10 common practice issues (mistakes) by design (electrical) engineers May 2011....
25 Common Problems for M&E Engineers Armada Hotel , Petaling Jaya 26th May 2011
10 Common Electrical Design Problems – Part II Ir. Looi Hip Peu Hon Sec, ACEM (2010/11) B.Eng (Hons) (Electrical) P.Eng (5226), Jurutera Gas
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CONTENT
2
Objectives of this Workshop
System Design
Wiring Design
Protection
Installation
1. Tariff selection
3. Earthing system
7. RCD selection
9. Standards
2. Generator sizing
4. PE cable selection
8. Motor starting
10. Malaysian wiring code
5. Mains cable sizing 6. Al vs Cu cables
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Aluminum & Copper Cables
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WIRING DESIGN – AL & CU CABLES
C u r r e n t l y t h e m a r ke t f o r c o p p e r i s u n s t a b l e and copper price has become high. This has affected the demand for copper cables with Clients and contractors requesting designers to change from copper to aluminum cables. What are the possible impact on design, cost and future operation. Is AL cables a fire hazard? Unfortunately professional engineers faced with such request cannot brush them off easily due to the cost implication neither can they satisfactorily answer their clients.
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WIRING DESIGN – AL & CU CABLES
Properties of Material Material
Thermal expansion, at 25 °C µm-m-1 K-1
Volumetric coefficient, β, at 20 °C (10−6/°C)
Electric Resistivity ρ [nΩ·m] at 20 °C
Melting Point
Aluminum
23.1
87
28.2
933 °C
Copper
16.5
51
16.8
1084.6 °C
Steel
17.3
51.9
~ 100
?? °C
AL has higher coefficient of expansion A L h a s a h i g h e r e l e c t r i c r e s i s t i v i t y. A l c a b l e s i z e w i l l have to be one size larger
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26th May 2011
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WIRING DESIGN – AL & CU CABLES
Possible hazard for Copper Cables
Galvanic reaction between AL and copper terminals. Proper AL-Cu terminals will be required. Al has a higher coefficient of expansion. Cable connections may loosen in the long run. AL wiring not properly installed is a fire hazard mainly due to loosening connections at terminals. AL subject to galvanic reaction with copper and steel terminals.
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26th May 2011
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WIRING DESIGN – AL & CU CABLES
Best Practice for AL cabling systems A l l c a b l e s < 7 0 m m ² s h o u l d b e c o p p e r. I n d i a h a s t h e m o s t ex p e r i e n c e i n u s i n g A l c a b l e system inbuilding. In India the rule of < 70mm² to be copper holds. Cables used outdoor may be AL. Proper cable connectors at terminals should be used. Al cable terminations and connectors are recognised as a major cause of fire from overheating. Al cabling system should be subject to annual check of cable terminations.
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26th May 2011
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WIRING DESIGN – AL & CU CABLES
Conclusion 1. Engineers should ensure proper terminations and cable bimetal joints/lugs are used. 2. Practitioners should properly advise client and property manager on the need for regular check due to risk of fire hazard from AL cable terminations.
3. Cost savings in AL cables may have consequences for maintenance!
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Re s i d u a l C u r r e nt D e v i c e s ( R C D )
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RCD
Residual Current Devices are essential items in wiring design. However with the widespread use of electronic loads, spurious/intermittent tripping by RCD are a b a n e f o r t h e d e s i g n e n g i n e e r. 1. Understanding RCD.
2. RCD design for electronic
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26th May 2011
RCD
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Common terms confused with RCD: RCD – class of protection device measuring residual currents ELCB – Earth Leakage Circuit Breaker 2 types (i) Voltage ELCB & (ii) Current ELCB. IEC coined the term RCD to refer to i-ELCB so as to differentiate it from vELCB
RCCB – Residual Current Circuit Breaker refers to RCD fitted with or to a circuit breaker e.g. RCD fitted to socket outlet with breaker to disconnect outlet woul be a RCCD. RCBO – Residual Current Breaker with Overcurrent refers to RCD fitted with O/C device e.g. RCD fitted to MCB or MCCB. GFI – term used in North America for RCD.
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RCD
Types of RCD
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RCD
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RCD Despite its reputation for protection; the biggest problem afflicting RCD is spurious tripping. Most spurious/intermittent tripping can be resolved either due to choice of RCD or design issues in network. Common response: remove/disable RCD; Replace with a less sensitive RCD BOTH METHODS ARE DANGEROUS AND SHOULD BE AVOIDED!
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RCD
IEC 62350 – GUIDANCE FOR THE CORRECT USE OF RESIDUAL CURRENT OPERATED DEVICES (RCDs) FOR HOUSEHOLD AND SIMILAR USE.
