IEC 60305:2021

Insulators for overhead lines with a nominal voltage above 1000 V - Ceramic or glass insulator units for AC systems - Characteristics of insulator units of the cap and pin type

IEC 60305:2021 applies to string insulator units of the cap and pin type with insulating parts of ceramic material or glass, intended for AC overhead lines with a nominal voltage greater than 1 000 V and a frequency not greater than 100 Hz. It also applies to insulators of similar design used in substations. This document applies to string insulator units of the cap and pin type either with ball and socket couplings or with clevis and tongue couplings. This document applies to string insulator units for use on overhead lines in clean areas and polluted areas. For use in areas characterized by very heavy pollution levels and for other particular or extreme environmental conditions, it may be necessary for certain dimensions to be changed and insulator units having different creepage distances, spacing and forms may be preferred (for example, flat profile, hemispherical etc.). Insulators for use on DC systems may also need different dimensions. In any case, it is applicable that the standardized mechanical characteristics of this document and coupling sizes are retained. This fifth edition cancels and replaces the fourth edition published in 1995. This edition includes the following significant technical changes with respect to the previous edition:
- wording in Scope changed from "it is recommended" to "it is applicable";
- new normative references added;
- electromechanical or mechanical failing load in Clause 4 specified;
- new figures added showing profiles.

Isolateurs pour lignes aériennes de tension nominale supérieure à 1000 V - Eléments d'isolateurs en céramique ou en verre pour réseaux à tension alternative - Caractéristiques des éléments d'isolateurs du type capot et tige

L'IEC 60305:2021 s'applique aux éléments de chaînes d'isolateurs du type à capot et tige ayant des parties isolantes en matière céramique ou en verre et destinés aux lignes aériennes fonctionnant en courant alternatif à une tension nominale supérieure à 1 000 V et à une fréquence au plus égale à 100 Hz. Elle s'applique également aux isolateurs du même type utilisés dans les postes. Le présent document s'applique aux éléments de chaînes d'isolateurs du type à capot et tige soit avec assemblage à rotule, soit avec assemblage à chape et tenon. Le présent document s'applique aux éléments de chaînes d'isolateurs destinés aux lignes aériennes situées dans des régions polluées et non polluées. Pour les isolateurs destinés à être utilisés dans des régions très fortement polluées et dans d'autres conditions environnementales particulières ou extrêmes, il peut être nécessaire de modifier certaines dimensions et il peut être préférable d'utiliser des éléments d'isolateurs ayant des lignes de fuite, des pas et des formes différentes (par exemple, profil plat, hémisphérique, etc.). Les isolateurs destinés à être utilisés sur les réseaux à tension continue peuvent également nécessiter des dimensions différentes. Dans tous les cas, il est possible de retenir les caractéristiques mécaniques normalisées du présent document et les dimensions d'assemblage. Cette cinquième édition annule et remplace la quatrième édition parue en 1995. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
- reformulation du domaine d'application: "il est recommandé d’utiliser" a été remplacé par "il est possible de retenir";
- ajout de nouvelles références normatives;
- spécification à l'Article 4 de la charge de rupture électromécanique ou mécanique;
- ajout de nouvelles figures représentant des profils.

General Information

• Status: Published
• Publication Date: 10-Jan-2021
• ICS: 29.080.10 - Insulators
• ICS: 29.240.20 - Power transmission and distribution lines
• Technical Committee: TC 36 - Insulators
• Drafting Committee: MT 17 - TC 36/MT 17
• Current Stage: PPUB - Publication issued
• Start Date: 11-Jan-2021
• Completion Date: 20-Jan-2021

Overview

IEC 60305:2021 - published by the International Electrotechnical Commission (IEC) - specifies the mechanical and dimensional characteristics for cap-and-pin string insulator units with insulating parts made of ceramic or glass, intended for AC overhead lines with a nominal voltage above 1 000 V and frequency up to 100 Hz. The standard covers units with ball-and-socket or clevis-and-tongue couplings, and applies to use in both clean and polluted areas (with guidance where very heavy pollution or DC service may require different dimensions).

This fifth edition updates terminology in the Scope, adds normative references, specifies electromechanical/mechanical failing load requirements, and adds new profile figures and expanded tables.

Key topics and technical requirements

• Scope limits: AC systems, nominal voltage > 1 000 V, frequency ≤ 100 Hz; also applicable to similar substation insulators.
• Standardized characteristics (specified in the tables):
  • Specified electromechanical or mechanical failing load (SFL) (per IEC 60383-1)
  • Maximum nominal diameter of insulating parts
  • Nominal spacing
  • Minimum nominal creepage distance
  • Standard coupling type and dimensions
• Profiles and shed shapes: standard, anti‑fog (P), aerodynamic (D), two‑alternating (V), three‑alternating (T) - figures and designations are provided.
• Designation & marking: format uses letter U + SFL (kN) + coupling letter (B = ball/socket, C = clevis/tongue) and suffixes for spacing (S/L), pollution (P), or profile (P/D/V/T). Example: U160 BS.
• Tolerances: nominal spacing tolerance = ±(0.03·P + 0.3) mm (P in mm); other tolerances per IEC 60383-1.
• Notes on polluted areas: creepage distance effectiveness varies with shed shape and diameter; heavy pollution or DC service may require alternate geometries while retaining standardized mechanical/coupling sizes.

Applications and practical value

• Ensures interchangeability and mechanical compatibility of string insulator units used on transmission lines and in substations.
• Used by:
  • Transmission/distribution utilities specifying insulators for overhead lines
  • Insulator manufacturers designing cap-and-pin ceramic/glass units
  • Procurement and testing laboratories verifying dimensional and mechanical compliance
  • Consulting engineers selecting insulator strings for polluted environments or special profiles
• Practical outcomes: consistent coupling sizes, predictable mechanical performance (SFL), and clear labelling for procurement and asset management.

