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INTERNATIONAL TELECOMMUNICATION UNION
STUDY GROUP 5
TELECOMMUNICATION
STANDARDIZATION SECTOR
ID-2005R1
English only
STUDY PERIOD 2013-2016
Original: English
Questions
2/5, 4/5
Geneva, 15-19 June 2015
INPUT DOCUMENT
Source:
Bourns Ltd
Title:
Voltage environment classifications of IEC safety standards
This document considers the voltage environments described in the IEC 60950-1 and IEC 62368-1
safety standards. The hazard-based IEC 62368-1 safety standard approach is the long term
replacement of the established IEC 60950-1 safety standard. Unfortunately the voltage environment
descriptive terms used in each standard are different. This document attempts to describe the
commonalities and differences of the IEC 60950-1 and IEC 62368-1 terms and definitions in the
format of a Recommendation Appendix.
Appendix I
Voltage environment classifications of IEC safety standards
(This appendix does not form an integral part of this Recommendation.)
I.1 Introduction
This Appendix describes the commonalities and differences of the IEC 60950-1 and IEC 62368-1
terms and definitions used to describe various voltage environments. The hazard-based IEC 623681 safety standard approach is the long term replacement of the established IEC 60950 safety
standard. Many ITU-T recommendations reference the IEC 60950-1 voltage environments and this
Appendix provides the linkage between the two IEC standards and might be used in an ITU-T
Recommendation K.50 revision.
I.2 IEC 60950-1:2005: Information technology equipment - Safety - Part 1: General
requirements
The voltage environment conditions are given in general terms in the following definitions.
primary circuit [b-IEC 60950-1]: circuit that is directly connected to the AC mains supply
NOTE It includes, for example, the means for connection to the AC mains supply, the primary windings of
transformers, motors and other loading devices. Conductive parts of an interconnecting cable may be part of a primary
circuit as stated in 1.2.11.6.
secondary circuit [b-IEC 60950-1]: circuit that has no direct connection to a primary circuit and
derives its power from a transformer, converter or equivalent isolation device, or from a battery
NOTE Conductive parts of an interconnecting cable may be part of a secondary circuit as stated in 1.2.11.6.
Contact:
Michael J Maytum
Bourns Ltd
UK
Tel: 01234838589
Email: [email protected]
Attention: This is not a publication made available to the public, but an internal ITU-T Document intended only for use by the
Member States of ITU, by ITU-T Sector Members and Associates, and their respective staff and collaborators in their ITU related
work. It shall not be made available to, and used by, any other persons or entities without the prior written consent of ITU-T.
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SELV circuit [b-IEC 60950-1]: secondary circuit that is so designed and protected that under
normal operating conditions and single fault conditions, its voltages do not exceed a safe value
TNV circuit [b-IEC 60950-1]: circuit that is in the equipment and to which the accessible area of
contact is limited and that is so designed and protected that, under normal operating conditions and
single fault conditions (see 1.4.14), the voltages do not exceed specified limit values
A TNV circuit is considered to be a secondary circuit in the meaning of this (sic IEC 60950-1)
standard.
TNV-1 circuit [b-IEC 60950-1]: TNV circuit whose normal operating voltages do not exceed the
limits for an SELV circuit under normal operating conditions and on which overvoltages from
telecommunication networks and cable distribution systems are possible
TNV-2 circuit [b-IEC 60950-1]: TNV circuit whose normal operating voltages exceed the limits
for an SELV circuit under normal operating conditions and which is not subject to overvoltages
from telecommunication networks
TNV-3 circuit [b-IEC 60950-1]: TNV circuit whose normal operating voltages exceed the limits
for an SELV circuit under normal operating conditions and on which overvoltages from
telecommunication networks and cable distribution systems are possible
In the body of the standard the following voltage limits are defined:
In an SELV circuit the voltages between any two conductors of the SELV circuit or circuits and
between any one such conductor and earth shall not exceed 42.4 V rms maximum, or 60 V d.c..
Under a single fault condition and for periods of less than 200 ms the voltage shall not exceed 71 V
rms maximum or 120 V d.c..
In a telecommunication network the transient overvoltage is assumed to be 1.5 kV peak in TNV-1
circuit and a TNV-3 circuit. IEC 60950 in clause G.3 specifies an 800 V peak transient overvoltage
for an SELV circuit and a TNV-2 circuit if they are connected to a telecommunication network, yet
the SELV and TNV-2 definitions say they are not subject to overvoltages.
