IEC TR 60664-2-2:2002

TECHNICAL IEC
REPORT
TR 60664-2-2
First edition
2002-01
Insulation coordination for equipment
within low-voltage systems –
Part 2-2:
Interface considerations –
Application guide
Reference number
IEC/TR 60664-2-2:2002(E)
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TECHNICAL IEC
REPORT
TR 60664-2-2
First edition
2002-01
Insulation coordination for equipment
within low-voltage systems –
Part 2-2:
Interface considerations –
Application guide
 IEC 2002  Copyright - all rights reserved
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– 2 – TR 60664-2-2  IEC:2002(E)
CONTENTS
FOREWORD.3
INTRODUCTION.5
1 Scope.6
2 Reference documents.6
3 Definitions .7
4 Consideration of overvoltage categories .7
5 Consideration on the use of protective control .7
5.1 General .7
5.2 Recapitulation on lightning overvoltages.8
6 Observations on surge overvoltages and failure rates.9
6.1 General .9
6.2 Using field failure data.9
6.3 Preventing permanent damage.10
7 Principles of coordination between SPDs and with equipment to be protected
(refer also to IEC 61312-3) .11
8 Equipment for systems, installations and equipment operation under conditions
of inherent or protective control .11
8.1 Specific protection for sections of systems or installations.11
8.2 Specific protection within equipment.11
Bibliography.12

TR 60664-2-2  IEC:2002(E) – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INSULATION COORDINATION FOR EQUIPMENT
WITHIN LOW-VOLTAGE SYSTEMS –
Part 2-2: Interface considerations – Application guide
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of the IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, the IEC publishes International Standards. Their preparation is
entrusted to technical committees; any IEC National Committee interested in the subject dealt with may
participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. The IEC collaborates closely with the International
Organization for Standardization (ISO) in accordance with conditions determined by agreement between the
two organizations.
2) The formal decisions or agreements of the IEC on technical matters express, as nearly as possible, an
international consensus of opinion on the relevant subjects since each technical committee has representation
from all interested National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form
of standards, technical specifications, technical reports or guides and they are accepted by the National
Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this technical report may be the subject of
patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. However, a
technical committee may propose the publication of a technical report when it has collected
data of a different kind from that which is normally published as an International Standard, for
example “state of the art”.
Technical reports do not necessarily have to be reviewed until the data they provide are
considered to be no longer valid or useful by the maintenance team.
IEC 60664-2-2, which is a technical report, has been prepared by IEC technical committee 109:
Insulation coordination for low-voltage equipment.
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
28A/168/CDV 109/2/RVC
Full information on the voting for the approval of this technical report can be found in the
report on voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 3.
This document, which is purely informative, is not to be regarded as an International
Standard.
– 4 – TR 60664-2-2  IEC:2002(E)
The committee has decided that the contents of this publication will remain unchanged until 2004.
At this date, the publication will be
• reconfirmed,
• withdrawn;
• replaced by a revised edition,
• amended.
TR 60664-2-2  IEC:2002(E) – 5 –
INTRODUCTION
This technical report provides guidelines for a common basis for IEC technical committees
when considering interface issues in relation to insulation coordination. Surge protective
devices are key elements in achieving a controlled overvoltage condition in low-voltage a.c.
power systems and equipment. The aim of this guide is to avoid conflicting activities in the
various committees involved and to achieve consistent requirements and guidelines. It deals
with factors that influence the determination of overvoltage categories for installation and
equipment.
A technical report IEC TR 62066 is being prepared by a joint working group (JWG) initially
composed of representatives from the five IEC technical committees and subcommittees
listed below and subsequently complemented by experts appointed by national committees and
by CIGRE-CIRED.
SC 37A Low-voltage surge-protective devices
TC 64 Electrical installations and protection against electric shock
SC 77B High-frequency phenomena
TC 81 Lightning protection
TC 109 Insulation coordination for low-voltage equipment
Excerpts from IEC 62066 are included in order to identify information relevant to insulation
coordination for low-voltage equipment.