Related standards

• IEC 60383-1 - electrical definitions, test methods and acceptance criteria for string insulator units
• IEC 60120 - ball-and-socket coupling dimensions
• IEC 60471 - clevis and tongue coupling dimensions
• IEC 815 and IEC TS 60815-1 - guidance on pollution levels and site pollution severity

Keywords: IEC 60305:2021, insulators for overhead lines, cap and pin type, ceramic insulator units, glass insulator units, string insulator units, creepage distance, nominal spacing, electromechanical failing load, ball and socket coupling, clevis and tongue coupling.

Standards Content (Sample)

IEC 60305 ®
Edition 5.0 2021-01
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Insulators for overhead lines with a nominal voltage above 1 000 V – Ceramic or
glass insulator units for AC systems – Characteristics of insulator units of the
cap and pin type
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IEC 60305 ®
Edition 5.0 2021-01
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Insulators for overhead lines with a nominal voltage above 1 000 V – Ceramic or

glass insulator units for AC systems – Characteristics of insulator units of the

cap and pin type
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.080.10; 29.240.20 ISBN 978-2-8322-9270-9

– 2 – IEC 60305:2021 RLV © IEC 2021
CONTENTS
FOREWORD . 3
1 Scope and object . 5
2 Normative references . 5
3 Terms and definitions . 6
4 Mechanical and dimensional characteristics, dimensions and types . 6
5 Designation and marking with respect to shed profile . 6
6 Tolerances . 8
Bibliography . 16

Figure 1 – String insulator unit with ball and socket coupling .
Figure 2 – String insulator unit with clevis and tongue couplings .
Figure 1 – Typical "standard" profile . 7
Figure 2 – Typical "anti-fog" profile "P" . 7
Figure 3 – Typical "aerodynamic" profile "D" . 7
Figure 4 – Typical "two-alternating" profile "V" . 7
Figure 5 – Typical "three-alternating" profile "T" . 8
Figure 6 – String insulator unit of standard and anti-fog profile with ball and socket
coupling . 10
Figure 7 – String insulator unit of standard and anti-fog profile with clevis and tongue
coupling . 12
Figure 8 – String insulator unit of aerodynamic profile with ball and socket coupling . 13
Figure 9 – String insulator unit of two-alternating profile with ball and socket coupling . 13
Figure 10 – String insulator unit of three-alternating profile with ball and socket
coupling . 14

Table 1 – Specified values of mechanical and dimensional characteristics for string
insulator units with ball and socket couplings .
Table 2 – Specified values of mechanical and dimensional characteristics for string
insulator units with clevis and tongue couplings .
Table 1 – Specified values of mechanical and dimensional characteristics for string
insulator units of standard and anti-fog profile with ball and socket couplings . 11
Table 2 – Specified values of mechanical and dimensional characteristics for string
insulator units of standard and anti-fog profile with clevis and tongue couplings . 12
Table 3 – Specified values of mechanical and dimensional characteristics for string
insulator units of aerodynamic profile with ball and socket couplings . 13
Table 4 – Specified values of mechanical and dimensional characteristics for string
insulator units of two-alternating profile with ball and socket couplings . 14
Table 5 – Specified values of mechanical and dimensional characteristics for string
insulator units of three-alternating profile with ball and socket couplings . 15

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INSULATORS FOR OVERHEAD LINES WITH
A NOMINAL VOLTAGE ABOVE 1 000 V –
CERAMIC OR GLASS INSULATOR UNITS FOR AC SYSTEMS –
CHARACTERISTICS OF INSULATOR UNITS OF THE CAP AND PIN TYPE

FOREWORD
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This redline version of the official IEC Standard allows the user to identify the changes
made to the previous edition IEC 60305:1995. A vertical bar appears in the margin
wherever a change has been made. Additions are in green text, deletions are in
strikethrough red text.
– 4 – IEC 60305:2021 RLV © IEC 2021
International Standard IEC 60305 has been prepared by IEC technical committee 36:
Insulators.
This fifth edition cancels and replaces the fourth edition published in 1995. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) wording in Scope changed from "it is recommended" to "it is applicable";
b) new normative references added;
c) electromechanical or mechanical failing load in Clause 4 specified;
d) new figures added showing profiles;
e) Tables 1, 2, 3, 4 and 5 expanded to include more specified values.
The text of this International Standard is based on the following documents:
FDIS Report on voting
36/499/FDIS 36/501/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.
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.
INSULATORS FOR OVERHEAD LINES WITH
A NOMINAL VOLTAGE ABOVE 1 000 V –
CERAMIC OR GLASS INSULATOR UNITS FOR AC SYSTEMS –
CHARACTERISTICS OF INSULATOR UNITS OF THE CAP AND PIN TYPE

1 Scope and object
This International Standard applies to string insulator units of the cap and pin type with
insulating parts of ceramic material or glass, intended for AC overhead lines with a nominal
voltage greater than 1 000 V and a frequency not greater than 100 Hz. It also applies to
insulators of similar design used in substations.
This document applies to string insulator units of the cap and pin type either with ball and
socket couplings or with clevis and tongue couplings.
This document applies to string insulator units for use on overhead lines in clean areas and
polluted areas. For use in areas characterized by very heavy pollution levels and for other
particular or extreme environmental conditions, it may be necessary for certain dimensions to
be changed and insulator units having different creepage distances, spacing and forms may
be preferred (for example, flat profile, hemispherical etc.). Insulators for use on DC systems
may also need different dimensions. In any case, it is recommended applicable that the
standardized mechanical characteristics of this document and coupling sizes are retained.
The object of this document is to prescribe specified values for the mechanical characteristics
and for the main dimensions of string insulator units of the cap and pin type.
The power frequency, lightning impulse and puncture withstand voltages of string insulator
units are not specified in this document. IEC 60383-1 gives the electrical characteristics which
define string insulator units; their values shall be are agreed between purchaser and
manufacturer.
Ball and socket couplings are covered by IEC 60120, clevis and tongue couplings by
IEC 60471.
NOTE For the definition of pollution levels see IEC 815. For the definition of site pollution severity see IEC TS
60815-1.
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 60383-1: 1993, Insulators for overhead lines with a nominal voltage above 1000 V – Part
1: Ceramic or glass insulator units for AC systems – Definitions, test methods and acceptance
criteria
IEC 471: 1977, Dimensions of clevis and tongue couplings of string insulator units
IEC 815: 1986, Guide for the selection of insulators in respect of polluted conditions

