SIST-TP CLC/TR 50480:2011
Determination of cross-sectional area of conductors and selection of protective devices
Determination of cross-sectional area of conductors and selection of protective devices
This Technical Report applies to low-voltage installations with a nominal system frequency of 50 Hz in which the circuits consist of insulated conductors, cables or busbar trunking systems.
It defines the different parameters used for the calculation of the characteristics of electrical wiring
systems in order to comply with rules of HD 384/HD 60364.
These rules are mainly the following:
- current-carrying capacities of the conductors;
- characteristics of protective devices in regard to protection against overcurrent;
- verification of thermal stress in conductors due to short-circuit current or earth fault current;
- fault protection (protection against indirect contact) in TN systems and IT systems;
- limitation of voltage drop;
- verification of mechanical stresses during short-circuit in busbar trunking systems (BTS) according to EN 60439-2 or powertrack systems according to EN 61534 series.
The calculations provided in this Technical Report are only applicable where the characteristics of the circuits are known.
For the purpose of this document, when referring to Busbar Trunking Systems, Powertrack Systems
are also considered.
NOTE 1 Mechanical stress during short-circuit is covered by IEC 60865.
NOTE 2 In general these calculations concern supply by HV/LV transformer, but they are also applicable to supply by LV/LV transformer and LV back-up generators.
NOTE 3 Effects of harmonics currents are not covered by this document.
This Technical Report is also applicable for checking the compliance of the results of calculations
performed by software programs for calculation of cross-sectional area of insulated conductors, crosssectional area of cables and characteristics for selection of busbar trunking systems with
HD 384/HD 60364.
Festlegung von Leiterquerschnitten und Auswahl von Schutzeinrichtungen
Détermination des sections des conducteurs et choix des dispositifs de protection
Določanje prereza vodnikov in izbira zaščitnih naprav
To tehnično poročilo velja za nizkonapetostne inštalacije z nazivno frekvenco sistema 50 Hz, pri katerih so vezja sestavljena iz izoliranih prevodnikov, kablov ali zbiralčnih razdelilnih sistemov.
Opredeljuje različne parametre, ki se uporabljajo za izračun značilnosti električnih inštalacijskih sistemov, da ustrezajo pravilom HD 384/HD 60364.
Pravila so v glavnem naslednja:
- zmožnosti prevodnikov za prenos toka;
- značilnosti zaščitnih naprav v zvezi z zaščito pred nadtokom;
- preverjanje termične napetosti v prevodnikih zaradi kratkega stika ali toka zaradi napake pri ozemljitvi;
- zaščita pred okvaro (zaščita pred posrednim stikom) v sistemih TN in sistemih IT;
- omejitev padca napetosti;
- preverjanje mehanske napetosti med kratkim stikom v zbiralčnih razdelilnih sistemih (BTS) v skladu z EN 60439-2 ali tračnih napajalnih sistemih v skladu s serijo EN 61534.
Izračuni, ki jih zagotavlja to tehnično poročilo, veljajo le tam, kjer so znane značilnosti vezja.
Za namen tega dokumenta zbiralčni razdelilni sistemi pomenijo tudi tračne napajalne sisteme.
OPOMBA 1 Mehansko napetost med kratkim stikom zajema IEC 60865.
OPOMBA 2: Na splošno ti izračuni veljajo za napajanje prek transformatorjev VN/NN, veljajo pa tudi za napajanje prek transformatorjev NN/VN in rezervnih generatorjev NN.
OPOMBA 3: Ta dokument ne zajema učinkov harmonskih tokov.