From the conditions and values provided Table I.1 can be made to summarize the environments.
Table I.1 IEC 60950-1 voltage environments
Condition
Voltage environment
SELV
TNV-1
TNV-2
d.c. supply voltage and signal (V)
< 60
< 60
Single fault supply voltage < 0.2 s (V)
< 120
< 1500 for < 1 ms
< 400 after 14 ms
see NOTE 1
< 1500 for < 1 ms
< 400 after 14 ms
see NOTE 1
< 1500 for < 1 ms
< 400 after 14 ms
see NOTE 1
Telecommunications overvoltage (V)
NA
see NOTE 2
1500, 10/700 impulse
NA
see NOTE 2
1500, 10/700 impulse
> 60
TNV-3
> 60
NOTE 1: See IEC 60950-1 Figure 2F for other voltage-time values.
NOTE 2: IEC 60950-1 clause G.3 states an 800 V peak transient overvoltage for an SELV circuit and a TNV-2 circuit if they are connected to a
telecommunication network.
I.3 IEC 62368-1:2014: Audio/video, information and communication technology equipment Part 1: Safety requirements
In IEC 62368-1, the voltage environment conditions are not defined in the terms clause but are
given in the body text. Electrical environment classification is by means of the available electrical
Energy Source, ES, and there are three ES classes; ES1, ES2 and ES3. Being energy sources the
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classifications cover far more than just voltage. Annex W (informative) does supply a comparison
of IEC 60950-1 and IEC 62368-1 terms. Definitions of the ES classes can be extracted from Annex
W.
electrical energy source (ES) class[b-IEC 62368-1]: prospective touch voltage and the touch
current under normal operating conditions, abnormal operating conditions, and single fault
conditions determined the class of energy source.
normal operating condition [b-IEC 62368-1]: mode of operation that represents as closely as
possible the range of normal use that can reasonably be expected
Note 1 to entry: Unless otherwise stated, the most severe conditions of normal use are the most unfavourable default
values as specified in Clause B.2.
Note 2 to entry: Misuse is not covered by normal operating conditions. Instead, it is covered by abnormal operating
conditions
abnormal operating condition [b-IEC 62368-1]: temporary operating condition that is not a
normal operating condition and is not a single fault condition of the equipment itself
Note 1 to entry: Abnormal operating conditions are specified in Clause B.3.
Note 2 to entry: An abnormal operating condition may be introduced by the equipment or by a person.
Note 3 to entry: An abnormal operating condition may result in a failure of a component, a device or a safeguard.
single fault condition [b-IEC 62368-1]: condition of equipment with a fault under normal
operating condition of a single safeguard (but not a reinforced safeguard) or of a single component
or a device
Note 1 to entry: Single fault conditions are specified in Clause B.4.
electrical energy source class 1, ES1 [b-IEC 62368-1]: class 1 electrical energy source with levels
not exceeding ES1 limits under normal operating conditions and abnormal operating conditions
that do not lead to a single fault conditions and not exceeding ES2 limits under single fault
conditions of a basic safeguard.
NOTE ES1 may be accessible to an ordinary person (user in IEC 60950-1 terms). ES1 effects are; not painful on the
body, but may be detectable and ignition of combustible materials not likely
electrical energy source class 2, ES2 [b-IEC 62368-1]: class 2 electrical energy source with levels
not exceeding ES2 limits under normal operating conditions, abnormal operating conditions, and
single fault conditions, but is not ES1.
NOTE ES2 may be accessible to an instructed person (no IEC 60950-1 equivalent to someone under supervision). ES2
effects are; painful on the body, but not an injury Ignition of combustible materials possible, but limited growth and
spread of fire
electrical energy source class 3, ES3 [b-IEC 62368-1]: class 3 electrical energy source with one
or more parameters exceeding ES2 limits
NOTE ES3 may be accessible to a skilled person (service person in IEC 60950-1 terms). ES3 effects are; injury to the
body and ignition of combustible materials likely with rapid growth and spread of fire
ordinary person [b-IEC 62368-1]: person who is neither a skilled person nor an instructed person
instructed person [b-IEC 62368-1]: person instructed or supervised by a skilled person as to
energy sources and who can responsibly use equipment safeguards and precautionary safeguards
with respect to those energy sources
Note 1 to entry: Supervised, as used in the definition, means having the direction and oversight of the performance of
others.
