ISO 10924-1:2025

International
Standard
ISO 10924-1
Third edition
Road vehicles — Circuit breakers —
2025-03
Part 1:
Definitions and general test
requirements
Véhicules routiers — Coupe-circuits —
Partie 1: Définitions et exigences d'essais générales
Reference number
© ISO 2025
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Published in Switzerland
ii
Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Marking, labelling and colour coding . 5
5 Tests and requirements . 5
5.1 General .5
5.1.1 General test conditions .5
5.1.2 General performance requirements .6
5.2 Voltage drop .7
5.2.1 Purpose .7
5.2.2 Test . . .7
5.2.3 Requirement .7
5.3 Maximum housing temperature .7
5.3.1 Purpose .7
5.3.2 Test . . .7
5.3.3 Requirement .7
5.4 Environmental conditions .7
5.4.1 Purpose .7
5.4.2 Mechanical loads .7
5.4.3 Climatic loads .8
5.4.4 Chemical loads .8
5.5 Operating time rating .8
5.5.1 Purpose .8
5.5.2 Test . . .8
5.5.3 Requirement .8
5.6 Current steps .8
5.6.1 Purpose .8
5.6.2 Test . . .9
5.6.3 Requirement .9
5.7 No current trip and reset temperature .9
5.7.1 Purpose .9
5.7.2 Test . . .9
5.7.3 Requirement .9
5.8 Absolute breaking capacity .9
5.8.1 Purpose .9
5.8.2 Test . . .9
5.8.3 Requirement .10
5.9 Breaking capacity .10
5.9.1 Purpose .10
5.9.2 Test . . .10
5.9.3 Requirement .11
5.10 Strength of terminals. 12
5.10.1 Purpose . 12
5.10.2 Test . . . 12
5.10.3 Requirement . 12
5.11 Endurance . 12
5.11.1 Purpose . 12
5.11.2 Test . . . 12
5.11.3 Requirement . 13
5.12 Dielectric strength . 13
5.12.1 Purpose . 13
5.12.2 Test . . . 13
5.12.3 Requirement . 13

iii
Annex A (normative) Cycling profiles . 14
Annex B (normative) Test circuit . 17
Annex C (informative) Temperature rise test . 19

iv
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 32,
Electrical and electronic components and general system aspects.
This third edition cancels and replaces the second edition (ISO 10924-1:2016), which has been technically
revised.
The main changes are as follows:
— in Clause 3 definition of insulation resistance was added;
— in Table 1 more details at the tolerances of measurement values were added;
— in Table 2 the test voltage of the DC power supply u was added;
t
— in 5.8.2 and 5.8.3 the test and requirements for absolute breaking capacity were clarified;
— in 5.9.2 and 5.9.3 the test and requirements for breaking capacity were clarified;
— in 5.11.3 the requirements for endurance were clarified;
— in Annex B Figure B.2 was added;
— Annex C the temperature rise test was added.
A list of all parts in the ISO 10924 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