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RCD
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Best Practice RCD
Choose the right RCD for the right kind of load: Type A
Loads 1, 4, 5, 8
Type AC
Loads 8 & 9
Type B
Loads 1 - 9
Estimate leakage current of loads and select sensitivity of RCD
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Motor Starting
26th May 2011
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PROTECTION – MOTOR STARTING
Protection Relay Motor Starting
Many reasons phenomenon:
can
ke e p s
tripping
on
be
attributed
to
this
Mechanical system issues Mismatch in protection device and motor starting surge.
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PROTECTION – MOTOR STARTING
SELECT TRIPPING CURVE OF PROTECTION RELAY TO TAKE INTO ACCOUNT STARTING SURGE.
IDMT CURVES
NORMAL INVERSE VERY INVERSE EXTREMELY INVERSE
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PROTECTION – MOTOR STARTING
SELECT TRIPPING CURVE OF PROTECTION RELAY TO TAKE INTO ACCOUNT STARTING SURGE. Choose curve 3
IDMT CURVES
NORMAL INVERSE VERY INVERSE
Motor starting surge
EXTREMELY INVERSE
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26th May 2011
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M a l ays i a n W i r i n g S t a n d a rd s
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9 INSTALLATION – MALAYSIAN STANDARDS
Currently specification of consultants are not updated to reflect actual update. Some of the update are mandatory under Malaysian laws.
L.V. Distribution System MSIEC 60364 – Electrical Installation in Building (Part 1 to Part 7).
(note: IEE 17th edition or BS7671 us NOT the preferred wiring code. MS 1979:2007 "Electrical Installation of Buildings – Code of Practice" MS 1936:2006 :Electrical Installation of Building – Guide to MS IEC 60364"
Malaysian Voltage is 400V 3phase/230V 1phase +10%, -6%
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9 INSTALLATION – MALAYSIAN STANDARDS
Power Quality and EMC PQ MS1760:2004 and IEC 61000-2-8; Definition of PQ phenomenon (surge, dip, transient). MS-IEC 61000-4 Mitigating factor for PQ & immunity levels EMC IEC 61000-1-1; definition of EMC, classification of EMC phenomenon (conducted LF, radiated LF field, conducted HF, radiated HF field, electrostatic discharge, HEMP). IEC 61000 introductory level only of Part 2 (EM Environment), Part 3 (emission /immunity limits) and Part 4 (testing and measurement techniques). IEC 61000- Part 5-1; Understanding EMC mitigating concepts under Part 5; EM coupling, emitter and susceptor, mitigating EM disturbance (identifying EM class, zone protection, earthing etc.) Part 5-2 mitigating EMC; earthing and cabling.
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9 INSTALLATION – MALAYSIAN STANDARDS
Power Quality and EMC PQ MS1760:2004 and IEC 61000-2-8; Definition of PQ phenomenon (surge, dip, transient). MS-IEC 61000-4 Mitigating factor for PQ & immunity levels EMC IEC 61000-1-1; definition of EMC, classification of EMC phenomenon (conducted LF, radiated LF field, conducted HF, radiated HF field, electrostatic discharge, HEMP). IEC 61000 introductory level only of Part 2 (EM Environment), Part 3 (emission /immunity limits) and Part 4 (testing and measurement techniques). IEC 61000- Part 5-1; Understanding EMC mitigating concepts under Part 5; EM coupling, emitter and susceptor, mitigating EM disturbance (identifying EM class, zone protection, earthing etc.) Part 5-2 mitigating EMC; earthing and cabling.
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9 INSTALLATION – MALAYSIAN STANDARDS
Energy Efficiency
MS1525 – Energy Efficiency for Electrical Engineer Lightning Protection MS IEC 62305 Protection Against Lightning
MS IEC 61662 ; Assessment of the Risk of Damage Due to Lightning. Fire Protection For Electrical Engineers MS 1745 Fire Alarm and Detection System
BS5839 Part 8 and 9 (Emergency call system) Voice and Data Networks (telecom works) “Technical Standards, Infrastructure Requirements” (TSIR, issued by MCMC).
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M S 1 9 7 9 M a n d a to r y W i r i n g C o d e
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INSTALLATION – MS 1979
Many practitioners are still unaware of Malaysian Standards pertaining to Wiring Installation which are mandatory. Common citation in specifications is the IEE 17th (and even 16th edition (correctly known as BS7671)
The structure of MS1979 is a simple distillation of all the important prescriptions contained in MSIEC60364 which have direct relevance to wiring in residential buildings. Rule-based conditions are set-out in the MS1979 where only performance-based requirements are listed in the MSIEC60364. The final product is a very simple booklet containing individual "COP" (Code Of Practice) numbered COP1 to COP91.
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INSTALLATION – MS1979
Briefing summary of prescription COP05 – All metal enclosures of electrical appliances must be connected to a protective conductor. Water, gas pipes, strucutural metal parts of the buildings and ductings of airconditioning system must also be connected to the main equipotential bonding. COP06 – Isolation on fault. Protection using RCD, fuse, CB etc. must comply with Ra x Ia < 50V Ra = Resistance of earth electrode & protective conductor; Ia = operating current of protective device (sensitivy of RCD and 5s current trip for inverse time relay). 50V is the safe contact voltage defined by IEC60749-1.
