SIST EN 50122-3:2022
(Main)Railway applications - Fixed installations - Electrical safety, earthing and the return circuit - Part 3: Mutual Interaction of AC and DC traction systems
Railway applications - Fixed installations - Electrical safety, earthing and the return circuit - Part 3: Mutual Interaction of AC and DC traction systems
This document specifies requirements for the protective provisions relating to electrical safety in fixed installations, when it is reasonably likely that hazardous voltages or currents will arise for people or equipment, as a result of the mutual interaction of AC and DC electric power supply traction systems.
It also applies to all aspects of fixed installations that are necessary to ensure electrical safety during maintenance work within electric power supply traction systems.
The mutual interaction can be of any of the following kinds:
— parallel running of AC and DC electric traction power supply systems;
— crossing of AC and DC electric traction power supply systems;
— shared use of tracks, buildings or other structures;
— system separation sections between AC and DC electric traction power supply systems.
The scope is limited to galvanic, inductive and capacitive coupling of the fundamental frequency voltages and currents and their superposition.
This document applies to all new lines, extensions and to all major revisions to existing lines for the following electric traction power supply systems:
a) railways;
b) guided mass transport systems such as:
1) tramways,
2) elevated and underground railways,
3) mountain railways,
4) magnetically levitated systems, which use a contact line system,
5) trolleybus systems, and
6) electric traction power supply systems for road vehicles, which use an overhead contact line system;
c) material transportation systems.
The document does not apply to:
a) electric traction power supply systems in underground mines;
b) cranes, transportable platforms and similar transportation equipment on rails, temporary structures (e.g. exhibition structures) in so far as these are not supplied directly or via transformers from the contact line system and are not endangered by the electric traction power supply system for railways;
c) suspended cable cars;
d) funicular railways;
e) procedures or rules for maintenance.
The rules given in this document can also be applied to mutual interaction with non-electrified tracks, if hazardous voltages or currents can arise from AC or DC electric traction power supply systems.
Bahnanwendungen - Ortsfeste Anlagen - Elektrische Sicherheit, Erdung und Rückleitung - Teil 3: Gegenseitige Beeinflussung von Wechselstrom- und Gleichstrombahnen
Applications ferroviaires - Installations fixes - Sécurité électrique, mise à la terre et circuit de retour - Partie 3: Interactions mutuelles entre systèmes de traction en courant alternatif et en courant continu
Le présent document spécifie les exigences relatives aux dispositions de protection concernant la sécurité électrique des installations fixes, lorsqu'il existe un risque raisonnable de présence de tensions ou de cou-rants dangereux pour les personnes ou les équipements, due aux interactions entre systèmes d'alimentation de traction électrique en courant alternatif et continu.
Le présent document s'applique également à tous les aspects des installations fixes, qui sont nécessaires pour assurer la sécurité électrique pendant les travaux de maintenance réalisés au sein des systèmes d'ali-mentation de traction électrique.
Les interactions mutuelles peuvent être de l'un des types suivants :
— le fonctionnement en parallèle de systèmes d'alimentation de traction électrique en courant alternatif et continu ;
— le croisement de systèmes d'alimentation de traction électrique en courant alternatif et continu ;
— l'utilisation partagée des voies, des bâtiments ou d'autres structures ;
— les sections de séparation entre les systèmes d'alimentation de traction électrique en courant alternatif et continu.
Le domaine d'application se limite au couplage galvanique, inductif et capacitif des tensions et courants à la fréquence fondamentale et à leur superposition.
Le présent document s'applique à l'ensemble des lignes nouvelles, ainsi qu'aux extensions et rénovations majeures des lignes existantes pour les systèmes d'alimentation de traction électrique suivants :
a) les réseaux ferroviaires ;
b) les réseaux de transport en commun guidés tels que :
1) les tramways ;
2) les voies ferroviaires aériennes et souterraines ;
3) les voies ferroviaires de montagne ;
4) les systèmes à sustentation magnétique, qui utilisent un système de ligne de contact ;
5) les systèmes de trolleybus ; et
6) les systèmes d'alimentation de traction électrique des véhicules routiers, qui utilisent un système de ligne aérienne de contact ;
c) les systèmes de transport de matériaux.
