Cables and Support Systems PDF

Cables and Support systems Components of cables Main, sub-mains and final sub circuits Cable support systems Fire resistance cables Busducts 1 Sheath is for cable protection Higher conductor size...

Cables and Support systems Components of cables Main, sub-mains and final sub circuits Cable support systems Fire resistance cables Busducts 1 Sheath is for cable protection Higher conductor size means cable can take more current Sheath Conductor Insulator Higher insulator size means cable can take higher voltage Sheath Conductor Insulator Cables & Cable Components A cable – an ‘insulated’ conductor. 3 main items make up a cable, namely – Conductor – Insulation, and – Mechanical protection. Insulation Conductor Mechanical Protection Insulation Conductor Single core PVC-insulated Three core XLPE/PVC copper cable copper cable 4  Conductor Size of the conductors, measured in mm2 – chosen according to current rating of circuit. Made of either copper or aluminium. S/N Aluminum Copper 1 Light weight Heavier 2 Big size Small size for the same current carrying capacity 3 Cheap Expensive 4 High resistivity Low resistivity 5  Conductor/Insulator Conductor Stranded, i.e. consists of many small wires, bunched & twisted neatly together. This will enable flexibility during installation. Size of conductor – total areas of all the individual cross- sections of the small wires, excluding air space. Insulators Insulator is the exterior covering of conductor. Prevents the live conductor from being touched. S/N PVC XLPE 1 For less than 3.3 KV For more than 3.3 KV 2 Operating temp upto 70 Upto 90 deg C deg C 3 Max 160 deg C Upto 250 deg C 4 Cheap Expensive 6  Other insulations Synthetic rubber –for high temperature upto 85 deg C for equipment such as heaters, lighting fittings. Silicone rubber – for special applications, covering –60oC to 150oC, e.g. hospital equipment (subject to sterilization) Magnesium oxide – found in Mineral Insulated Copper Covered (MICC) Cables. A type of fire cables. Operating temp of upto 250 deg C. Sheath Sheath is the final layer over the insulation. Protects the cable against mechanical damage. If possibility of damage is high (underground) armoured cables are used. 7  Color code New Color code Old Color code New scheme implemented in March 2009 After March 2011, compulsory to use new code 8  Single Core and Multi Core S/N Single Core Multi Core 1 Only one conductor set 3 or 4 sets 2 Common for large size Common for small size cables cables 3 Single phase – 3 cables – All – 1 cable L,N,E Three phase – 5 cables- Brown, Black, Grey, Blue, 9 Green/Yellow  Cable Specification 4C,120 mm2 Cu/XLPE/PVC /SWA/PVC + 70 mm2 Cu/PVC/CPC 3-phase cable (multi core) – Has 4 stranded copper conductors (4C) – Each core – cross-sectional area of 120 mm2. ‘XLPE/PVC’ : – Insulation is Cross-linked Polyethylene – Sheath is Polyvinyl Chloride. Separate earth cable (Circuit protective conductor -CPC), size 70 mm2 70 mm2Copper – has copper conductor & PVC insulation. 120 mm2Copper XLPE PVC - CPC PVC CPC – Circuit Protective conductor SWA – Steel Wire Armoured 10  Single & multi core cables 1. Conductors : Plain annealed stranded copper conductor 2. Insulation : Cross-linked PE compound 3. Filler (where applicable) : PVC or Polypropylene yarn 4. Binder Tape (where applicable) : Polyester (mylar) tape 5. Bedding (for armoured cable) : Flame retardant PVC, type ST2 or LSHF compound 6. Armouring (for armoured cable) : Aluminium wires or Galvanized steel wires 7. Oversheath : Flame retardant PVC, type ST2 or LSHF compound 11  Cable specification Multicore cable common upto 120 mm2 Beyond 120 mm2 single core cables are used as they are more flexible Submain cables carry large currents Final circuits carry small currents - Range 1.5 to 4 mm2 CPC cable size can be different from that of phase conductors, according to the requirements of CP5. E.g. If phase conductors are 120mm2, min size of CPC calculated to be 60mm2 non-standard size. As such, 70mm2 CPC shall be used. Cross-sectional area of phase Minimum Cross-section area of conductor CPC S ≤ 16 S 16 < S ≤ 35 16 S > 35 S/2 hcs/Rev01 Oct05 12  Selection of Cable size Cable Size Selection Current Voltage drop carrying capacity hcs/Rev01 Oct05 13  Current carrying capacity When size decreases, current carrying capacity decreases Cable Size In higher room temperature, current carrying capacity Ambient Temp decreases In an enclosed environment, current carrying capacity decreases Installation factor When more cables are around, current carrying capacity decreases Grouping factor hcs/Rev01 Oct05 14  Selection of Cable Size Current Carrying Capacity - Cable Size - Ambient Temperature (Cannot dissipate heat) - Installation factor (insulated wall) - Grouping factor (Several cables heat removal rate is less) Design must be based on CP5 If Size is small – High heat, insulation damage, short circuit, fire, cable insulation can degrade slowly. If size is big – Waste of money. Standard – 1.5 mm2 for lighting 2.5 mm2 Power socket 15 Guide from CP5 16 What happens if a cable is inadequately sized? Temp of conductor increases too high such that: – cable insulation breaks down, – a short circuit or worse, – a fire may result. Cable insulation will degrade slowly over time due to overheating. 