To tehnično poročilo velja tudi za preverjanje skladnosti rezultatov izračunov, ki so jih izvedli računalniški programi za izračun prereza izoliranih prevodnikov, prereza kablov in značilnosti za izbiro zbiralčnih razdelilnih sistemov, s HD 384/HD 60364.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST-TP CLC/TR 50480:2011
01-maj-2011
1DGRPHãþD
SIST R064-003:2000
'RORþDQMHSUHUH]DYRGQLNRYLQL]ELUD]DãþLWQLKQDSUDY
Determination of cross-sectional area of conductors and selection of protective devices
Festlegung von Leiterquerschnitten und Auswahl von Schutzeinrichtungen
Détermination des sections des conducteurs et choix des dispositifs de protection
Ta slovenski standard je istoveten z: CLC/TR 50480:2011
ICS:
29.060.01 (OHNWULþQHåLFHLQNDEOLQD Electrical wires and cables in
VSORãQR general
91.140.50 Sistemi za oskrbo z elektriko Electricity supply systems
SIST-TP CLC/TR 50480:2011 en,fr
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST-TP CLC/TR 50480:2011
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SIST-TP CLC/TR 50480:2011
TECHNICAL REPORT
CLC/TR 50480
RAPPORT TECHNIQUE
February 2011
TECHNISCHER BERICHT
ICS 29.050 Supersedes R064-003:1998
English version
Determination of cross-sectional area of conductors and selection of
protective devices
Détermination des sections des Festlegung von Leiterquerschnitten und
conducteurs et choix des dispositifs de Auswahl von Schutzeinrichtungen
protection
This Technical Report was approved by CENELEC on 2011-01-02.
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, Romania, Slovakia, Slovenia,
Spain, Sweden, Switzerland and the United Kingdom.
CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
Management Centre: Avenue Marnix 17, B - 1000 Brussels
© 2011 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. CLC/TR 50480:2011 E
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CLC/TR 50480:2011 - 2 -
Foreword
This Technical Report was prepared by CENELEC Technical Committee 64, Electrical installations and
protection against electric shock.
The text of the draft was circulated for voting in accordance with the Internal Regulations, Part 2,
Subclause 11.4.3.3 (simple majority) and was approved by CENELEC as CLC/TR 50480 on
2011-01-13.
This Technical Report supersedes R064-003:1998.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN and CENELEC shall not be held responsible for identifying any or all such patent
rights.
__________
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Contents
Foreword . - 2 -
Introduction . - 5 -
1 Scope . - 6 -
2 Reference documents . - 7 -
3 Symbols . - 8 -
4 Parameters . - 13 -
4.1 General . - 13 -
4.2 Conductor resistances . - 15 -
4.3 Conductor reactances. - 15 -
5 Characteristics of installations . - 16 -
6 Characteristics of the supply source . - 19 -
6.1 Voltage . - 19 -
6.2 Supply by HV/LV transformers . - 19 -
6.3 Supply by generators . - 20 -
6.4 Contribution of asynchronous motors . - 20 -
6.5 LV supply . - 21 -
6.6 Capacitors . - 21 -
7 Characteristics of protective devices. - 21 -
7.1 Circuit-breakers . - 21 -
7.2 Fuses . - 22 -
8 Protection against overload currents. - 22 -
8.1 Current-carrying capacity . - 22 -
8.2 Coordination between conductors and overload protective devices . - 22 -
9 Determination of breaking capacity of protective devices . - 24 -
9.1 General . - 24 -
9.2 Three line maximum short-circuit current . - 24 -
9.3 Line-to-line maximum short-circuit current . - 25 -
9.4 Line-to-neutral maximum short-circuit current . - 26 -
10 Ability to withstand electro-dynamic stresses for busbar trunking systems . - 27 -
11 Fault protection (protection against indirect contact). - 28 -
11.1 Disconnecting time . - 28 -
11.2 Calculation of earth fault current I . - 28 -
ef
12 Verification of thermal stress in conductors . - 29 -
12.1 Thermal stress . - 29 -
12.2 Minimum short-circuit current . - 30 -
12.3 Calculation of the minimum short-circuit current . - 31 -
13 Voltage drop . - 32 -
Annex A Conductor resistances . - 34 -
Bibliography . - 34 -