– 6 – IEC 60305:2021 RLV © IEC 2021
3 Terms and definitions
No terms and definitions are listed in this document.
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
4 Mechanical and dimensional characteristics, dimensions and types
String insulator units of the cap and pin type are standardized by the following specified
characteristics:
– Specified electromechanical or mechanical failing load (SFL) according to IEC 60383-1;
– maximum nominal diameter of the insulating part;
– nominal spacing;
– minimum nominal creepage distance;
– standard coupling.
The corresponding values are indicated in Table 1, Table 2, Table 3, Table 4 and Table 5.
NOTE 1 The following points merit attention for insulators for use in polluted areas:
a) even if the creepage distance is the same, the withstand voltage characteristics may change with shed shape of
the insulators;
b) even if the string length is the same, the withstand voltage characteristics may decrease with increasing
insulator strength due to the lower efficiency of creepage distance for a larger average diameter.
NOTE 2 IEC 60815 gives details on the important parameters of shed profiles for antipollution insulators.
5 Designation and marking with respect to shed profile
Insulators are designated in Table 1, Table 2, Table 3, Table 4 and Table 5 by the letter U
followed by a number indicating the specified electromechanical or mechanical failing load in
kilonewtons.
The letter B or C which follows specifies a ball and socket or clevis and tongue, respectively.
The following letter S or L, if present, specifies a short or long spacing.
Long creepage distance insulators for polluted areas are designated by a final letter P.
The letter P, D, V, or T present for "anti-fog" profile, "aerodynamic" profile, "two-alternating"
profile, or "three-alternating" profile, as shown in Figure 1, Figure 2, Figure 3,Figure 4 and
Figure 5, respectively.
IEC 60383-1 specifies that insulators shall be marked with the specified electromechanical or
mechanical failing load. This load may be indicated by using the first part of the designation
given in the first column of Table 1, Table 2, Table 3, Table 4 and Table 5: For instance, the
insulator may be marked U 160 for the units U 160 BS, U 160 BL and U 160 BLP.

Figure 1 – Typical "standard" profile

Figure 2 – Typical "anti-fog" profile "P"

Figure 3 – Typical "aerodynamic" profile "D"

Figure 4 – Typical "two-alternating" profile "V"

– 8 – IEC 60305:2021 RLV © IEC 2021

Figure 5 – Typical "three-alternating" profile "T"
6 Tolerances
Except for nominal spacing, tolerances for dimensions indicated in IEC 60383-1 are
applicable to all nominal values including maximum nominal diameter and minimum nominal
creepage distance values given in Table 1, Table 2, Table 3, Table 4 and Table 5.
Diagram of Table 1, Table 2, Table 3, Table 4 and Table 5 is shown in Figure 6, Figure 7,
Figure 8, Figure 9 and Figure 10, respectively.
Nominal spacing tolerance shall be:
± (0,03 P + 0,3) mm
P being spacing expressed in millimetres.

P
d1
D
CEI-IEC  1 048/95
Figure 1 – String insulator unit with ball and socket coupling

Table 1 – Specified values of mechanical and dimensional characteristics
for string insulator units with ball and socket couplings

Electromechanical Maximum nominal Nominal Minimum nominal Standard coupling
Designation or mechanical diameter of the spacing creepage distance according to
failing load insulating part  IEC 120
D P mm
kN mm mm d1
U 40 B 40 175 110 190 11
U 40 BP 40 210 110 295 11
U 70 BS 70 255 127 295 16
U 70 BL 70 255 146 295 16
U 70 BLP 70 280 146 440 16
U 100 BS 100 255 127 295 16
U 100 BL 100 255 146 295 16
U 100 BLP 100 280 146 440 16
U 120 B 120 255 146 295 16
U 120 BP 120 280 146 440 16
U 160 BS 160 280 146 315 20
U 160 BSP 160 330 146 440 20
U 160 BL 160 280 170 340 20
U 160 BLP 160 330 170 525 20
U 210 B 210 300 170 370 20
U 210 BP 210 330 170 525 20
U 300 B 300 330 195 390 24
U 300 BP 300 400 195 590 24
U 400 B 400 380 205 525 28
U 530 B 530 380 240 600 32
P
D
CEI-IEC  1 049/95
Figure 2 – String insulator unit with clevis and tongue couplings

– 10 – IEC 60305:2021 RLV © IEC 2021
Table 2 – Specified values of mechanical and dimensional characteristics
for string insulator units with clevis and tongue couplings

Electromechanical Maximum nominal Nominal spacing Minimum nominal Standard coupling
Designation or mechanical diameter of the creepage according to
failing load insulating part   distance IEC 471
D P
kN mm mm mm
U 70 C 70 255 146 295 16 C
U 70 CP 70 280 146 440 16 C
U 100 C 100 255 146 295 16 C
U 100 CP 100 280 146 440 16 C
U 120 C 120 255 146 295 16 C
U 120 CP 120 280 146 440 16 C
U 160 C 160 280 170 340 19 C
U 160 CP 160 330 170 525 19 C
U 210 C 210 300 178 370 22 C
U 210 CP 210 330 178 525 22 C
NOTE – Insulators having an electromechanical or mechanical failing load exceeding 210 kN are not specified.
If necessary, the insulators with ball and socket coupling defined in table 1 shall preferably be used.