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skilled person [b-IEC 62368-1]: person with relevant education or experience to enable him or her
to identify hazards and to take appropriate actions to reduce the risks of injury to themselves and
others
basic safeguard [b-IEC 62368-1]: safeguard that provides protection under normal operating
conditions and under abnormal operating conditions whenever an energy source capable of causing
pain or injury is present in the equipment
prospective touch voltage [b-IEC 62368-1]: voltage between simultaneously accessible
conductive parts when those conductive parts are not being touched
touch current [b-IEC 62368-1]: electric current through a human body when body parts touch two
or more accessible parts or one accessible part and earth
Compared to a voltage source an energy source has additional attributes and some parameters may
have a range of values e.g. capacitance value with voltage in a given class. To fully understand the
energy source class requirements clause 5, Electrically-caused injury, must be read.
From the clause 5 conditions and values Table I.2 summarizes spot parameter values for
comparison with Table I.1. For ES1 and ES2 energy sources all the parameters must conform to the
class requirements. An ES3 energy source has one or more parameters that exceed ES2 limit values.
Table I.2 IEC 62368-1 energy source parameters
Condition
Energy source parameters
ES1
ES2
ES3
Steady state (> 2 s) d.c. supply touch voltage (V)
see NOTE 1
< 60
< 120
> 120
Single fault supply touch voltage 0.2 s to 2 s (V)
< 60
see NOTE 5
< 120
> 120
Single fault supply touch voltage for < 0.2 s (V)
< 60
see NOTE 5
< 198 for < 10 ms
< 150 for < 50 ms
see NOTE 2
> 198 for < 10 ms
> 150 for < 50 ms
see NOTE 2
DC touch current (mA)
<2
< 25
> 25
Single fault supply touch current 0.2 s (mA)
<2
see NOTE 6
<62
> 62
Single fault supply touch current for < 0.2 s (mA)
<2
see NOTE 6
< 200 for < 10 ms
< 107 for < 50 ms
see NOTE 7
> 200 for < 10 ms
> 107 for < 50 ms
see NOTE 7
Capacitance of charged capacitor (nF)
See NOTE 3
300 or greater
300 or greater
> 300 or greater
External paired conductor circuit overvoltage (V)
See NOTE 4
1500,
10/700 impulse
1500,
10/700 impulse
> 1500,
10/700 impulse
NOTE 1 Applies to normal operating conditions, abnormal operating conditions, and single fault conditions for periods greater than 2 s.
NOTE 2 Other time values of voltage are given in IEC 62368-1 Table 6
NOTE 3 Value given is for the steady state supply voltage.
Other capacitance values for different voltages are given in IEC 62368-1 Table 5
NOTE 4 Only differential if one conductor is earthed in the equipment.
NOTE 5 ES1 values from IEC 62368 Table 6 quoted. However, under single fault conditions of a basic safeguard the single fault ES2 limits apply.
NOTE 6 ES1 values from IEC 62368 Table 7 quoted. However, under single fault conditions of a basic safeguard the single fault ES2 limits apply.
NOTE 7 Other time values of current are given in IEC 62368-1 Table 7
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I.4 Summary
From a safety perspective the following approximations can be made according to IEC 62368-1.
Table I.3 Power source safety equivalence of IEC 60950-1 and IEC 62368-1
IEC 60950-1
IEC 62368-1
SELV
ES1
TNV-1
ES1
External circuits have impulse testing see NOTES 1 through 3
TNV-2
ES2
TNV-3
ES2
External circuits have impulse testing see NOTES 1 through 3
NOTE 1 Paired conductor (shielded or unshielded) - tested with1500 V, 10/700.
Only differential if one conductor is earthed in the equipment
NOTE 2 Any other conductors – tested with mains transient or known external circuit overvoltage impulse
whichever is higher. The external circuit is not earthed at either end, but there is an earth reference
NOTE 3 Cable distribution network coaxial cable – tested with 4000 V, 10/700 centre conductor to shield cable
(shield is earthed at the equipment).
Not applicable to power-fed coaxial repeaters.
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