:
Subject / Test
Overview of Immunity tests
Electrostatic Discharge tests
Radiated, radio frequency, electromagnetic
Fast transient/burst immunity tests
Surge Immunity test
Immunity to conducted disturbances duced
by r.f. fields
General guide on Harmonics and
Power frequency magnetic field immunity
Pulsed magnetic field immunity
Damped oscillatory magnetic field immunity
Voltage dips, short interruptions and
Oscillatory waves immunity test
Harmonics, Inter-harmonics and
mains signalling immunity
Immunity to Conducted disturbance
Ripple on d.c. power supply
Variation of power frequency
# Still in preparation
EMC STANDARDS FOR RCD’S
The EMC requirements for RCD’s (known as ELCB’s in South Africa and GFI’s in
the USA) have been covered in the relatively new standard IEC 1543 which was
published in April 1995.
IEC 1543 is one of the betterexamples of consolidated
work on EMC within the IEC. It addresses both emission and immunity requirements
for Residual Current Devices. Whilst IEC 1543 has been
directed specifically at RCD’s for household and similar use, it’s value has
been recognised by other IEC committees and it is already being used as a reference
document for the updating of EMC requirements for similar devices covered in
IEC 947-2 - Circuit Breakers. For SAFETY products such as residual current
circuit breakers, the possible problems that could result from electromagnetic
interference are of particular concern. At best, such interference can lead
to unwanted tripping of the RCD. At worst, the RCD could malfunction in the
presence of extraneous radiated or conducted signals. Several decades of installation
and application experience with millions of RCD’s in a variety of installation
environments has assisted manufacturers of these devices in identifying most
of the application problems that can arise due to disturbances in the electrical
During the preparation phase of EMC standards for RCD’s, it was realised that
at least some of the existing performance tests that had been included in the
RCD product standards, already addressed a portion of the generalised EMC test
In general these are included in the low frequency EMC immunity requirement.
The following are deemed to be covered by existing test requirements in the
RCD product standards:
- Voltage fluctuation
- Voltage dips
- Voltage interruptions
- Voltage unbalance
- Power frequency variations
In recognition of the specific safety functions of RCD’s, and independent of
the need created by the implementation of the EC directive on EMC, IEC 1543
was produced to deal with the EMC aspects that had already been identified through
the application and operation of RCD’s. This International Standard includes
definitions, standard electromagnetic conditions, conditions of operation in
service and electromagnetic tests necessary for devices providing residual protection.
The framework of the document was based on recommendations given in the IEC
1000 series of documents. The existing performance tests that had been deemed
to cover some of the low frequency EMC immunity tests were then “plugged-in”
to the framework. The document was completed using wherever possible, the work
completed and in progress in the IEC 1000 series.
EMC Emission of RCD’s
As a general rule within the IEC, it has been determined that for equipment
not incorporating electronic circuits, electromagnetic disturbances can only
be generated by equipment during occasional switching operations. The duration
of these disturbances is of the order of milliseconds. The IEC has concluded
that the consequences of these emissions are relatively insignificant and can
be considered as part of the normal electromagnetic environment of low voltage
installations. Therefore in such cases the requirements for electromagnetic
emission are deemed to be satisfied and no verification is necessary. Emission
tests according to CISPR 14 are however required for those RCD’s that contain
continuously operating oscillators and/or microprocessors.
Performance criteria of RCD’s
The performance criteria that are used to determine the immunity of RCD’s to
the effects of electromagnetic interference are based on :
- Freedom from nuisance tripping
- Non-interference with the ability of the RCD
to perform it’s safety functions.
Surge Voltages and Surge Currents
The propagation of voltage and current surges in low voltage wiring systems
are of particular concern to consumers of electricity in considering :
- Insulation co-ordination in the fixed wiring
- Damage to fixed equipment and appliances
- Maloperation of equipment and processes
One of the most visible effects of mains borne lightning or switching surges
is the unwanted tripping of RCD’s. Voltage surges or Current surges that result
from induced voltages can cause nuisance tripping in RCD’s due to :
- Insulation sparkover in the fixed installation
- Insulation sparkover in appliances
- Voltage stress on components within the
- Spurious response of the
RCD to non-damaging current surges.