– 6 – TR 60664-2-2  IEC:2002(E)
INSULATION COORDINATION FOR EQUIPMENT
WITHIN LOW-VOLTAGE SYSTEMS –
Part 2-2: Interface considerations – Application guide
1 Scope
This technical report provides an overview of the different kinds of surge overvoltages that
can occur on low-voltage installations and equipment. In particular:
− the magnitude and duration of typical surges as well as their frequency of occurrence;
− information on overvoltages resulting from interaction between power and communication
systems;
− guidelines when considering interface issues in relation to insulation coordination;
− guidelines concerning surge protection means on the basis of availability and risk
considerations, including interaction within the system;
− highlights temporary overvoltages and other factors that have to be taken into account for
insulation coordination, primarily related to protective control using surge protective devices.
2 Reference documents
IEC 60364-4-44, Electrical installations of buildings – Part 4-44: Protection for safety –
Protection against voltage disturbances and electromagnetic disturbances
IEC 60664-1, Insulation coordination for equipment within low-voltage systems – Part 1:
Principles, requirements and tests
IEC 61000-4-5, Electromagnetic compatibility (EMC) – Part 4-5: Testing and measurement
techniques – Surge immunity test
IEC TS 61312-3, Protection against lightning electromagnetic impulse – Part 3: Requirements
of surge protective devices (SPDs)
IEC 61643-1, Surge protective devices connected to low-voltage power distribution systems –
Part 1: Performance requirements and testing methods
IEC TR 62066, General basic information regarding surge overvoltages and surge protection
in low-voltage a.c. power systems
IEC 61643-12, Surge protective devices connected to low-voltage power distribution systems –
Part 12: Selection and application principles
———————
To be published.
TR 60664-2-2  IEC:2002(E) – 7 –
3 Definitions
For the purpose of this technical report, the following definitions apply.
3.1
overvoltage category
numeral defining an transient overvoltage condition
(IEC 60664-1, 1.3.10)
3.2
controlled overvoltage condition
condition within an electrical system wherein the expected transient overvoltages are limited
to a defined level
(1.3.16 of IEC 60664-1)
3.3
inherent control
transient overvoltages limited by the electrical distribution system
3.4
protective control
transient overvoltages limited by devices such as surge protective devices (SPDs)
3.5
rated impulse voltage
impulse withstand voltage value assigned by the manufacturer to the equipment or a part of it,
characterizing the specified withstand capability of its insulation against transient overvoltages
(IEC 60664-1,1.3.9.2)
4 Consideration of overvoltage categories
Insulation coordination for equipment relies on a series of steps. The first step is to determine
the overvoltage category for the equipment (see IEC 60664-1, 2.2.2.1.1).
An overvoltage category is an indication of the degree of risk acceptable for the particular
application. The overvoltage category can be determined by either knowledge of the inherent
control or by use of protective control.
Protective control using SPDs could introduce an aspect of risk if the SPD fails or becomes
ineffective. There are methods to indicate failure of an SPD and methods to automatically
disconnect equipment from the supply system if it should fail. This latter method may be an
appropriate in certain applications (see IEC 61643-1 and IEC 61643-12).
Determination of the overvoltage category leads to the selection of the rated impulse voltage
using the tables in IEC 60664-1.
5 Consideration on the use of protective control
5.1 General
The installer will decide whether to provide protective control in an installation on the basis of
local information (good practice), regulation etc.

– 8 – TR 60664-2-2  IEC:2002(E)
Protective control of the equipment may be a decision taken either by the manufacturer or the user.
There are two significant elements in this decision-making process:
• the evaluation of the need for protective control, depending on the type of installation, the
type and purpose of equipment and an assessment of the risks;
• the evaluation of the level of protective control against overvoltages for an indirect
lightning strike. Overvoltages can be induced into the circuit
...