Figure 6 – String insulator unit of standard and anti-fog
profile with ball and socket coupling

Table 1 – Specified values of mechanical and dimensional characteristics for string
insulator units of standard and anti-fog profile with ball and socket couplings
Designation Specified Maximum Nominal Minimum Standard
electromechanical nominal spacing nominal coupling
or mechanical diameter of the creepage according to
failing load insulating part distance IEC 60120

kN D P mm d1
mm mm
U 40 B 40 175 110 190 11
U 40 BP 40 210 110 295 11
U 70 BS 70 255 127 295 16
U 70 BL 70 255 146 295 16
U 70 BLP 70 280 146 440 16
U 100 BS 100 255 127 295 16
U 100 BL 100 255 146 295 16
U 100 BLP 100 280 146 440 16
U 120 B 120 255 146 295 16
U 120 BP 120 280 146 440 16
U 160 BS 160 280 146 315 20
U 160 BSP 160 330 146 440 20
U 160 BL 160 280 170 340 20
U 160 BLP 160 330 170 525 20
U 210 B 210 300 170 370 20
U 210 BP 210 330 170 525 20
U 300 B 300 330 195 390 24
U 300 BP 300 400 195 590 24
U 400 B 400 380 205 525 28
U 420 B 420 380 205 525 28
U 530 B 530 380 240 600 32
U 550 B 550 380 240 600 32
U 700 B 700 430 280 600 36
U 840 B 840 430 300 600 40
– 12 – IEC 60305:2021 RLV © IEC 2021

Figure 7 – String insulator unit of standard and anti-fog profile
with clevis and tongue coupling
Table 2 – Specified values of mechanical and dimensional characteristics for string
insulator units of standard and anti-fog profile with clevis and tongue couplings
Designation Specified Maximum Nominal Minimum Standard
electromechanical nominal spacing nominal coupling
or mechanical diameter of the creepage according to
failing load insulating part distance IEC 60471

kN D P mm
mm mm
U 40 C 40 190 140 200 16 C
U 70 C 70 255 146 295 16 C
U 70 CP 70 280 146 440 16 C
U 100 C 100 255 146 295 16 C
U 100 CP 100 280 146 440 16 C
U 120 C 120 255 146 295 16 C
U 120 CP 120 280 146 440 16 C
U 160 C 160 280 170 340 19 C
U 160 CP 160 330 170 525 19 C
U 210 C 210 300 178 370 22 C
U 210 CP 210 330 178 525 22 C
NOTE Insulators having an electromechanical or mechanical failing load exceeding 210 kN are not specified. If
necessary, the insulators with ball and socket coupling defined in Table 1 shall preferably be used.

Figure 8 – String insulator unit of aerodynamic profile with ball and socket coupling
Table 3 – Specified values of mechanical and dimensional characteristics for string
insulator units of aerodynamic profile with ball and socket couplings
Designation Specified Maximum Nominal Minimum Standard
electromechanical nominal spacing nominal coupling
or mechanical diameter of the creepage according to
failing load insulating part distance IEC 60120

kN D P
mm mm mm
U 70 BSD 70 380 127 305 16
U 70 BLD 70 380 146 305 16
U 120 BSD 120 380 127 295 16
U 120 BLD 120 380 146 295 16
U 160 BD 160 425 146 375 20
U 210 BD 210 425 170 375 20
Figure 9 – String insulator unit of two-alternating profile with ball and socket coupling

– 14 – IEC 60305:2021 RLV © IEC 2021
Table 4 – Specified values of mechanical and dimensional characteristics for string
insulator units of two-alternating profile with ball and socket couplings
Designation Specified Maximum Nominal Minimum Standard
electromechanical nominal spacing nominal coupling
or mechanical diameter of the creepage according to
failing load insulating part distance IEC 60120

kN D P
mm mm mm
U 70 BSV 70 280 146 450 16
U 70 BLV 70 280 160 450 16
U 120 BSV 120 280 146 450 16
U 120 BLV 120 280 160 450 16
U 160 BSV 160 290 155 450 20
U 160 BV 160 290 160 450 20
U 160 BLV 160 355 170 450 20
U 210 BV 210 355 170 450 20
U 240 BV 240 300 170 450 24
U 300 BV 300 360 195 485 24
U 400 BV 400 400 205 555 28
U 420 BV 420 400 205 555 28
U 530 BV 530 420 240 600 32
U 550 BV 550 420 240 600 32
Figure 10 – String insulator unit of three-alternating
profile with ball and socket coupling

Table 5 – Specified values of mechanical and dimensional characteristics for string
insulator units of three-alternating profile with ball and socket couplings
Designation Specified Maximum Nominal Minimum Standard
electromechanical nominal spacing nominal coupling
or mechanical diameter of the creepage according to
failing load insulating part distance IEC 60120

kN D P
mm mm mm
U 70 BT 70 320 155 550 16
U 120 BT 120 320 155 550 16
U 160 BST 160 325 155 545 20
U 160 BT 160 325 160 545 20
U 160 BLT 160 325 170 545 20
U 210 BT 210 325 170 545 20
U 240 BT 240 325 170 545 24
U 300 BT 300 400 195 550 24
U 400 BT 400 400 205 635 28
U 420 BT 420 400 205 635 28
U 530 BT 530 400 240 635 32
U 550 BT 550 400 240 635 32
– 16 – IEC 60305:2021 RLV © IEC 2021
Bibliography
[1] IEC 60120:2020, Ball and socket couplings of string insulator units – Dimensions
[2] IEC 60471:2020, Clevis and tongue couplings of string insulator units – Dimensions
[3] IEC TS 60815-1:2008, Selection and dimensioning of high-voltage insulators intended
for use in polluted conditions – Part 1: Definitions, information and general principles
[4] IEC TS 60815-2:2008, Selection and dimensioning of high-voltage insulators intended
for use in polluted conditions – Part 2: Ceramic and glass insulators for AC systems