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Figures
Figure 1 – Examples of installation configurations and impedances used in this document . - 13 -
Figure 2 – Examples of installation configurations and impedances used in this clause . - 25 -
Tables
Table 1 − Resistivity at 20 °C in accordance with IEC 60909, in mΩ⋅mm² / m . - 13 -
Table 2 − Resistivity at various temperatures . - 14 -
Table 3 − Reactance per metre of conductors of cables ( x ) . - 14 -
Table 4 − Selection of resistivity and reactance for insulated conductors and cables. - 16 -
Table 5 − Selection of resistance and reactance for busbar trunking systems . - 17 -
Table 6 − Elements to take into account when calculating maximum and minimum short circuit currents
and earth fault currents. - 18 -
Table 7 − Voltage factor c . - 19 -
Table 8 − Values of k . - 21 -
M
Table 9 − Peak factor (n) . - 27 -
Table 10 − Maximum disconnecting time for TN and TT systems and for IT systems in case of a
second fault . - 28 -
Table 11 − Values of the factor k . - 30 -
Table A.1 − Conductor AC resistances at 20 °C, mΩ / m . - 34 -
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Introduction
The harmonised rules for the erection of electrical low voltage installations, HD 384/HD 60364, require
selection, dimensioning and calculation for the components of an electrical installation.
In complex installations long and detailed calculations may be needed. The rules of HD 384/HD 60364
give the basic principles without the details necessary for an accurate application.
Computers with appropriate software enable the applicable rules for the determination of conductor
cross-section area and selection of protective devices to be applied readily.
It is important that the results of such software programs are in accordance with the harmonised rules.
Therefore this Technical Report defines the different reference parameters necessary for the
calculation of the cross-sectional area of the conductors and for the selection of the protective devices.
It also gives the reference methods for calculation according to the different safety rules defined in the
Harmonisation Documents of the series HD 384/HD 60364.
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1 Scope
This Technical Report applies to low-voltage installations with a nominal system frequency of 50 Hz in
which the circuits consist of insulated conductors, cables or busbar trunking systems.
It defines the different parameters used for the calculation of the characteristics of electrical wiring
systems in order to comply with rules of HD 384/HD 60364.
These rules are mainly the following:
- current-carrying capacities of the conductors;
- characteristics of protective devices in regard to protection against overcurrent;
- verification of thermal stress in conductors due to short-circuit current or earth fault current;
- fault protection (protection against indirect contact) in TN systems and IT systems;
- limitation of voltage drop;
- verification of mechanical stresses during short-circuit in busbar trunking systems (BTS)
according to EN 60439-2 or powertrack systems according to EN 61534 series.
The calculations provided in this Technical Report are only applicable where the characteristics of the
circuits are known.
For the purpose of this document, when referring to Busbar Trunking Systems, Powertrack Systems
are also considered.
NOTE 1 Mechanical stress during short-circuit is covered by IEC 60865.
NOTE 2 In general these calculations concern supply by HV/LV transformer, but they are also applicable to supply
by LV/LV transformer and LV back-up generators.
NOTE 3 Effects of harmonics currents are not covered by this document.
This Technical Report is also applicable for checking the compliance of the results of calculations
performed by software programs for calculation of cross-sectional area of insulated conductors, cross-
sectional area of cables and characteristics for selection of busbar trunking systems with
HD 384/HD 60364.