Le présent document ne s'applique pas aux :
a) systèmes d’alimentation de traction électrique des mines souterraines ;
b) grues, plateformes transportables et autres matériels de transport similaires sur rails, structures tempo-raires (dans les foires et expositions, par exemple) lorsqu'ils ne sont pas alimentés par les lignes aé-riennes de contact, directement ou par des transformateurs, ni affectés par le système d'alimentation électrique de traction ferroviaire ;
c) téléphériques ; télécabines ;
d) téléphériques, télécabines ;
e) procédures ou règles de maintenance.
Les règles établies dans le présent document peuvent également être appliquées à l'interaction mutuelle avec les voies non électrifiées, si des tensions ou courants dangereux peuvent provenir des systèmes d'alimentation de traction électrique en courant alternatif ou continu.
Železniške naprave - Fiksni postroji - Električna varnost, ozemljitev in povratni tokokrog - 3. del: Medsebojno vplivanje med izmeničnimi in enosmernimi sistemi vleke
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-december-2022
Nadomešča:
SIST EN 50122-3:2010
Železniške naprave - Fiksni postroji - Električna varnost, ozemljitev in povratni
tokokrog - 3. del: Medsebojno vplivanje med izmeničnimi in enosmernimi sistemi
vleke
Railway applications - Fixed installations - Electrical safety, earthing and the return circuit
- Part 3: Mutual Interaction of AC and DC traction systems
Bahnanwendungen - Ortsfeste Anlagen - Elektrische Sicherheit, Erdung und Rückleitung
- Teil 3: Gegenseitige Beeinflussung von Wechselstrom- und Gleichstrombahnen
Applications ferroviaires - Installations fixes - Sécurité électrique, mise à la terre et circuit
de retour - Partie 3: Interactions mutuelles entre systèmes de traction en courant
alternatif et en courant continu
Ta slovenski standard je istoveten z: EN 50122-3:2022
ICS:
29.120.50 Varovalke in druga Fuses and other overcurrent
nadtokovna zaščita protection devices
29.280 Električna vlečna oprema Electric traction equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EUROPEAN STANDARD EN 50122-3
NORME EUROPÉENNE
EUROPÄISCHE NORM September 2022
ICS 29.120.50; 29.280 Supersedes EN 50122-3:2010
English Version
Railway applications - Fixed installations - Electrical safety,
earthing and the return circuit - Part 3: Mutual Interaction of AC
and DC traction systems
Applications ferroviaires - Installations fixes - Sécurité Bahnanwendungen - Ortsfeste Anlagen - Elektrische
électrique, mise à la terre et circuit de retour - Partie 3: Sicherheit, Erdung und Rückleitung - Teil 3: Gegenseitige
Interactions mutuelles entre systèmes de traction en Beeinflussung von Wechselstrom- und Gleichstrombahnen
courant alternatif et en courant continu
This European Standard was approved by CENELEC on 2022-07-25. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Türkiye and the United Kingdom.