_____________
IEC 60305 ®
Edition 5.0 2021-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Insulators for overhead lines with a nominal voltage above 1 000 V – Ceramic or
glass insulator units for AC systems – Characteristics of insulator units of the
cap and pin type
Isolateurs pour lignes aériennes de tension nominale supérieure a 1 000 V –
Éléments d’isolateurs en céramique ou en verre pour réseaux à tension
alternative – Caractéristiques des éléments d'isolateurs du type capot et tige

– 2 – IEC 60305:2021 © IEC 2021
CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Mechanical characteristics, dimensions and types . 6
5 Designation and marking with respect to shed profile . 6
6 Tolerances . 8
Bibliography . 14

Figure 1 – Typical "standard" profile . 7
Figure 2 – Typical "anti-fog" profile "P" . 7
Figure 3 – Typical "aerodynamic" profile "D" . 7
Figure 4 – Typical "two-alternating" profile "V" . 7
Figure 5 – Typical "three-alternating" profile "T" . 8
Figure 6 – String insulator unit of standard and anti-fog profile with ball and socket
coupling . 8
Figure 7 – String insulator unit of standard and anti-fog profile with clevis and tongue
coupling . 10
Figure 8 – String insulator unit of aerodynamic profile with ball and socket coupling . 11
Figure 9 – String insulator unit of two-alternating profile with ball and socket coupling . 11
Figure 10 – String insulator unit of three-alternating profile with ball and socket
coupling . 12

Table 1 – Specified values of mechanical and dimensional characteristics for string
insulator units of standard and anti-fog profile with ball and socket couplings . 9
Table 2 – Specified values of mechanical and dimensional characteristics for string
insulator units of standard and anti-fog profile with clevis and tongue couplings . 10
Table 3 – Specified values of mechanical and dimensional characteristics for string
insulator units of aerodynamic profile with ball and socket couplings . 11
Table 4 – Specified values of mechanical and dimensional characteristics for string
insulator units of two-alternating profile with ball and socket couplings . 12
Table 5 – Specified values of mechanical and dimensional characteristics for string
insulator units of three-alternating profile with ball and socket couplings . 13

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INSULATORS FOR OVERHEAD LINES WITH
A NOMINAL VOLTAGE ABOVE 1 000 V –
CERAMIC OR GLASS INSULATOR UNITS FOR AC SYSTEMS –
CHARACTERISTICS OF INSULATOR UNITS OF THE CAP AND PIN TYPE

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of 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, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as "IEC
Publication(s)"). 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. 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 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 IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60305 has been prepared by IEC technical committee 36:
Insulators.
This fifth edition cancels and replaces the fourth edition published in 1995. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) wording in Scope changed from "it is recommended" to "it is applicable";
b) new normative references added;
c) electromechanical or mechanical failing load in Clause 4 specified;
d) new figures added showing profiles;
e) Tables 1, 2, 3, 4 and 5 expanded to include more specified values.

– 4 – IEC 60305:2021 © IEC 2021
The text of this International Standard is based on the following documents:
FDIS Report on voting
36/499/FDIS 36/501/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.
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.
INSULATORS FOR OVERHEAD LINES WITH
A NOMINAL VOLTAGE ABOVE 1 000 V –
CERAMIC OR GLASS INSULATOR UNITS FOR AC SYSTEMS –
CHARACTERISTICS OF INSULATOR UNITS OF THE CAP AND PIN TYPE

1 Scope
This International Standard applies to string insulator units of the cap and pin type with
insulating parts of ceramic material or glass, intended for AC overhead lines with a nominal
voltage greater than 1 000 V and a frequency not greater than 100 Hz. It also applies to
insulators of similar design used in substations.
This document applies to string insulator units of the cap and pin type either with ball and
socket couplings or with clevis and tongue couplings.
This document applies to string insulator units for use on overhead lines in clean areas and
polluted areas. For use in areas characterized by very heavy pollution levels and for other
particular or extreme environmental conditions, it may be necessary for certain dimensions to
be changed and insulator units having different creepage distances, spacing and forms may
be preferred (for example, flat profile, hemispherical etc.). Insulators for use on DC systems
may also need different dimensions. In any case, it is applicable that the standardized
mechanical characteristics of this document and coupling sizes are retained.
The object of this document is to prescribe specified values for the mechanical characteristics
and for the main dimensions of string insulator units of the cap and pin type.
The power frequency, lightning impulse and puncture withstand voltages of string insulator
units are not specified in this document. IEC 60383-1 gives the electrical characteristics which
define string insulator units; their values are agreed between purchaser and manufacturer.
Ball and socket couplings are covered by IEC 60120, clevis and tongue couplings by
IEC 60471.
NOTE For the definition of site pollution severity see IEC TS 60815-1.
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 60383-1, Insulators for overhead lines with a nominal voltage above 1000 V – Part 1:
Ceramic or glass insulator units for AC systems – Definitions, test methods and acceptance
criteria
3 Terms and definitions
No terms and definitions are listed in this document.

