Upload
acadennis
View
57
Download
1
Tags:
Embed Size (px)
DESCRIPTION
BS7671 17th Ed Draft 1 Part 6
Citation preview
1BS7671 2008 Outcomes AppendicesUse of appendices
8.1 Apply relevant information/data within Appendices A: British Standards to which reference is made in the Regulations B: Statutory regulations and associated Memoranda C: Time/Current characteristics of overcurrent protective devices D: Current-carrying capacity and voltage drop for cables and flexible cords E: Classification of external influences F: Electrical Installation Certificate, Minor Works Certificate and Periodic
Inspection Report G: Harmonized cable core colours H: Current-carrying capacity and voltage drop for busbar trucking and
powertrack systems i: Definitions other systems J: Protection of conductors in parallel against overcurrent K: Effect of harmonic currents on balanced three-phase systems L: Voltage drop in consumers installations M: Methods for measuring the insulation resistance/impedance of floors and
walls to earth or to the protective conductor N: Measurement of fault loop impedance: consideration of the increase of the
resistance of the conductor with the increase of temperature O: Ring and Radial final circuit arrangements
2BS7671 2008:AppendicesAppendix 1 has new and adapted BS EN numbers and associated
harmonized documentation
BS7671 2008 appendix 1
Appendix 2Relationship between statutory bodies
Distributors systems ESQC Regs. 2002
Buildings The building regs. 2000
Non domestic places of work activity EAWR 1989
Cinemas Cinematography regs 1955
Machinery Supply of machinery 1992
Entertainment and theatres Conditions of licence miscellaneous 1982
HV lighting As above
5Appendix 3Appendix 3 differs in that:16th ed :
17th ed :
The Nominal Open Circuit Voltage is now 230V
BS3871 Type 2 MCBs are no longer included
Maximum Zs Tables in Part 4 have been adjusted to take into account 240 -> 230V
IaUZ OS
IaUZ OCS
Appendix 3New table, 3A, Time/current characteristics for BS EN
61008/9RCD Type
INmA mA
Trip time ms mA
Trip time ms mA
Trip time ms
General Non-delay
G type
10 10 300 max
20 150 max
50 40 max
30 30 60 150
100 100 200 500
300 300 600 1500
500 500 1000 2500
DelayS type
Selective
100 100 130 min500 max
200 60 min200 max
500 40 min150 max300 300 600 1500
500 500 1000 2500
NI1 NI2 NI5
Instantaneous tripping assume the fastest time, 0.1sec is given here, see manufacturers data sheets for faster and more accurate times
8BS7671 2008:Appendices
Appendix 4 : A new contents page with additional tables (4A3) Methods of installation of cables have changed from
numbers to lettersExamples: 1. M4 -> A, 2. M3 -> B, 3. M1 and M11 -> C Specific methods for Domestic installations (100, 101,
102: applicable to table 4D5)New formula to assess grouping factor in enclosures
Where F is the de-rating factor; n is the number of grouped cables
n1F
9BS7671 2008: Appendix 4
Simple chart outlining installation methods
BS7671 2008: Appendix 4Example of install methods for twin and earth
11
BS7671 2008: Appendix 4New tables for grouping and ambient temperature,
buried in the ground
Appendix 4
Appendix 4
Appendix 4
15
BS7671 2008: Appendix 5Appendix 5 has the same structure and content as the 16th editionDifferences are:IP ratings (characteristics of installation) are now includedBS EN cross referencing is now included
Appendix 6
ADS
Appendix 6 Model forms of certificationNo changes here except definitions within the Schedule of inspections
17
Appendix 7Appendix 7 : Harmonized colour coding of conductors
18
BS7671 2008: Appendix 8
Powertrack and busbar systemsA preassembled trunking with ridged
copper bars on fixed supports allowing connection to be made at predetermined intervals via a fused plug socket arrangement.
