IET Lecture - LV Circuit Design September 2014

Cable Sizing Fundamentals and E l e c t r i c a l LV S t a n d a r d Armada Hotel, Petaling Jaya 2 3 rd A u g u s t 2 0 1 4

Cable Sizing For Safe Power System Based on IEC Standards I r . H . P. L o o i ( m e k t r i c o n @ g m a i l . c o m ) B.Eng (Hons), FIEM, Jurutera Gas

Part

1

–Circuit

Design

2

SYNOPSIS

‘Cable sizing is a fundamental skill set required of the design engineer. Unfortunately the theory and empirical basis on which cable sizing rest on is not well understood amongst practicing engineers. Such gaps in knowledge may have implication in the design of wiring systems particularly on the safety of wiring systems (particularly thermal safety). This Presentation provides an introduction to basic concepts in sizing of cables in electrical (LV) system based on the IEC standards. The presentation is based on the handbook published and is in the following logical procession: 1.

Introduction

2.

Scope

3.

General Design Procedure (design road map)

4.

Earthing system

5.

Cable types & installation method

6.

Circuit configuration 23 r d August 2014

7.

Conductor sizing

3

THE SPONSOR – WIRING HANDBOOK

‘The International Copper Association Ltd. (ICA) is a non-profit organization promoting the use of copper worldwide . ICA increases awareness and usage of copper by communicating its unique attributes as a sustainable element an essential to life, science and technology, and a higher standard of living. ICA Southeast Asia established by ICA in 1992 acts as a strategic and networking base for regional copper and associated industries’ associations.

This handbook is distributed FREE courtesy of the sponsor 23 r d August 2014

5

INTRODUCTION – ROAD MAP TO IEC60364

Protection Device

Load Estimation

Cable Selection L.V. Wiring Design

Circuit Configuration

Installation Method

Earthing Verification Equipment Selection

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8

VOLTAGE STANDARD

Malaysian Standard Voltages It is a misconception that Malaysia Standard Voltage is at 415V/240V !

As of 1st January 2008, Malaysia Standard Voltage is declared at 400V/230V Refer ST link for the official notification.

Rationalisation of voltage is to bring Malaysia in line with other member countries of the IEC. Singapore and the UK has already converted to 400V/230V from the old 415V/240V. Other IEC member countries which have yet to convert are Germany / China (380V/220V) and India (415V/240V). Practitioners must therefore design power distribution system to 400V/230V. 23 r d August 2014

9

VOLTAGE STANDARD

Malaysian Standard Voltages at 400V/230V +10%, -6% Electrical power distribution system should be designed to 400V/230V !  Change all reference in specifications to 400V/230V.  Specify transformers at nominal 11kV/420V (not 11kV/433V).  Check cable sizing as 400V/230V incur about 4% higher current.

Major reasons for rationalising to 400V/230V Standardisation among IEC countries. Multiple certification due to different voltage levels is avoided or minimised. Most motors and fluorescent light fittings works most efficiently within the voltage band of 210V to 220V. Thus reducing to 220V will  Save energy  Prolong life-span of electrical equipment. 23 r d August 2014

10 VOLTAGE STANDARD

Version 3 Published in 2013! 23 r d August 2014

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11 THE DESIGN WORK FLOW

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13 EARTHING SYSTEM 60364 - Part 1; 312 – 2 Letters definition:

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14 EARTHING SYSTEM

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15 EARTHING SYSTEM Network / Operation Criteria Service Criteria

System Chosen / Preferred

Competent Maintenance

Continuity of service critical

Available

IT System preferred

Continuity of service critical

Not consistently available

No satisfactory solution IT system preferred as discriminitive trippings are easier to implement and damages less with respect to TN system

Continuity of service NOT critical

Available

TN-S system preferred (rapidrepairs and extension easily performed.

Continuity of service NOT critical

Not available

No satisfactory solution. IT system preferred.

Fire hazard critical

Available

IT system and use of 5mA RCD or TT system preferred.

Special feature, very long networks

Assumed available

TT preferred

Special feature, standby power supply

Assumed available

TT preferred

Special feature, load sensitive to high currents (e.g. motors)

Assumed available

TT preferred; IT can be acceptable

Special feature, low natural insulation (furnace) OR very large HF filters (computers)

Assumed available

TN-S preferred

Special feature, control and monitoring systems

Assumed available

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IT for continuity of services; TT for enhanced equipotential

16 EARTHING SYSTEM – SIZING OF P.E. (TT)

60364-5-54, 312 : For TT system, PE need for exceed 25mm² (copper) 35mm² (aluminium)

As TT system effectively DO NOT have PE cables within the distribution system, this may presumably mean the earth electrode or frame earth system.