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2022 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN 50122-3:2022 E
Contents Page
European foreword . 4
1 Scope . 5
2 Normative references . 6
3 Terms and definitions . 6
4 Hazards and adverse effects . 6
4.1 General . 6
4.2 Electrical safety of persons . 6
5 Types of mutual interaction to be considered . 6
5.1 General . 6
5.2 Galvanic coupling . 7
5.2.1 AC and DC return circuits not directly connected . 7
5.2.2 AC and DC return circuits directly connected or common . 7
5.3 Non-galvanic coupling . 7
5.3.1 Inductive coupling . 7
5.3.2 Capacitive coupling . 8
6 Zone of mutual interaction . 8
6.1 General . 8
6.2 Effects of AC railway systems on DC railway systems . 8
6.3 Effects of DC railway systems on AC railway systems . 9
7 Touch voltage limits for the combination of alternating and direct voltages . 9
7.1 General . 9
7.2 Touch voltage limits for long-term conditions . 9
7.3 AC system short-term conditions and DC system long-term conditions . 10
7.4 AC system long-term conditions and DC system short-term conditions . 11
7.5 AC system short-term conditions and DC system short-term conditions . 12
7.6 Workshops and similar locations . 12
8 Technical requirements and measures inside the zone of mutual interaction . 13
8.1 General . 13
8.2 Requirements if the AC railway and the DC railway have separate return circuits . 13
8.2.1 General . 13
8.2.2 Return circuit or parts connected to the return circuit of one system located in the OCLZ
and/or CCZ of the other system . 13
8.2.3 Common buildings and common structures . 14
8.2.4 Inductive and capacitive coupling . 15
8.3 Requirements if the AC railway and the DC railway have common return circuits and use
the same tracks . 15
8.3.1 General . 15
8.3.2 Measures against stray current . 15
8.3.3 Common structures and common buildings . 15
8.3.4 Exceptions . 16
8.3.5 Design of overhead contact line . 16
8.3.6 Inductive and capacitive coupling . 16
8.4 System separation sections and system separation stations . 16
Annex A (informative) Zone of mutual interaction . 17
A.1 General . 17
A.2 AC system as source . 17
A.2.1 Main parameters. 17
A.2.2 Basic analysis . 17
A.2.3 Parameter variations . 20
A.3 DC system as source . 22
Annex B (informative) Analysis of combined voltages . 23
Annex C (informative) Analysis and assessment of mutual interaction . 28
C.1 General . 28
C.2 Analysis of mutual interaction . 28
C.3 System configurations to be taken into consideration . 28
Figures
Figure 1 — Maximum permissible combined effective touch voltages (excluding workshops and
similar locations) for long-term conditions . 10
Figure 2 — Maximum permissible combined effective touch voltages under AC short-term
conditions and DC long-term conditions . 11
Figure 3 — Maximum permissible combined effective touch voltages under AC long-term
conditions and DC short-term conditions . 12
Figure 4 — Maximum permissible combined effective touch voltages in workshops and similar
locations excluding short-term conditions . 13
Figure 5 — Example of where a VLD shall be suitable for both alternating and direct voltage . 14
Figure A.1 — Overview of voltages coupled in as function of distance and soil resistivity I . 18
Figure A.2 — Overview of voltages coupled in as function of distance and soil resistivity II . 19
Figure A.3 — Relation between length of parallelism and zone of mutual interaction caused by an
AC railway . 20
Figure B.1 — Definition of combined peak voltage . 24
Figure B.2 — Overview of permissible combined AC and DC voltages . 25
Figure B.3 — Overview of permissible voltages in case of a duration ≥ 1,0 s both AC voltage and
DC voltage . 26
Figure B.4 — Permissible voltages in case of a duration 0,1 s AC voltage and a duration 300 s DC
voltage . 27
European foreword
This document (EN 50122-3:2022) has been prepared by CLC/SC 9XC “Electric supply and earthing systems
for public transport equipment and ancillary apparatus (Fixed installations)”.
The following dates are fixed:
• latest date by which this document has to be (dop) 2023-07-25
implemented at national level by publication of
an identical national standard or by
endorsement
• latest date by which the national standards (dow) 2025-07-25
conflicting with this document have to be
withdrawn
This document supersedes EN 50122-3:2010 and all of its amendments and corrigenda (if any).
— harmonization with EN 50122-1:2022.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CENELEC shall not be held responsible for identifying any or all such patent rights
This document has been prepared under a Standardization Request given to CENELEC by the European
Commission and the European Free Trade Association.
Any feedback and questions on this document should be directed to the users’ national committee. A complete
listing of these bodies can be found on the CENELEC website.
1 Scope
This document specifies requirements for the protective provisions relating to electrical safety in fixed
installations, when it is reasonably likely that hazardous voltages or currents will arise for people or equipment,
as a result of the mutual interaction of AC and DC electric power supply traction systems.