4 mm2 cable IFL = 35A ! 1-phase Overheating Equipment used has a a.c. source occurs as IFL > current carrying capacity (CCC) CCC of cable!!! of 32A. Figure 5.4 17  Voltage Drop Equipment voltage operating range: – 230V ± 10% for single phase – 400V ± 10% for 3-phase. Supply Voltage range: – 230 or 400V ± 6%. Therefore, volt drop along cable: – 4% “from the origin of the installation e.g. the supply terminals) to the socket outlet of the terminals of the fixed current-using equipment” Power Supply Equipment +/- 6% +/- 10% Voltage drop allowable 4% 18  207 – 253 volts Main DB Televison 230 V 195 V 207 – 253 volts Main DB Televison Use thicker cable 227 V 230 V 207 – 253 volts Main DB Televison 230 V Reduce length 228V hcs/Rev01 Oct05 19  Example 1 - Question A 3-phase lift equipment system having a full load current of 20A is supplied by the MSB located at the ground floor 60m away. The equipment must comply to the voltage regulation of Singapore. – If the cable resistance is 13mΩ/m, can this equipment still function under extreme conditions of supply voltage? – What happens if the ambient temperature in the electrical riser increases, and the cable resistance is now increased to 14.5 mΩ/m? 20  Example 1 - Answer Cable Resistance – R = 13 x 10-3 x 60 = 0.78 Ω. Actual Cable Drop – Vd = I R = 20 x 0.78 = 15.6V or 3.9%. Therefore, OK but just OK. 21  Example 1 - Answer Ambient temp  If the resistance  to 14.5 mΩ/m, – Cable Resistance R = 14.5x10-3x60 = 0.87 Ω. – Actual Cable Drop Vd = I R = 20 x 0.87 = 17.4V or 4.35%. Not acceptable! Not complying to regulation! Equipment may not function properly. 22  Cable Support Cable ladder for large cables Cable trunking for smaller Cable conduit for final cables, final circuits hcs/Rev01 Oct05 circuits 23  Installation details for socket outlets G.I or PVC Conduit Concealed Conduit Concealed Junction Box Switch Socket Outlet Face Plate Flushed Mount Switched-Socket Outlet Surface Mount Switched-Socket Outlet 24 CP5 states that all wirings within a wall shall have adequate mechanical protection  Cable support system installation Socket/Telephone Outlet 3 channel Flush Floor Trunking Screed Concrete Slab Metal Anchor Fasteners Metal Trunking Wiring Cables Cable Tray or Ladder ‘L’ Shape Bracket Cables Metal Rod & Support Channel 25  Fire Retardant Cables Emergency equipments must continue to operate even in case of fire. Sprinkler pumps, Emergency lights, Smoke Extraction fans, Fireman lift Similar construction But have an additional Fire resistant Layer (Mica or Magnesium oxide) Three-phase FR cable Single-phase FR cable 26  Fire Retardant cables Exhaust fan Fire man Lift Sprinkler Pump hcs/Rev01 Oct05 27  MICC & Mica-taped FR Cables CWZ cable Cat CWZ is a fire resistance test: – C: cable remains conductive at a temp of 950oC for 3 hours, – W: under water-spray condition and – Z: under mechanical shock impacts. 28  Functions of Busducts Same function as cables i.e. for conducting electricity But: busducts combine conductor, insulation, mechanical protection and support system all into one entity. Benefits: – Smaller in physical size at high currents typically used for 1500A to 3000A. – Low resistance as conductors are made of solid copper. – Flexibility in allowing tap-off supply 29 conveniently when required.  Busducts Busbar bending http://www.youtube.com/watch?v=GT_ELoyLaHI Busduct installation http://www.youtube.com/watch?v=04cphQiJjNU hcs/Rev01 Oct05 30  Busducts Busducts combine Conductor, Insulation, Mechanical Protection and support system all into one entity. S/N Cables Busducts 1 Big size Small in physical size (for the same current) 2 Higher resistance Low Resistance 3 Not Flexible Flexibility to tap-off supply conveniently 4 Cheap Expensive Good for High rise Offices, Shopping centres, Factories. High cost and only custom made 31  Busducts in factories Horizontal busducts run extensively at high level Droppers provided at locations where power is required, (either direct connection to machinery or thru DB) 32 Busducts in factories 33 Cable Tray Summary 1 Cable Conductor Insulation (PVC and XLPE) Sheath Color Identification Single Phase – Red, Black - Old Brown, Blue - New Three Phase – Red, Yellow, Blue and Black (Neutral) - Old - Brown, Grey, Black and Blue (Neutral) - New Cross Sectional Drawing 1X 4C, 120 mm2, Cu/XLPE/PVC + 70 mm2Cu/PVC CPC 4 X 1C, 300 mm2, Cu/PVC/SWA/PVC + 150 mm2/Cu/PVC/CPC Current Carrying Capacity Cable size Ambient temperature Installation factor Grouping factor Inadequate Size Temperature increase Insulation Degradation Possibility of fire 35 Summary 2 Voltage Drop V=I*R Equipment tolerance +/- 10% Supply voltage +/- 6% Voltage drop allowed 4% Support Systems Cable ladder or tray Trunking Conduit Mounting Surface Flush/Recessed Fire retardant cable Fire barrier between conductor and insulator MICA or Magnesium Oxide CWZ Conductive at temperature > 950 deg C Under water spray condition Under mechanical shock impact 36 Summary 3 Busducts Conductor Insulation Mechanical Protection Support systems Advantage of Busducts Small in size for high currents Low resistance Flexibility Ease of Installation Disadvantages High cost Custom made 37