In ideal situations where overvoltage control is employed together with good
insulation co-ordination, insulation sparkover should not be a problem. This
however is not always the case, and RCD’s are required to be immune to the effects
of surge currents that do not result in any permanent damage to connected equipment.
Immunity to surge currents in RCD’s is achieved in the main through two standardised
test procedures which include :
- Current oscillatory transients
- Unidirectional surge currents
Current Oscillatory transients
RCD’s are tested using a surge current generator capable of delivering a damped
oscillatory current of 200A peak. The current wave is based on the original
voltage wave that was proposed in ANSI/IEEE C62.41-1980 (see Figure 1.)
Figure 1 - Ring Wave
- [ Image unavailable ]
Based on measurements that were conducted by several independent organisations
in both Europe and the USA, this so-called 0,5 microsecond - 100kHz “ring wave”
is now considered to be reasonably representative of surge voltages appearing
on indoor low voltage power circuits.
In the outdoor and service entry environment, as well as in locations close
to the service entrance, substantial energy or current is still available. For
these locations the long established unidirectional impulses are considered
to be more applicable than the oscillatory wave. The amplitude of the impulse
voltage for testing RCD’s according to IEC 1008 is 5kV peak common mode and
4kV peak in differential mode.
Figure 2 - Discharge current
waveform - [ Image unavailable ]
In the case of RCD’s where a higher degree of immunity to current surges is
required, a surge current having a wave shape of 8/20 microseconds as shown
in Figure 2 is used. The amplitude of the current surge is determined by the
specified surge generator impedance. Generator impedance is specified as 12
ohms for the common mode test and 2 ohms for the differential mode test.
The 8/20 microsecond Current surge is derived
from the 1,2/50 microsecond Voltage surge which
is shown in Figure 3.
Figure 3 - Open - Circuit Waveform
- [ Image unavailable ]
It has been long established that the application of unidirectional impulse
voltages of the 1,2/50 microsecond waveshape are very effective in establishing
the dielectric withstand capabilities of electrical switchgear. For certain
applications, impulse voltage testing is even replacing some power frequency
dielectric testing requirements.
It is unfortunate that in some areas, there remains confusion between EMC surge
tests and these dielectric tests which are Impulse
Voltage tests, without any need for consideration of surge currents resulting
from the voltage impulse.
Radio frequency Electromagnetic
Within the IEC 1000 series there are two separate documents that deal with
the question of Radio Frequency electromagnetic field immunity tests.
IEC 1000-4-3 covers RADIATED r.f. fields.
IEC 1000-4-6 covers CONDUCTED r.f. fields.
In both cases, the source of the disturbance is basically an electromagnetic
field, originating from intended r.f. transmitters that may act on the whole
length of cables connected to an installed equipment.
The dimensions of disturbed equipment such as RCD’s are small compared with
the wavelengths involved. The incoming and outgoing leads will therefore behave
as passive receiving antenna networks since they can be several wavelengths
long. The scope of IEC 1000-4-6 covers the frequency spectrum of 9kHz up to
80MHz. For small devices such as RCD’s, it may be possible in the future, to
test according to IEC 1000-4-6 for Conducted
radio frequency fields up to 230 MHz.
The test levels for RADIATED radio frequency electromagnetic field tests for
RCD’s are taken from IEC 1000-4-3 for the frequency spectrum 80MHz up to 1000MHz.
This radiation is often generated by such sources as small hand held radio receivers
as well as fixed and mobile radio and television transmitters.
The question of emission due to GSM digital radio telephones is still under
investigation by the relevant IEC sub committee.
Electrical fast transient bursts
In addition to the voltage and current impulse tests that are applied to RCD’s,
it has been found to be appropriate to include tests to demonstrate the immunity
of RCD’s to transient disturbances such as those originating from switching
transients, including the interruption of inductive loads and relay contact
bounce etc. The IEC Basic EMC publication IEC 1000-4-4 includes tests for this
condition, establishing a common and reproducible basis for evaluating the performance
of equipment when subjected to repetitive fast transient bursts on supply, signal
and control ports.
It has been determined that for RCD’s, test level 4 is appropriate for common
mode testing, with a 5/50 nanosecond pulse having a voltage peak of 4kV and
a repetition rate of 2,5kHz.