It also applies to all aspects of fixed installations that are necessary to ensure electrical safety during
maintenance work within electric power supply traction systems.
The mutual interaction can be of any of the following kinds:
— parallel running of AC and DC electric traction power supply systems;
— crossing of AC and DC electric traction power supply systems;
— shared use of tracks, buildings or other structures;
— system separation sections between AC and DC electric traction power supply systems.
The scope is limited to galvanic, inductive and capacitive coupling of the fundamental frequency voltages and
currents and their superposition.
This document applies to all new lines, extensions and to all major revisions to existing lines for the following
electric traction power supply systems:
a) railways;
b) guided mass transport systems such as:
1) tramways,
2) elevated and underground railways,
3) mountain railways,
4) magnetically levitated systems, which use a contact line system,
5) trolleybus systems, and
6) electric traction power supply systems for road vehicles, which use an overhead contact line system;
c) material transportation systems.
The document does not apply to:
a) electric traction power supply systems in underground mines;
b) cranes, transportable platforms and similar transportation equipment on rails, temporary structures (e.g.
exhibition structures) in so far as these are not supplied directly or via transformers from the contact line
system and are not endangered by the electric traction power supply system for railways;
c) suspended cable cars;
d) funicular railways;
e) procedures or rules for maintenance.
The rules given in this document can also be applied to mutual interaction with non-electrified tracks, if
hazardous voltages or currents can arise from AC or DC electric traction power supply systems.
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.
EN 50122-1:2022, Railway applications – Fixed installations – Electrical safety, earthing and the return circuit
– Part 1: Protective provisions against electric shock
EN 50122-2:2022, Railway applications – Fixed installations – Electrical safety, earthing and the return circuit
– Part 2: Provisions against the effects of stray currents caused by DC traction systems
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 50122-1:2022 apply.
ISO and IEC maintain terminological 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/
4 Hazards and adverse effects
4.1 General
The different requirements specified in EN 50122-1:2022 and EN 50122-2:2022, concerning connections to
the return circuit of the AC railway, and connections to the return circuit of the DC railway, shall be taken into
account in order to avoid risks of hazardous voltages and stray currents.
Such hazards and risks shall be considered from the start of the planning of any installation which includes
both AC and DC railways. Suitable measures shall be specified for limiting the voltages to the levels given in
this document, while limiting the damaging effects of stray currents in accordance with EN 50122-2:2022.
Additional adverse effects are possible, for example:
— thermal overload of conductors, screens and sheaths;
— thermal overload of transformers due to magnetic saturation of the cores;
— restriction of operation because of possible effects on the safety and correct functioning of signalling
systems;
— restriction of operation because of malfunction of the communication system.
These effects are not considered in this Standard.
4.2 Electrical safety of persons
Where AC and DC voltages are present together the limits for touch voltage given in Clause 7 apply in addition
to the limits given in EN 50122-1:2022, Clause 9.
5 Types of mutual interaction to be considered
5.1 General
Coupling describes the physical process of transmission of energy from a source to a susceptible device.
The following types of coupling shall be considered:
a) galvanic (conductive) coupling;
b) non-galvanic coupling,
1) inductive coupling,
2) capacitive coupling.
Galvanic coupling dominates at low frequencies, when circuit impedances are low. The effects of galvanic
coupling are conductive voltages and currents.
The effects of inductive coupling are induced voltages and hence currents. These voltages and currents
depend inter alia on the distances, length, inducing current conductor arrangement and frequency.
The effects of capacitive coupling are influenced voltages into galvanically separated parts or conductors. The
influenced voltages depend inter alia on the voltage of the influencing system and the distance. Currents
resulting from capacitive coupling are also depending on the frequency.
NOTE As far as the capacitive and inductive coupling are concerned, general experience is that only the influence of
the AC railway to the DC railway is significant.