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2 Reference documents
The following referenced documents are indispensable for the application 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 60076 series Power transformers (IEC 60076 series)
EN 60228 Conductors of insulated cables (IEC 60228)
EN 60269 series Low voltage fuses (IEC 60269 series)
EN 60269-1 Low-voltage fuses - Part 1: General requirements (IEC 60269-1)
HD 60269-2 Low-voltage fuses - Part 2: Supplementary requirements for fuses for use
by authorized persons (fuses mainly for industrial application) - Examples
of standardized systems of fuses A to J (IEC 60269-2)
HD 60269-3 Low-voltage fuses - Part 3: Supplementary requirements for fuses for use
by unskilled persons (fuses mainly for household or similar applications) -
Examples of standardized systems of fuses A to F (IEC 60269-3)
EN 60439-1 1999 Low-voltage switchgear and controlgear assemblies - Part 1: Type-tested
and partially type-tested assemblies (IEC 60439-1:1999)
EN 60439-2 2000 Low-voltage switchgear and controlgear assemblies - Part 2: Particular
requirements for busbar trunking systems (busways) (IEC 60439-2:2000)
EN 60898 series Electrical accessories - Circuit-breakers for overcurrent protection for
household and similar installations (IEC 60898 series)
EN 60947-2 Low-voltage switchgear and controlgear - Part 2: Circuit-breakers
(IEC 60947-2)
EN 61439-1 2009 Low-voltage switchgear and controlgear assemblies - Part 1: General rules
(IEC 61439-1:2009, mod.)
EN 61534 series Powertrack systems (IEC 61534 series)
HD 384/HD 60364 series Low-voltage electrical installations (IEC 60364 series)
HD 60364-4-41 2007 Low-voltage electrical installations - Part 4-41: Protection for safety -
Protection against electric shock (IEC 60364-4-41:2005, mod.)
HD 60364-4-43 2010 Low-voltage electrical installations - Part 4-43: Protection for safety -
Protection against overcurrent (IEC 60364-4-43:2008, mod. + corrigendum
October 2008)
HD 60364-5-52, 2010 Low-voltage electrical installations - Part 5-52: Selection and erection of
electrical equipment - Wiring systems (IEC 60364-5-52:2009, mod. )
HD 384-5-54 Electrical installation of buildings - Part 5: Selection and erection of
electrical equipment - Chapter 54: Earthing arrangements and protective
conductors (IEC 60364-5-54)
IEC 60909 series Short-circuit currents in three-phase a.c. systems (IEC 60909 series)
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3 Symbols
In this Technical Report, the following symbols are used:
I Current ensuring effective operation in conventional time of the protective device and
2
generally given in the product standard, [A]
I Design current of the circuit being considered, [A] (IEV 826-11-10)
B
I Earth fault current, [kA]
ef
I Nominal current of the protective device (fuse rating or breaker setting), [A]
n
I Rated current of busbar trunking system, at an ambient temperature of 30 °C, [A]
nc
I Maximum peak value of highest short-circuit current, [kA]
p
''
I Initial symmetrical short-circuit current at the feeder connection point Q [kA]
kQ
I Steady state short-circuit current for a line-to-neutral short circuit [kA]
k1
I Steady state short-circuit current for a line-to-line short circuit [kA]
k2
I Steady state short-circuit current for a three line short circuit [kA]
k3
NOTE 1 In some cases the I can be higher than the I (e.g. at the terminals of the delta-star transformer).
k1 k3
I Continuous current-carrying capacity of cable, insulated conductors or busbar
Z
trunking system as applied in a circuit [A]
2
( I ⋅ t ) Thermal stress capacity of line, neutral or PE (PEN) conductor given in general for one
0 0
second, [A².s], (IEV 447-07-17)
2
( I ⋅ t ) Thermal stress capacity of line, neutral or PE (PEN) conductor given in general for one
cw cw
second for busbar trunking systems, [A².s], (EN 60439-2, 4.3)