– 6 – IEC 60305:2021 © IEC 2021
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
4 Mechanical characteristics, dimensions and types
String insulator units of the cap and pin type are standardized by the following specified
characteristics:
– Specified electromechanical or mechanical failing load (SFL) according to IEC 60383-1;
– maximum nominal diameter of the insulating part;
– nominal spacing;
– minimum nominal creepage distance;
– standard coupling.
The corresponding values are indicated in Table 1, Table 2, Table 3, Table 4 and Table 5.
NOTE 1 The following points merit attention for insulators for use in polluted areas:
a) even if the creepage distance is the same, the withstand voltage characteristics may change with shed shape of
the insulators;
b) even if the string length is the same, the withstand voltage characteristics may decrease with increasing
insulator strength due to the lower efficiency of creepage distance for a larger average diameter.
NOTE 2 IEC 60815 gives details on the important parameters of shed profiles for antipollution insulators.
5 Designation and marking with respect to shed profile
Insulators are designated in Table 1, Table 2, Table 3, Table 4 and Table 5 by the letter U
followed by a number indicating the specified electromechanical or mechanical failing load in
kilonewtons.
The letter B or C which follows specifies a ball and socket or clevis and tongue, respectively.
The following letter S or L, if present, specifies a short or long spacing.
The letter P, D, V, or T present for "anti-fog" profile, "aerodynamic" profile, "two-alternating"
profile, or "three-alternating" profile, as shown in Figure 1, Figure 2, Figure 3,Figure 4 and
Figure 5, respectively.
IEC 60383-1 specifies that insulators shall be marked with the specified electromechanical or
mechanical failing load. This load may be indicated by using the first part of the designation
given in the first column of Table 1, Table 2, Table 3, Table 4 and Table 5: For instance, the
insulator may be marked U 160 for the units U 160 BS, U 160 BL and U 160 BLP.

Figure 1 – Typical "standard" profile

Figure 2 – Typical "anti-fog" profile "P"

Figure 3 – Typical "aerodynamic" profile "D"

Figure 4 – Typical "two-alternating" profile "V"

– 8 – IEC 60305:2021 © IEC 2021

Figure 5 – Typical "three-alternating" profile "T"
6 Tolerances
Except for nominal spacing, tolerances for dimensions indicated in IEC 60383-1 are
applicable to all nominal values including maximum nominal diameter and minimum nominal
creepage distance values given in Table 1, Table 2, Table 3, Table 4 and Table 5.
Diagram of Table 1, Table 2, Table 3, Table 4 and Table 5 is shown in Figure 6, Figure 7,
Figure 8, Figure 9 and Figure 10, respectively.
Nominal spacing tolerance shall be:
± (0,03 P + 0,3) mm
P being spacing expressed in millimetres.

Figure 6 – String insulator unit of standard and anti-fog
profile with ball and socket coupling

Table 1 – Specified values of mechanical and dimensional characteristics for string
insulator units of standard and anti-fog profile with ball and socket couplings
Designation Specified Maximum Nominal Minimum Standard
electromechanical nominal spacing nominal coupling
or mechanical diameter of the creepage according to
failing load insulating part distance IEC 60120

kN D P mm d1
mm mm
U 40 B 40 175 110 190 11
U 40 BP 40 210 110 295 11
U 70 BS 70 255 127 295 16
U 70 BL 70 255 146 295 16
U 70 BLP 70 280 146 440 16
U 100 BS 100 255 127 295 16
U 100 BL 100 255 146 295 16
U 100 BLP 100 280 146 440 16
U 120 B 120 255 146 295 16
U 120 BP 120 280 146 440 16
U 160 BS 160 280 146 315 20
U 160 BSP 160 330 146 440 20
U 160 BL 160 280 170 340 20
U 160 BLP 160 330 170 525 20
U 210 B 210 300 170 370 20
U 210 BP 210 330 170 525 20
U 300 B 300 330 195 390 24
U 300 BP 300 400 195 590 24
U 400 B 400 380 205 525 28
U 420 B 420 380 205 525 28
U 530 B 530 380 240 600 32
U 550 B 550 380 240 600 32
U 700 B 700 430 280 600 36
U 840 B 840 430 300 600 40
– 10 – IEC 60305:2021 © IEC 2021

Figure 7 – String insulator unit of standard and anti-fog profile
with clevis and tongue coupling
Table 2 – Specified values of mechanical and dimensional characteristics for string
insulator units of standard and anti-fog profile with clevis and tongue couplings
Designation Specified Maximum Nominal Minimum Standard
electromechanical nominal spacing nominal coupling
or mechanical diameter of the creepage according to
failing load insulating part distance IEC 60471

kN D P mm
mm mm
U 40 C 40 190 140 200 16 C
U 70 C 70 255 146 295 16 C
U 70 CP 70 280 146 440 16 C
U 100 C 100 255 146 295 16 C
U 100 CP 100 280 146 440 16 C
U 120 C 120 255 146 295 16 C
U 120 CP 120 280 146 440 16 C
U 160 C 160 280 170 340 19 C
U 160 CP 160 330 170 525 19 C
U 210 C 210
...

IEC 60305 ®
Edition 5.0 2021-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Insulators for overhead lines with a nominal voltage above 1 000 V – Ceramic or
glass insulator units for AC systems – Characteristics of insulator units of the
cap and pin type
Isolateurs pour lignes aériennes de tension nominale supérieure a 1 000 V –
Éléments d’isolateurs en céramique ou en verre pour réseaux à tension
alternative – Caractéristiques des éléments d'isolateurs du type capot et tige

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IEC 60305 ®
Edition 5.0 2021-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Insulators for overhead lines with a nominal voltage above 1 000 V – Ceramic or

glass insulator units for AC systems – Characteristics of insulator units of the

cap and pin type
Isolateurs pour lignes aériennes de tension nominale supérieure a 1 000 V –

Éléments d’isolateurs en céramique ou en verre pour réseaux à tension

alternative – Caractéristiques des éléments d'isolateurs du type capot et tige

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.080.10; 29.240.20 ISBN 978-2-8322-9203-7