5.2 Galvanic coupling
5.2.1 AC and DC return circuits not directly connected
A mutual interaction between the return circuits is possible by currents through earth caused by the rail
potential of both AC and DC railways, for example return currents flowing through the return conductors,
earthing installations of traction substations and cable screens.
In case a conductive parallel path to the return circuit exists in the influenced system, various effects are
possible. In case a vehicle forms part of the parallel path, return current of the influencing railway system can
flow through the propulsion system of the traction unit. The same effects are possible when the return current
of the influencing system flows, for example, through the auto-transformer and substation transformer of an
auto-transformer system or through booster transformers or other devices.
An electric shock with combined voltages can occur when parts of the return circuits or conductive parts which
are connected to the return circuits by voltage limiting devices are located in the overhead contact line zone
of the other railway system, see 8.2.2.
5.2.2 AC and DC return circuits directly connected or common
In addition to the effects described in 5.2.1 current exchange will be increased where AC and DC return circuits
are directly connected or common.
EXAMPLE Direct connections can be railway level crossings, common tracks, system separation sections, etc.
Currents flowing between the AC railway and the DC railway can create mutual interaction between the return
circuits.
Both return circuits are at the same potential at the location of the connection. A short-circuit within the AC
system can cause a peak voltage on conductive structures connected to the return circuit of the DC railway.
The same effects apply for conductive structures connected to it directly or via a voltage limiting device (VLD).
The voltage across the voltage limiting device can trip the device without a fault on the DC side.
The connection of the return circuit of the DC railway to the earthed return circuit of the AC railway increases
the danger of stray current corrosion.
For requirements for fixed installations see 8.3.
5.3 Non-galvanic coupling
5.3.1 Inductive coupling
An AC voltage can be induced on a DC contact line system and on the DC system’s return circuit. This effect
needs to be considered in case the DC railway is within the zone of mutual interaction.
Consequently, an AC voltage can occur within the DC substation at the busbars versus earth (i.e. at the rectifier
or in the feeder cubicles).
Interaction can occur in terms of impermissible touch voltages. See Clause 7.
Perpendicular crossings do not result in inductive effects in the DC system.
5.3.2 Capacitive coupling
Within small distances an AC voltage can be influenced on a DC contact line system when it is isolated with a
disconnector or circuit-breaker open. The possibility shall be considered that the flash-over voltage of the
insulators or of the surge arrestors can be reached.
Distance depends inter alia on geometry and voltage.
An AC voltage can occur within the DC substation at the DC busbars versus earth, i.e. in the feeder cubicles.
Interaction can occur in terms of impermissible touch voltages. See Clause 7.
6 Zone of mutual interaction
6.1 General
The AC railway affects the DC railway and vice-versa by galvanic, inductive and/or capacitive coupling (see
Clause 5). The zone of mutual interaction indicates a distance and a length of parallelism between an AC
railway and a DC railway (see Annex A). The limits of zone of mutual interaction are based on the limits of the
touch voltage given in Clause 7.
If a zone of mutual interaction exists the requirements given in this document shall be fulfilled.
In general no generic values can be given for the zone of mutual interference. An assessment based on local
circumstances has to be made. However when the distance between AC and DC railways is less than 50 m a
zone of mutual interaction is assumed. Distances in excess of 50 m are dealt with in 6.2 and 6.3.
NOTE For information on analysis and assessment of the zone of mutual interaction, see Annex C.
6.2 Effects of AC railway systems on DC railway systems
In case of an AC railway influencing a DC railway the zone of mutual interaction is based on voltages coupled
galvanically and inductively into the affected system. In this Subclause effects of capacitive coupling are
negligible.
For planning purposes the zone of mutual interaction has to be investigated either by calculation or by the
following procedure.
For a system having the characteristics as described below the maximum distance to be considered between
AC and DC railway is 1 000 m:
— double track line, where only the four running rails of the AC railway are used for the return circuit;
— the inducing current is 500 A per overhead contact line (1 000 A in total);
— the length of parallelism between AC and DC railway is 4 km;
— the soil resistivity is 100 Ωm;
— the rated frequency is 50 Hz;
— the affected system is insulated versus earth along its entire length and connected to earth at one end
only;
— screening effects of other parallel metallic objects have not been taken into account.