l Route length (insulated conductors and cables), [m], subscript u: upstream
1
subscript d: downstream
l Length of BTS (Busbar Trunking System), [m] subscript u: upstream
2
subscript d: downstream
R Resistance of the conductor between the transformer and the main switchboard [mΩ]
C
R Resistance of line conductor per metre, consisting of insulated conductor or cable, at
c1 ph
steady-state operating temperature, [mΩ/m]
R Resistance of neutral conductor per metre, consisting of insulated conductor or cable, at
c1 N
steady-state operating temperature, [mΩ/m]
R Resistance of protective earthing conductor per metre, consisting of insulated conductor
c1 PE
or cable, at steady-state operating temperature, [mΩ/m]
R Resistance of the neutral conductor upstream of the circuit being considered,
N
R = R , [mΩ]
N ∑ neutral
R Resistance of the protective conductor from the main equipotential bonding to the origin of
PE
the circuit being considered,
R = R , [mΩ]
PE ∑ protective conductor
R Resistance of the PEN conductor from the main equipotential bonding to the origin of the
PEN
circuit being considered,
R = R , [mΩ]
PEN PEN conductor
∑
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R Resistance of the HV network, [mΩ]
Q
R Resistance of the LV upstream network, [mΩ]
SUP
R Resistance of the transformer, [mΩ]
T
R Mean ohmic resistance of BTS (BusbarTrunking System) per meter, per line, at 20 °C,
b0 ph
[mΩ / m]
R Mean ohmic resistance of BTS per meter, per line, at rated current I , at the steady-state
b1 ph nc
operating temperature, [mΩ / m]
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Symbols used for resistances in the context of short-circuits in busbar trunking systems
1
2
3
N
R Three-line short-circuit
bxph
PE
1
2
3
R Line to line short-circuit
bxph ph
N
between L1 and L2, note may
PE
be between any two lines
1
2
3
N
R Line to neutral short-circuit
bxph-N
PE
between L1 and N
1
2
3
N
R fault between L1 and PE
bxph-PE
PE
NOTE 2 The val ue of x depends on the circuit configuration and on the type of protective device, see Table 5.
NOTE 3 For busbar trunking systems the subscript ph is used in order to align with the symbols used in
EN 60439-2.
R Resistive term of mean line-line, line-neutral or line-PE (-PEN) BTS loop impedance per
b0
Ω / m]
metre, at 20 °C, [m
R Resistive term of mean line-line, line-neutral or line-PE (-PEN) BTS loop impedance per
b1
metre, at rated current I , at the steady-state operating temperature, [mΩ / m]
nc
R Resistive term of mean line-line, line-neutral or line-PE (-PEN) BTS loop impedance per
b2
metre, at the mean temperature between the operating temperature at rated current Inc, and
the maximum temperature under short-circuit conditions, [mΩ / m]
R Resistance from the LV side of the upstream network (LV + MV) upstream the main
SUP
switchboard, [mΩ]
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R Resistance of line conductors upstream of the circuit being considered up to the main
U
switchboard
R = R , [mΩ]
u ∑ line
S Cross-sectional area of conductors, [mm²]
S Cross-sectional area of neutral conductor, [mm²]
N
S Cross-sectional area of protective conductor, [mm²]
PE
S Cross-sectional area of PEN conductor, [mm²]
PEN
S Short-circuit power of the high-voltage network, [kVA]
kQ
''
S Initial symmetrical short-circuit power of the high-voltage network, [kVA]
kQ
S Rated apparent power of a generator [kVA]
rG
S Rated apparent power of the motor, [kVA]
rM
S Rated apparent power of the transformer [kVA]
rT
S Cross-sectional area of line conductor, [mm²]
ph
t Rated transformation ratio at which the on-load tap-changer is in the main position
r
U Line to neutral nominal voltage of the installation, [V]
o
U Line to line nominal voltage of the installation, [V]
n
U Nominal system voltage at the feeder connection point Q (HV side), [V]
nQ
U Rated voltage of the transformer on the low voltage side, [V]
rT