– 2 – IEC 60305:2021 © IEC 2021
CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Mechanical characteristics, dimensions and types . 6
5 Designation and marking with respect to shed profile . 6
6 Tolerances . 8
Bibliography . 14

Figure 1 – Typical "standard" profile . 7
Figure 2 – Typical "anti-fog" profile "P" . 7
Figure 3 – Typical "aerodynamic" profile "D" . 7
Figure 4 – Typical "two-alternating" profile "V" . 7
Figure 5 – Typical "three-alternating" profile "T" . 8
Figure 6 – String insulator unit of standard and anti-fog profile with ball and socket
coupling . 8
Figure 7 – String insulator unit of standard and anti-fog profile with clevis and tongue
coupling . 10
Figure 8 – String insulator unit of aerodynamic profile with ball and socket coupling . 11
Figure 9 – String insulator unit of two-alternating profile with ball and socket coupling . 11
Figure 10 – String insulator unit of three-alternating profile with ball and socket
coupling . 12

Table 1 – Specified values of mechanical and dimensional characteristics for string
insulator units of standard and anti-fog profile with ball and socket couplings . 9
Table 2 – Specified values of mechanical and dimensional characteristics for string
insulator units of standard and anti-fog profile with clevis and tongue couplings . 10
Table 3 – Specified values of mechanical and dimensional characteristics for string
insulator units of aerodynamic profile with ball and socket couplings . 11
Table 4 – Specified values of mechanical and dimensional characteristics for string
insulator units of two-alternating profile with ball and socket couplings . 12
Table 5 – Specified values of mechanical and dimensional characteristics for string
insulator units of three-alternating profile with ball and socket couplings . 13

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INSULATORS FOR OVERHEAD LINES WITH
A NOMINAL VOLTAGE ABOVE 1 000 V –
CERAMIC OR GLASS INSULATOR UNITS FOR AC SYSTEMS –
CHARACTERISTICS OF INSULATOR UNITS OF THE CAP AND PIN TYPE

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of 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, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as "IEC
Publication(s)"). 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. 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 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 IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60305 has been prepared by IEC technical committee 36:
Insulators.
This fifth edition cancels and replaces the fourth edition published in 1995. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) wording in Scope changed from "it is recommended" to "it is applicable";
b) new normative references added;
c) electromechanical or mechanical failing load in Clause 4 specified;
d) new figures added showing profiles;
e) Tables 1, 2, 3, 4 and 5 expanded to include more specified values.

– 4 – IEC 60305:2021 © IEC 2021
The text of this International Standard is based on the following documents:
FDIS Report on voting
36/499/FDIS 36/501/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.
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.
INSULATORS FOR OVERHEAD LINES WITH
A NOMINAL VOLTAGE ABOVE 1 000 V –
CERAMIC OR GLASS INSULATOR UNITS FOR AC SYSTEMS –
CHARACTERISTICS OF INSULATOR UNITS OF THE CAP AND PIN TYPE

1 Scope
This International Standard applies to string insulator units of the cap and pin type with
insulating parts of ceramic material or glass, intended for AC overhead lines with a nominal
voltage greater than 1 000 V and a frequency not greater than 100 Hz. It also applies to
insulators of similar design used in substations.
This document applies to string insulator units of the cap and pin type either with ball and
socket couplings or with clevis and tongue couplings.
This document applies to string insulator units for use on overhead lines in clean areas and
polluted areas. For use in areas characterized by very heavy pollution levels and for other
particular or extreme environmental conditions, it may be necessary for certain dimensions to
be changed and insulator units having different creepage distances, spacing and forms may
be preferred (for example, flat profile, hemispherical etc.). Insulators for use on DC systems
may also need different dimensions. In any case, it is applicable that the standardized
mechanical characteristics of this document and coupling sizes are retained.
The object of this document is to prescribe specified values for the mechanical characteristics
and for the main dimensions of string insulator units of the cap and pin type.
The power frequency, lightning impulse and puncture withstand voltages of string insulator
units are not specified in this document. IEC 60383-1 gives the electrical characteristics which
define string insulator units; their values are agreed between purchaser and manufacturer.
Ball and socket couplings are covered by IEC 60120, clevis and tongue couplings by
IEC 60471.
NOTE For the definition of site pollution severity see IEC TS 60815-1.
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 60383-1, Insulators for overhead lines with a nominal voltage above 1000 V – Part 1:
Ceramic or glass insulator units for AC systems – Definitions, test methods and acceptance
criteria
3 Terms and definitions
No terms and definitions are listed in this document.

– 6 – IEC 60305:2021 © IEC 2021
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
4 Mechanical characteristics, dimensions and types
String insulator units of the cap and pin type are standardized by the following specified
characteristics:
– Specified electromechanical or mechanical failing load (SFL) according to IEC 60383-1;
– maximum nominal diameter of the insulating part;
– nominal spacing;
– minimum nominal creepage distance;
– standard coupling.
The corresponding values are indicated in Table 1, Table 2, Table 3, Table 4 and Table 5.
NOTE 1 The following points merit attention for insulators for use in polluted areas:
a) even if the creepage distance is the same, the withstand voltage characteristics may change with shed shape of
the insulators;
b) even if the string length is the same, the withstand voltage characteristics may decrease with increasing
insulator strength due to the lower efficiency of creepage distance for a larger average diameter.
NOTE 2 IEC 60815 gives details on the important parameters of shed profiles for antipollution insulators.
5 Designation and marking with respect to shed profile
Insulators are designated in Table 1, Table 2, Table 3, Table 4 and Table 5 by the letter U
followed by a number indicating the specified electromechanical or mechanical failing load in
kilonewtons.
The letter B or C which follows specifies a ball and socket or clevis and tongue, respectively.
The following letter S or L, if present, specifies a short or long spacing.
The letter P, D, V, or T present for "anti-fog" profile, "aerodynamic" profile, "two-alternating"
profile, or "three-alternating" profile, as shown in Figure 1, Figure 2, Figure 3,Figure 4 and
Figure 5, respectively.
IEC 60383-1 specifies that insulators shall be marked with the specified electromechanical or
mechanical failing load. This load may be indicated by using the first part of the designation
given in the first column of Table 1, Table 2, Table 3, Table 4 and Table 5: For instance, the
insulator may be marked U 160 for the units U 160 BS, U 160 BL and U 160 BLP.