Where other preconditions apply the dimension of the zone of mutual interaction shall be calculated.
A method for the calculation is given in Annex A.
NOTE The example above is based on a 35 V limit for AC with a time duration longer than 300 s.
In case a DC railway is within the zone of mutual interaction of an AC railway, the level of voltages or currents
coupled into the DC system is not necessarily too high; in this case further analysis of the situation shall be
carried out.
6.3 Effects of DC railway systems on AC railway systems
For the effects of DC railway systems on AC railway systems the dimension of the zone of mutual interaction
can be neglected due to the steep voltage gradient in the soil, caused by the insulated rails.
If the possibility of a galvanic transfer exists, whether temporary or permanent, between conductive parts, then
the zone of mutual interaction is given by the dimensions of those parts. This does not necessarily mean that
the voltages or currents coupled into the AC system are too high, but it does mean that further analysis shall
be carried out to quantify the effects of the coupling
7 Touch voltage limits for the combination of alternating and direct voltages
7.1 General
The limits given in 7.2 to 7.6 are based on touch voltage only and shall not be exceeded. Where an alternating
or a direct voltage is present the touch voltage limits given in EN 50122-1:2022 apply. Other effects with
respect to electrical installations are not taken into account.
The direct and the alternating components of a combined voltage u(t) for time duration in excess of 1 s are
calculated as follows:
𝑡𝑡 +𝑇𝑇
( )
𝑈𝑈 = � 𝑢𝑢𝑡𝑡 d𝑡𝑡 (1)
DC
𝑇𝑇
𝑡𝑡
𝑡𝑡 +𝑇𝑇
𝑈𝑈 = � (𝑢𝑢(𝑡𝑡)−𝑈𝑈 ) d𝑡𝑡 (2)
�
AC DC
𝑇𝑇
𝑡𝑡
where
T = 1 s;
t is the time in seconds (s);
t is the starting time of the time interval (t + T);
0 0
u(t) is the combined voltage;
U is the direct component of combined voltage;
DC
U is the alternating component of combined voltage.
AC
NOTE 1 Formula (1) gives the moving average value of the direct component, and Formula (2) gives the moving RMS
value of the alternating component.
For short-duration phenomena ≤ 1 s the following definitions for alternating voltage and direct voltage are used:
— U is defined as that part of the combined voltage that is caused by the DC system;
DC
— U is defined as that part of the combined voltage that is caused by the AC system.
AC
NOTE 2 Further information on combined voltages is given in Annex B.
NOTE 3 Long-term conditions are associated with operation conditions and short-term conditions are associated with
fault conditions or for example switching operations.
7.2 Touch voltage limits for long-term conditions
The following approach shall be used to check whether the combined voltage is permissible:
1) the alternating part of the combined voltage shall not exceed the maximum permissible alternating body
voltage as given in EN 50122-1:2022, Table 7 for the applicable duration;
2) the direct part of the combined voltage shall not exceed the maximum permissible direct body voltage as
given in EN 50122-1:2022, Table 9 for the applicable duration;
3) the combined voltage is permissible if it is within the envelope as given for the applicable duration in
Figure 1;
4) for time durations in excess of 1 s the combined peak value (see explanation in Annex B) shall be less
than 2 × √2 times the maximum permissible alternating body voltage as given in EN 50122-1:2022,
Table 7 for the applicable duration irrespective of frequency content.
EXAMPLE Assuming the maximum permissible direct touch voltage of 120 V being present in the DC system the
alternating voltage limit is 35 V, see Figure 1. Assuming the maximum permissible alternating touch voltage of 60 V being
present in the AC system the direct voltage limit is 85 V, see Figure 1.
Figure 1 — Maximum permissible combined effective touch voltages
(excluding workshops and similar locations) for long-term conditions
7.3 AC system short-te
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