X Reactance of the conductor between the transformer and the main switch board [mΩ]
C
X Reactance of line conductor per metre, consisting of insulated conductor or cable, [mΩ/m]
C ph
X' Transient reactance on direct axis [mΩ]
d
x' Transient reactance on direct axis [%]
d
X Reactance of the neutral conductor upstream of the circuit being considered,
N
X = X , [mΩ]
N neutral
∑
X Zero-sequence reactance [mΩ]
0
x Zero-sequence reactance [%]
0
X Reactance of the protective conductor from the main equipotential bonding to the origin of
PE
the circuit being considered,
X = X ,[mΩ]
PE protective conductor
∑
X Reactance of the PEN conductor from the main equipotential bonding to the origin of the
PEN
circuit being considered,
X = X , [mΩ]
PEN PEN conductor
∑
X Reactance of the HV network, [mΩ]
Q
X Reactance from the LV side of the upstream network (LV + MV) upstream the main
SUP
switchboard, [mΩ]
X Reactance of the transformer, [mΩ]
T
X Reactance term of mean line-line, line-neutral or line-PE (-PEN) BTS loop impedance per
b
metre, [mΩ / m]
X Mean reactance of BTS line conductor, per meter, [mΩ / m]
b ph
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X Reactance of line conductors upstream of the circuit being considered up to the main
U
switchboard,
X = X , [mΩ]
U ∑ line
Z Impedance of the conductor between the transformer or the generator and the main
C
switch board [mΩ]
Z Impedance of the generator [mΩ]
G
Z Impedance of the HV supplier network, [mΩ]
Q
2 2
Z = R + X
Q Q Q
Z Positive-sequence equivalent short circuit impedance referred to the low-voltage side of
Qt
the transformer
Z Impedance from the LV side of the upstream network (LV + MV) upstream the main
SUP
switchboard, [mΩ]
Z Impedance of the transformer, [mΩ]
T
2 2
Z = R + X
T T T
Z Impedance of line conductors upstream of the circuit being considered up to the main
U
switchboard, [mΩ]
2 2
Z = ( R + X )
∑ ∑
U line line
NOTE These impedances are shown in Fig 1
c Voltage factor according to IEC 60909
n Number of neutral conductors in parallel
N
n Number of protective conductors in parallel
PE
n Number of PEN conductors in parallel
PEN
n Number of line conductors in parallel
ph
x Reactance per metre of conductors, [mΩ / m]
ρ Resistivity of conductors at 20 °C, [mΩ·mm² / m]
0
ρ Resistivity of conductors at the maximum permissible steady-state operating temperature,
1
[mΩ⋅mm² / m]
ρ Resistivity of conductors at the mean temperature between steady-state temperature and
2
final short-circuit temperature, [mΩ⋅mm² / m]
ρ Resistivity of separate PE conductors at the mean temperature between ambient and final
3
short-circuit temperature, [mΩ⋅mm² / m]
θ Temperature, [ºC]
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Figure 1 – Examples of installation configurations and impedances used in this document
4 Parameters
4.1 General
Table 1 − Resistivity at 20 °C in accordance with IEC 60909, in mΩΩ⋅ΩΩ⋅⋅⋅mm² / m
Copper Aluminium
18,51 29,41
ρ
0
NOTE 1 For the conductor resistances when dealing with cables, Annex A may also be used.
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Table 2 − Resistivity at various temperatures
Thermosetting 90 °C
Thermoplastic 70 °C (PVC)
(EPR or XLPE)
Resistivity Temperature Resistivity Temperature
20 °C 20 °C
ρ 1,00 ρ 1,00 ρ
0 0 0
70 °C 90 °C
ρ 1,20 ρ 1,28 ρ
1 0 0
ρ 1,38 ρ 160+ 70
2 0
= 115°C
2
≤ 300mm²
250+ 90
= 170°
1,60 ρ 2
0
ρ 1,34 ρ 140+ 70
2 0
= 105°C
2
300mm²
>
ρ 1,30 ρ
160+ 30
3 0
= 95°C
2
≤ 300mm²
250+ 30
= 140°
1,48 ρ
0 2
ρ 1,26 ρ
140+ 30
3 0
= 85°C
2
> 300mm²
The above factors are obtained using the following equation:
ρ = ρ [1 + 0,004 · (θ - 20)]
θ 0
where
θ is the conductor temperature
Table 3 − Reactance per metre of conductors of cables ( x )
x
[mΩ / m]
Multicore cables
or single core cables in trefoil 0,08
arrangement
Flat touching single core cables 0,09
Flat spaced single core cables 0,13
NOTE 2 Values for armoured cable should be obtained from the manufacturer.