Figure 1 – Typical "standard" profile

Figure 2 – Typical "anti-fog" profile "P"

Figure 3 – Typical "aerodynamic" profile "D"

Figure 4 – Typical "two-alternating" profile "V"

– 8 – IEC 60305:2021 © IEC 2021

Figure 5 – Typical "three-alternating" profile "T"
6 Tolerances
Except for nominal spacing, tolerances for dimensions indicated in IEC 60383-1 are
applicable to all nominal values including maximum nominal diameter and minimum nominal
creepage distance values given in Table 1, Table 2, Table 3, Table 4 and Table 5.
Diagram of Table 1, Table 2, Table 3, Table 4 and Table 5 is shown in Figure 6, Figure 7,
Figure 8, Figure 9 and Figure 10, respectively.
Nominal spacing tolerance shall be:
± (0,03 P + 0,3) mm
P being spacing expressed in millimetres.

Figure 6 – String insulator unit of standard and anti-fog
profile with ball and socket coupling

Table 1 – Specified values of mechanical and dimensional characteristics for string
insulator units of standard and anti-fog profile with ball and socket couplings
Designation Specified Maximum Nominal Minimum Standard
electromechanical nominal spacing nominal coupling
or mechanical diameter of the creepage according to
failing load insulating part distance IEC 60120

kN D P mm d1
mm mm
U 40 B 40 175 110 190 11
U 40 BP 40 210 110 295 11
U 70 BS 70 255 127 295 16
U 70 BL 70 255 146 295 16
U 70 BLP 70 280 146 440 16
U 100 BS 100 255 127 295 16
U 100 BL 100 255 146 295 16
U 100 BLP 100 280 146 440 16
U 120 B 120 255 146 295 16
U 120 BP 120 280 146 440 16
U 160 BS 160 280 146 315 20
U 160 BSP 160 330 146 440 20
U 160 BL 160 280 170 340 20
U 160 BLP 160 330 170 525 20
U 210 B 210 300 170 370 20
U 210 BP 210 330 170 525 20
U 300 B 300 330 195 390 24
U 300 BP 300 400 195 590 24
U 400 B 400 380 205 525 28
U 420 B 420 380 205 525 28
U 530 B 530 380 240 600 32
U 550 B 550 380 240 600 32
U 700 B 700 430 280 600 36
U 840 B 840 430 300 600 40
– 10 – IEC 60305:2021 © IEC 2021

Figure 7 – String insulator unit of standard and anti-fog profile
with clevis and tongue coupling
Table 2 – Specified values of mechanical and dimensional characteristics for string
insulator units of standard and anti-fog profile with clevis and tongue couplings
Designation Specified Maximum Nominal Minimum Standard
electromechanical nominal spacing nominal coupling
or mechanical diameter of the creepage according to
failing load insulating part distance IEC 60471

kN D P mm
mm mm
U 40 C 40 190 140 200 16 C
U 70 C 70 255 146 295 16 C
U 70 CP 70 280 146 440 16 C
U 100 C 100 255 146 295 16 C
U 100 CP 100 280 146 440 16 C
U 120 C 120 255 146 295 16 C
U 120 CP 120 280 146 440 16 C
U 160 C 160 280 170 340 19 C
U 160 CP 160 330 170 525 19 C
U 210 C 210 300 178 370 22 C
U 210 CP 210 330 178 525 22 C
NOTE Insulators having an electromechanical or mechanical failing load exceeding 210 kN are not specified. If
necessary, the insulators with ball and socket coupling defined in Table 1 shall preferably be used.

Figure 8 – String insulator unit of aerodynamic profile with ball and socket coupling
Table 3 – Specified values of mechanical and dimensional characteristics for string
insulator units of aerodynamic profile with ball and socket couplings
Designation Specified Maximum Nominal Minimum Standard
electromechanical nominal spacing nominal coupling
or mechanical diameter of the creepage according to
failing load insulating part distance IEC 60120

kN D P
mm mm mm
U 70 BSD 70 380 127 305 16
U 70 BLD 70 380 146 305 16
U 120 BSD 120 380 127 295 16
U 120 BLD 120 380 146 295 16
U 160 BD 160 425 146 375 20
U 210 BD 210 425 170 375 20
Figure 9 – String insulator unit of two-alternating profile with ball and socket coupling

– 12 – IEC 60305:2021 © IEC 2021
Table 4 – Specified values of mechanical and dimensional characteristics for string
insulator units of two-alternating profile with ball and socket couplings
Designation Specified Maximum Nominal Minimum Standard
electromechanical nominal spacing nominal coupling
or mechanical diameter of the creepage according to
failing load insulating part distance IEC 60120

kN D P
mm mm mm
U 70 BSV 70 280 146 450 16
U 70 BLV 70 280 160 450 16
U 120 BSV 120 280 146 450 16
U 120 BLV 120 280 160 450 16
U 160 BSV 160 290 155 450 20
U 160 BV 160 290 160 450 20
U 160 BLV 160 355 170 450 20
U 210 BV 210 355 170 450 20
U 240 B
...