Appendix 8Calculations for effective current carrying capacity follow the
general requirements for :
1. Protection against shock (41)2. Thermal Effects (42)3. Overcurrent and overload protection (43)4. Volt drop (525), app 12, para 5 app 8
20
BS7671 2008: Appendix 8
Current carrying capacity = In (?)Ambient temp = 35CCorrection factor for ambient temp. > 35C = KCorrection factor for angle of mounting = KEffective current carrying capacity under new mounting
conditions and higher than ambient temp. = IzTherefore Iz => In x K x KIz => Ib where Ib = design currentIa In where In in this case is the rating of the OPDVd = (mV/A/m x L x Ib) / 1000 V
21
BS7671 2008: Appendix 9
Multiple supplies DefinitionsOutlining methods of earthing with or without NeutralsExample: An AC TN-C-S system
Appendix 9TN-C-S DC system, earthed midpoint conductor M and protective conductor is combined in one single conductor as part of the installation
Reg 8(4) of the Electricity, Safety, Quality and continuity regs 2002 states that a consumer shall not combine the neutral and protective functions I a single conductor in the consumers installation
23
BS7671 2008: Appendix 10
Conductors in Parallel protection against overcurrentUsed to supply greater currents than the max current
capacity of a single conductordomesticObvious example might be a ring final circuitIndustrialFeeders where multiple singles are used or trefoil 3 phase conductors are laid in parallel
(reduces the effects of reactance)
BS7671 2008: Appendix 10Overload protection
Appendix 10Overload protection
BS7671 2008 UpdateShort Circuit Protection
Appendix 10Short Circuit Protection recommended methodIf one conductor is damaged then all three are disconnected
Appendix 11 - Harmonics in 3-phase systems
Harmonic distortion is the change of the supply voltage from the ideal sinusoidal waveform
Caused by:Interaction of distorting customer loads with the change in supply
network impedancePrimary effects are:1. Overheating of induction motors, 2. Overheating of transformers, 3. Damage to PF capacitors4. Overloading of neutrals5. Interaction of harmonic currents with power factor
correction capacitors causing gross amplification through resonance and serious damage to system components
BS7671 2008: Appendix 11Harmonics on Balanced three phase systemsFor higher frequency harmonics with conductors < 50mm2 use the
formula:
Use table 11 for 3rd harmonic as shown in examples
Appendix 11Application of rating factors for triple harmonic currents
Appendix 11
Application of rating factors for higher frequency harmonic currents
Apply formula to following example
A 3 phase 30kW 0.85 pf VSD machine contains within its line currents 45% 3rd harmonic, 30% 5th harmonic, 20% 9th harmonic and 15% 12th harmonic currents calculate the correction factor/s to be applied to the conductors
2
LLL
80Harmonicsth12,th9,th5
Harmonicth12Harmonicth9Harmonicth5
A8086.0
345.051Harmonicrd3
A5185.0400732.1
000,30Ipf.I.V.3P
32
BS7671 2008: Appendix 12
Volt Drop in consumers Installations
BS7671 2008: Appendix 13
Insulation of floors and walls (from GN3)Taken from GN3 Inspection and Testing
BS7671 2008: Appendix 14
Temperature effects on the Earth Loop Impedance (GN3)
)3.412.41tablemax.Zs(IU8.0mZ
A
OS
0.8 adjusts for actual operating conditions such as ambient temperature at the time of fault and the operating temperature of the cable while the fault is in progress.
35
Annex to Appendix 14
Calculating Earth Fault Impedances
From OSG table 9A, 9B, 9C = The external impedance found by enquiry not
recommended or by measurement By enquiry TNS = 0.8, TN-C-S = 0.35, TT = 21 By Measurement: TNS < 0.8, TN-C-S < 0.35, TT 1667
- 200 max BS7671 100 NICEIC All installations RCD protected!
By calculation: As for final circuit calculations plus manufacturers data plus GN6 protection from overcurrent
Total earth-fault loop impedance:
MLmmRR /)21(
MLRRZeZs )
100021(
January 08 Legh Richardson 36
Annex to Appendix 14 Calculating Prospective Earth Fault Currents
Appendix 3, Section 411, 434 For the protective device to operate correctly the
open circuit voltage at the source of supply must be taken
From Appendix 3 time current characteristics for standard protective devices show the minimum fault current needed to operate the protective device and disconnect the circuit within the time to comply with BS7671
ZsUoIa
Appendix 15
BS7671 2008 Appendix 15
Standard Circuit Arrangements for Ring final and Radial circuits
Standard ring final circuit = 2.5mm2 per legStandard Circuit Arrangements for rings and radialsRing final circuit designed for 2.5mm2 live conductors and 1.5mm2
for CPC 433.1.5Starts and finishes at the Dist Board1.5mm2 can be used only if connected on the load side of a SFCU as
a spurSockets must share the loading equally spaced around the ringNo Space heaters and/or Immersion heatersCookers and other appliances (?) > 2kW prohibited2.5mm2 conductors for non-fused spursFloor area < 100m2
Appendix 15
BS7671 2008 Appendix 15
Standard Circuit Arrangements for Radial Circuits Applies to Twin and Earth BS6004 2.5mm2 = 20A OPD, serves an area of 50m2 4.0mm2 = 32mm2 OPD, serves an area of 75m2 4.0mm2 can have 2.5mm2 non fused spurs serving one DSSO 4.0mm2 can have 1.5mm2 fused spurs serving one DSSO