NOTE 3 The reactance values given are for single-line system, they can be used as average values for a three-line system.
NOTE 4 For spaced single core cables, the distance from centre to centre is assumed to be two times the overall cable
diameter.
NOTE 5 More precise values may be obtained from IEC/TR 60909-2 or from manufacturers.
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4.2 Conductor resistances
Conductor resistances per meter at 20 °C are given in Annex A.
For the calculations set out in this Technical Report, conductor resistances per metre for sizes up to
2
300 mm , may be obtained from the following equations:
Line conductor Neutral conductor Protective conductor
ρ ρ ρ ρ
0 0 0 0
R = R = R = or R =
c0ph c0N c0PE c0PEN
S ⋅n S ⋅n S ⋅n S ⋅n
ph ph N N PE PE PEN PEN
ρ ρ ρ ρ
1 1 1
1
R = R = R = or R =
c1ph c1N c1PE c1PEN
S ⋅n S ⋅n S ⋅n S ⋅n
ph ph N N PE PE PEN PEN
ρ ρ ρ ρ
2 2 2
2
R = R = R = or R =
c2ph c2N c2PE c2PEN
S ⋅n S ⋅n S ⋅n S ⋅n
ph ph N N PE PE PEN PEN
ρ
3
R =
c3PE
S ⋅n
PE PE
NOTE The current sharing has been considered as equal between several conductors in parallel. The current sharing may not
be equal between several conductors in parallel of large cross-section e.g. greater than 240 mm², hence simple division by the
number of conductors may not be suitable (see IEC 60287-1-3).
4.3 Conductor reactances
Conductor reactances per meter are obtained from the following equations:
x
Three-line or line to line X =
c
n
ph
x
Line to neutral (or PE or PEN) X =
cph
n
ph
x
X =
cN
n
N
x
X =
cPE
n
PE
x
X =
cPEN
n
PEN
NOTE 1 For conductors having a cross-sectional area of less than 25 mm², the reactance is much smaller than the resistance
and hence it can be ignored for the calculations set out in this Technical Report and made manually.
NOTE 2 Although it is usually convenient to consider the value of inductive reactance of each conductor of a earth fault
current loop separately as done in this Technical Report, such values do not truly exist as independent quantities, as inductive
reactance is a function of all the conductors in close proximity.
Consequently, the value of inductive reactance for a conductor is liable to be different for the various fault conditions (three-line
fault, line-to-earth fault, etc.) for which the conductor forms part of the earth fault current loop.
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SIST-TP CLC/TR 50480:2011
CLC/TR 50480:2011 - 16 -
5 Characteristics of installations
Table 4 − Selection of resistivity and reactance for insulated conductors and cables
INSULATED CONDUCTORS AND CABLES
RESISTIVITY REACTANCE
UPSTREAM CIRCUIT All
RULES CURRENTS CIRCUITS
CIRCUITS
Distribution circuits Final circuit circuits
I 3 Line x
ρ ρ ρ
k3 max
0 0 0
MAXIMUM SHORT-
I Line to line x
ρ ρ ρ
k2 max
0 0 0
CIRCUIT CURRENT
I Line to neutral x
ρ ρ ρ
k1 max
0 0 0
NATURE OF THE PROTECTIVE DEVICE Fuse Circuit Fuse Circuit
breaker breaker
I Line to line ρ ρ ρ ρ ρ x
k2 min
1 2 1 2 1
MINIMUM SHORT -
CIRCUIT CURRENT Line to neutral
I ρ ρ ρ ρ ρ x
k1 min
1 2 1 2 1
b a
Line to PEN / Line to PE ρ ρ ρ ρ ρ x
1 2 1 1 1
Line to reduced PEN /
b a
ρ ρ ρ ρ ρ x
1 2 1 2 1
Line to reduced PE
EARTH FAULT
I
ef
Line to separate PE:
CURRENT
for line x
...
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