Electrostatic Discharge Immunity Tests
IEC 1000-4-2 establishes a common and reproducible basis for evaluating the
performance of electrical and electronic equipment when subjected to electrostatic
discharges (ESD), including those which may occur from personnel to devices
such as RCD’s. For RCD’s, IEC 1543 requires IEC 1000-4-2 test level 3 which
specifies 6kV contact and 8kV air discharge. Contact discharge is applied to
conductive surfaces and air discharge at insulating surfaces.
It is important to note that in accordance with the requirements of IEC 1000-4-2,
the static electricity discharges are applied only
to such points and surfaces of the RCD (or any equipment), which are accessible
to personnel during normal usage.
Harmonics are sinusoidal voltages having frequencies that are whole multiples
of the frequency at which the supply system operates. Harmonic disturbances
are generally caused by equipment with non-linear voltage/current characteristics
or by periodic and line-synchronised switching of loads. As a result of cable
transfer capacitance, line inductance and connection of power factor correction
capacitors, parallel and series resonances may occur in the network and cause
a voltage amplification even at remote points from the distorting load. Summation
of the effects of harmonics are likely and must be considered.
The presence of harmonics in low voltage electrical supply systems has been
recognised for many years. It is however only in relatively recent times, that
the proliferation of harmonic producing devices has increased to the extent
that some serious attention needs to be given to the problem. Not generally
appreciated is the fact that household television receivers are one of the most
prolific generators of harmonics. A further irony is that energy efficient self
ballasted fluorescent lamps produce high levels of third harmonic currents.
For consumer generated harmonics, harmonic currents
predominate, and are aggravated in conditions where harmonic producing loads
are large in comparison to the supply capacity. It is unfortunate that users
are often misled by regulations that permit reduced sized neutral conductors.
The increased neutral currents that result directly from the presence of harmonics
should always be taken into account before any consideration is given to reduced
neutrals. In many applications it is becoming increasingly necessary to allow
for increased neutral currents and to overrate cables and switchgear accordingly.
The presence of power factor correction capacitors often aggravates the effects
of harmonics, which are generally observed in the form of overheating and data
corruption. Damage due to increased voltage stress is also becoming more common.
It is obvious that this paper in the main, has addressed the question of electromagnetic
compatibility in Residual Current Devices that are intended for Shock Hazard
and Fire Hazard protection. Most of the information presented is however generic,
and can be applied not only to the fixed low voltage installation, but also
to most equipment and appliances that are connected to the low voltage supply
system. The importance of understanding the implications of electromagnetic
interference and the need to consciously put in place programs that will reduce
the degree of electrical pollution that exists in our supply networks cannot
In developing societies such as South Africa with its massive electrification
program, the residential usage of electricity will become far greater as a percentage
of total electricity usage. The combined pressures of cost and appliance technology
are bound to ensure that whatever EMC problems already exist today, these can
only become worse. We all need to be proactive in dealing with EMC without introducing
the cost implications of over specification. We ignore EMC at our peril !
i) IEC 1543 -1995 RCD’s for household and similar
use - EMC
ii) IEC 1000-4-2 Electrostatic discharge immunity
iii) IEC 1000-4-3 Radiated, radio frequency, electromagnetic
field immunity test
iv) IEC 1000-4-4 Electric fast transient/burst immunity
v) IEC 1000-4-5 Surge immunity test
vi) IEC 1000-4-6 Immunity to conducted disturbances,
induced by radio frequency fields
vii) IEC document 77A/147A/CDV - Harmonics, Interharmonics
viii) NRS 048:1996 Draft 5 - Quality of Supply standards
ix) International standardisation in the field of
Electromagnetic Compatibility - by G Goldberg (Chairman ACEC of IEC)
x) ANSI/IEEE C62-41-1980 - IEEE guide for surge voltages
in low voltage a.c. power circuits
xi) The propagation and attenuation of surge voltages
and surge currents in low voltage a.c. circuits - by F D Martzloff
xii) Overvoltage coordination in l.v. electrical systems
- V Cohen
xiii)IEC 1008-1-1990 Residual current operated circuit
xiv) IEC 947-2 - 1995 - Circuit Breakers
xv) SAIEE workshop notice “EMC from DC to Light”Oct