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17 EARTHING SYSTEM – SIZING OF P.E. (TNS) 60364-5-54, 543 For TN-S system (method 1): Cross sectional areas of line conductors S (mm²)

If the protective conductor is of the same material as the line conductor

If the protective conductor is not of the same material as the line conductor

S < 16

S

K1/K2 x S

16 < S < 35

16 a

K1/K2 x 16

S > 35

Minimum cross sectional area of the corresponding protective conductor (mm²)

S/2

a

K1/K2 x S/2

Where K1 is the value of k for the line conductor, selected from table A54.1 or from the tables of IEC50364-4-43 according to the resistance of the conductor and insulation. K2 is the value of k for the conductor selected from tables A 54.2 to A54.6 as applicable a

for a PEN conductor the reduction of the cross section area is permitted only in accordance with the rules for sizing of the neutral conductor (see IEC 23 r d August 60364-5-52).

2014

18 EARTHING SYSTEM – SIZING OF P.E. (TNS) 60364-5-54, 543 For TN-S system where the protective device afford disconnecting time NOT exceeding 5 seconds, the following formula may apply:

S = PE size (mm²); I = prospective fault current rms; t = operating time of protection device; k = factor based on conductor material and insulation.

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19 EARTHING SYSTEM – SIZING OF P.E. (TNS) 4x16mm² PVC + 1x16mm² PVC (PE)

Case :

SCI=10kA

Calculating I² t for PE:

70°C PVC cables

30A CB

k= 115

30A MCB class C, trip time

SC I=

3 kA

5 kA

6 kA

10 kA

15 kA

25 kA

t=

0.1 s

0.01 s

0.01 s

0.01 s

0.01 s

0.01 s

8.25

4.3

5.2

8.7

13.0

21.7

0.01 s

0.01 s

0.01 s

0.01 s

0.01 s

0.01 s

2.61

4.3

5.2

8.7

13.0

21.7

S min size of PE cable (mm²) 32A gG Fuse, trip time S min size of PE cable (mm²)

t=

From the above, we note that for up 15kA rating table 54.3 sizing for PE cable will be acceptable in terms of “energy-let-through” for both gG fuses and MCB class C and B types. 23 r d August 2014

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21 CABLE TYPES Cable types and installation methods have implication for cable sizing and Ampere capacity. IEC60364-5-52 : Cable Selection can be summarised:

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22 CABLE TYPES – ASSESSING CONDITIONS Part 5-51 defines environmental classes for use in defining installation and equipment selection criteria:

A A 2 Number – severity index 2nd alphabet – Specific conditions

A = Environment B = Utilisation C = Building

Specific conditions of environment usage etc are coded. Later prescription in standards specify technical conditions concerning conditions code.

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23 CABLE TYPES – ASSESSING CONDITIONS

External influences

Selection considerations

AA4, and AA5

Normal cable insulation PVC, or XLPE

AD5 to AD7

Ambient temp. -5ºC to +40ºC Presence of water

AE5 and AE6

Dusty atmosphere

AG3

Mechanical stress

AH2

Vibrations

AM1

Harmonics

Cable jointing glands to be IPX5 and better, extruded inner sheath for cables for AD7 (submerged) Cable jointing glands to be IP6X, bare conductor on insulator not recommended. Underground cables, mechanical protection of cables, sheathing of cables, armouring of cables, cable in ducts Connections to motor; termination lugs, cable slack to allow for vibration Mitigations for harmonics; Annex D in 60364-5-52 23 r d August 2014

24 CABLE TYPES – ASSESSING CONDITIONS

External influences

Selection considerations

AN3

Solar radiation

AP3 and AP4

Seismic effect

BD2 and BD4

Emergency evacuation; difficult exit Fire risk

Cable sheath or insulation which are immune against UV radiation (PVC sheath or insulation not permitted). Cable tray preferred over conduit, slack in cable run etc. Low smoke (LSZH) cables

BE2 CA2 CA2 and BE2

Presence of combustibles Combustibles and explosion risk

Fire rated cables for essential services; LSZH cables Fire rated cables for essential services; LSZH cables Design to IECEx standard IEC 60079 series. 23 r d August 2014

25 CABLES FOR FIRE & SMOKE CONDITIONS Flame retardant cables do not promote or propagate the spread of fire. Flame retardant cable installation is specified under conditions of emergency evacuation (BD2 and BD4 external influences). These conditions of emergency evacuation also apply in building spaces designated as fire escape routes or emergency evacuation routes under “life safety” standards for building design.