v
International Standard ISO 10924-1:2025(en)
Road vehicles — Circuit breakers —
Part 1:
Definitions and general test requirements
1 Scope
This document defines terms and specifies general test requirements for circuit breakers for use in road
vehicles with a nominal voltage of 12 V (DC), 24 V (DC), 48 V (DC) and 450 V (DC).
This document is intended to be used in conjunction with ISO 10924-2, ISO 10924-3, ISO 10924-4 and
ISO 10924-5. The numbering of its clauses corresponds to that of the document whose requirements are
applicable, except where modified by requirements particular to this document.
This document is not applicable to circuit breaker holders (electrical centres or fuse-holders) used in
vehicles.
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.
1)
ISO 6722-1 , Road vehicles — 60 V and 600 V single-core cables — Part 1: Dimensions, test methods and
requirements for copper conductor cables
ISO 8820-1, Road vehicles — Fuse-links — Part 1: Definitions and general test requirements
ISO 8820-3, Road vehicles — Fuse-links — Part 3: Fuse-links with tabs (blade type) Type C (medium), Type E
(high current) and Type F (miniature)
ISO 10924-2, Road vehicles — Circuit breakers — Part 2: Guidance for users
ISO 10924-3:2025, Road vehicles — Circuit breakers — Part 3: Miniature circuit breakers with tabs (Blade type),
Form CB11
ISO 10924-4:2025, Road vehicles — Circuit breakers — Part 4: Medium circuit breakers with tabs (Blade type),
Form CB15
ISO 10924-5:2025, Road vehicles — Circuit breakers — Part 5: Circuit breakers with bolt with rated voltage of 450 V
ISO 16750-1, Road vehicles — Environmental conditions and testing for electrical and electronic equipment —
Part 1: General
ISO 16750-3, Road vehicles — Environmental conditions and testing for electrical and electronic equipment —
Part 3: Mechanical loads
ISO 16750-4, Road vehicles — Environmental conditions and testing for electrical and electronic equipment —
Part 4: Climatic loads
ISO 16750-5, Road vehicles — Environmental conditions and testing for electrical and electronic equipment —
Part 5: Chemical loads
1) Withdrawn standard.
IEC 60068-2–70, Environmental testing — Part 2: Tests — Test Xb: Abrasion of markings and letterings caused
by rubbing of fingers and hands
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 16750-1, ISO 8820-1 and the
following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
absolute breaking capacity
value of prospective breaking current that a circuit breaker (3.3) is capable of breaking at least once at U
Smax
under prescribed conditions of use and behaviour
3.2
breaking capacity
I
B
value of prospective breaking current a circuit breaker (3.3) is capable of breaking several times at U
Smax
under prescribed conditions of use and behaviour
3.3
circuit breaker
overcurrent protection device that mechanically interrupts the circuit reversibly, responsive to electric current
Note 1 to entry: The test fixture for the circuit breaker may be identical to the test fixture as described in ISO 8820-3.
However, some circuit breaker designs do not require a separate test fixture as the cables are directly connected to
the circuit breaker terminals (3.4.2).
3.4
Circuit breaker components
3.4.1
housing
electrically non-conductive mechanical support for conductive and non-conductive parts of the circuit
breaker (3.3)
3.4.2
terminal
part of the circuit breaker (3.3) which makes the electrical connection in the electrical circuit
3.4.3
time-delayed element
active part that acts depending on the current and causes the reversible interruption of the circuit in the
case of an overcurrent
3.5
Circuit breaker features
3.5.1
reset mechanism
provides a user interface in a manual reset circuit breaker (3.3) for resetting the device after an overcurrent
condition
3.5.2
snap-action mechanism
ensures that the contact closing speed by mechanical reset is independent of the speed of operation of the
reset mechanism (3.5.1)
3.5.3
switching mechanism
provides the ability to switch off the circuit breaker (3.3) by mechanical means
3.5.4
trip mechanism
comprises a time-delayed actuator and mechanical components
3.5.5
cycling trip free
circuit breaker mechanism that cycles to open and close the contact(s) repeatedly if the actuator is
maintained in the “ON” position in case of overcurrent
3.5.6
fully trip free
circuit breaker mechanism that causes the moving contact(s) to open and remain open, even if the actuator
is maintained in the “ON” position in case of overcurrent
3.5.7
trip free mechanism
prevents the switching mechanism (3.5.3) from being defeated by forcibly holding the actuator “ON” position,
i.e. cannot be held closed against an overload
3.6
Circuit breaker types
3.6.1
type I
automatic reset
device that provides the reversal of an overcurrent condition after a cool-down period without any manual
activity required by a user
3.6.2
type II
electrically reset
device that is opened by overcurrent and remains open as long as a minimum voltage and current is available
to the affected circuit
Note 1 to entry: The type II circuit breaker has a secondary heating circuit which, after an overcurrent condition
occurs, creates heat internally upon the time-delayed element (3.4.3) of the circuit breaker (3.3) to keep it from
reversing as long as the electrical system voltage and a small current flow (<1,0 A) is available, the reset function is
accomplished by removing all electrical power supplied to the circuit breaker until the internal thermal element cools
down and returns to its conductive position.
3.6.3
type III
manual reset
device that contains a reset mechanism (3.5.1) that the user is required to operate manually to reverse a
circuit interruption
3.6.4
type IV
switchable
device that contains a mechanism like type III (3.6.3) and additionally capable of being switched off manually
for user testing or maintenance

3.7
dielectric strength
strength measured between specified measuring points, as shown in ISO 10924-3, ISO 10924-4 and
ISO 10924-5, at a specified voltage without disruptive discharge
3.8
nominal voltage
U
N
voltage value used to describe the electrical system of a vehicle
[SOURCE: ISO 16750-1:2023, 3.13, modified — "12/24 V electrical system" has been replaced by "electrical
system".]
3.9
operating time
time between the application of an overcurrent and the moment when the current drops below a value as
specified in the appropriate part of the ISO 8820 series
[SOURCE: ISO 8820-1:2014, 3.7]
3.10
operating time rating
operating time (3.9), as a function of the current under defined test conditions
[SOURCE: ISO 8820-1:2014, 3.8]
3.11
prospective current
I
P
current, which would flow in a circuit, if the circuit breaker (3.3) would be replaced by a conductor with
negligible impedance
Note 1 to entry: See Figure B.1 for the test circuit.
3.12
rated current
I
R
current used for identifying the circuit breaker (3.3), according to specified tests
Note 1 to entry: The continuous current can be lower than the rated current.
3.13
rated voltage
U
R
maximum supply voltage for which the circuit breaker (3.3) is designed
3.14
rerating factor
correction factor of rated
...