The ‘degree’ of flame retardant required will depend on the designed ‘evacuation-time’ of the escape routes. The test for compliance to flame retardant properties are defined in the IEC 60332 series:  IEC 60332-1 & 60332-2; flame propagation test on single cable is the most basic flame retardant test (whilst Part 1 specify 1kW flame for general insulated cables, Part 2 specify ‘diffuse’ flame for single insulated small cables);  IEC 60332-3; specify more stringent flame propagation test on bunched cables.

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26 CABLES FOR FIRE & SMOKE CONDITIONS

Low Smoke, Zero Halogen (LSZH) cables reduces smoke with zero halogen emission. Classes of cables listed as Low Smoke Flame Retardant (LSFR) or Low Smoke Zero Halogen (LSZH) are defined by the following test standards:  The test for Low Smoke is the smoke density test of IEC 61034;  The test for halogen emission is specified in IEC 60754-1; and  The test for degree of acidity of is specified in IEC 60754-2.

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27 CABLES FOR FIRE & SMOKE CONDITIONS Fire Resistant (FR) cables can maintain circuit integrity even in the presence of a fire. The test for fire resistive behaviour is specified in IEC 60331 fire integrity tests. FR cables are mandatory where essential services (e.g. fire fighting services, fire lifts etc) require ‘circuit survivability’ even during a fire emergency). 1. LSFR, LSZH sheath 2. Binder tape 3. Filler, non-hygroscopic

4. Insulation, XLPE-FR 5. Mica tape (fire resistant barrier) 6. Conductor, solid or stranded.

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28 CABLES FOR FIRE & SMOKE CONDITIONS

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29 CABLES FOR FIRE & SMOKE CONDITIONS

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30 CABLE TYPES

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31 CABLE TYPES – COMMON DEFECTS Conductors and cables

Bare conductors

Insulated conductors

Sheathed cables (including armoured and mineral insulated) Multi core Single core  NA    

Method of Installation

Without fixings   Clipped direct   Conduit systems   Cable trunking systems (including skirting trunking, flush floor  1   trunking) Cable ducting systems     Cable ladder, cable tray,     cable brackets On insulators   NA NA Support wire      – permitted  – not permitted NA – not applicable or not normally used in practice 23 r d August 2014 Table 5A – Cable installation method and cable types from IEC 60364-5-52

32 CABLE TYPES – COMMON DEFECTS Some Common Defects 1. PVC conduit system are substandard and are NOT certified to electrical grade. 2. PVC conduit and/or cables laid in condition where continuous sunlight occurs (PVC will deteriorate in the presence of UV light). 3. Conduit embedded in concrete are of the wrong grade (conduit not properly graded will crack when laid in concrete).

4. No proper junction boxes and/or terminal boxes. 5. Trunking and/or conduit ‘overloaded’. 6. Splicing/jointing of cables without proper terminal box.

No proper evaluation on firerating of cables in complying with fire properties.

PVC products should NOT be installed exposed to sunlight. 23 r d August

2014

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34 CIRCUIT CONFIGURATION – EARTHING

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35 CIRCUIT CONFIGURATION

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36 CIRCUIT CONFIGURATION

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37 CIRCUIT CONFIGURATION

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38 CIRCUIT CONFIGURATION

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39 CIRCUIT CONFIGURATION

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40 CIRCUIT CONFIGURATION

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Cable Sizing Fundamentals and E l e c t r i c a l LV S t a n d a r d Armada Hotel, Petaling Jaya 2 3 rd A u g u s t 2 0 1 4

Cable Sizing For Safe Power System Based o n I E C S t a n d a r d s I r . H . P. L o o i ( m e k t r i c o n @ g m a i l . c o m ) B.Eng (Hons), FIEM, Jurutera Gas

Part

1

–Circuit

Design

Intermission-Continue to Part 2,,,