COP07 –Earthing resistance must be less than 10Ω for operation of RCD but resistance of less than 1Ω is targeted.
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INSTALLATION – MS1979
COP08 – Electrical equipment must be mounted within materials that can withstand temperatures produced (by the equipment). COP10 – Water heaters or forced air heaters or steam generators must be equipped with over heating devices (i.e. use o/t cut-out etc.). COP12 – In > IB, COP13 – Iz > In COP14 – I2 < 1.45 x Iz In = nominal current of protective device; IB = design current; Iz = current capacity of cable ; I2 = tripping/effective operation current of protective device. COP16 – Requires determination of short circuit current within the installation. Effectively this requires every TNB district engineer to issue information on short circuit at the point of common coupling (PCC) at the locality of installation.
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INSTALLATION – MS1979
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COP10 to COP 14 IB –decide current rating of circuit IB > load current
(1) IB < In < Iz (2) I2 < 1.45 x Iz Select protective devices, In > IB
Check I2 < 1.45 Iz
Calculate cable size based on:
In
= nominal current rating of protective devices
Iz > In
I2 = current ensuring effective operation within time prescribed of protective device
Iz = current capacity of cable. Cables
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Protection devices
Calculate current from load
Electrical load 26th May 2011
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INSTALLATION – MS1979
COP19 – Surge Protection Device (SPD) is RECOMMENDED for supply from overhead lines. COP26 – Bending radius of 12 times diameter of cable is mandated. This effectively requires that elbows and junctions be used where cable changes direction.
In Malaysia, many wiring installation WILL FAIL THIS CRITERION. COP27 – Space factor for conduit shall be 40% and for trunking shall be 45%. COP28 – Cables installed behind walls (i.e. embedded in concrete) shall be horizontal or vertical parallel to the edges of the room and within 150mm from top and 150mm from edge of wall. In Malaysia, many wiring installation WILL FAIL THIS CRITERION as cables are commonly installed diagonally fully and in many cases partially (picture 1).
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9 INSTALLATION – MALAYSIAN STANDARDS
COP28 – Cables installed behind walls (i.e. embedded in concrete) shall be horizontal or vertical parallel to the edges of the room and within 150mm from top and 150mm from edge of wall.
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9 INSTALLATION – MALAYSIAN STANDARDS
COP30 – Wiring within ceiling space (under roof) must be provided with mechanical protection (i.e. installed within APPROVED conduit). In addition they must be installed either parallel or perpendicular to the edges of the wall. COP31 – Water heater circuits shall have 2-pole switch installed at suitable location. At the vicinity of the heater a socket outlet is required (unswitched is acceptable). COP32 – Air Conditioner circuits shall have socket outlet (unswitched type is accepable) at vinity of unit. COP35 – Size of neutral conductor must be same size as phase conductor. COP36 – Size of neutral conductor may be reduced (reference to COP35) at the discretion of the Professional Design Engineer (i.e. only a P.Eng can decide). COP39 – Minimum cable size shall be 1.5mm² copper or 2.5mm² aluminum. Therefore the practice of using 1.25mm² copper cables is illegal!
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9 INSTALLATION – MALAYSIAN STANDARDS
COP41 – Allowable voltage drop is 4%. Voltage drop for motor starting may be 10%. COP42 – Soldered connections to connect or terminate cables ARE NOT ALLOWED (see COP43 below). COP43 – Connections of 2 lengths of conductors shall be by sockets and crimping. COP44 – Cables for final sub circuit shall NOT BE JOINED. COP51 – RCD (or current type ELCB) for single phase installation shall not exceed 100mA (the previous quoted in the regulations was 30mA). COP52 – RCD for 3-phase installation shall not exceed 100mA. Three units of single pole type RCD instead of a 3-phase RCD may be used PROVIDED no 3phase load(s) is/are served. COP53 – Hand-held equipment shall have RCD not exceeding 30mA.
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9 INSTALLATION – MALAYSIAN STANDARDS
COP54 – RCD not exceeding 10mA shall be installed for special location (places of public entertainment; wet places; protection of electric water heaters). COP56 – Requires RCD to be regularly tested, at least twice a year. COP59 – It is recommended to place SPD before RCD (on the supply side), see figure 2.
COP61 – SPD should be rated not less than 5kA. COP64 – The minimum earth connection from SPD to main earth terminal shall be not less than 10mm² copper and shall be as short as possible (0.5m).
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9 INSTALLATION – MALAYSIAN STANDARDS
COP83 - Supervision of work on LV 3-phase installations shall be under direct responsibility of Wireman (3-phase restriction). The Wireman shall be required to certify completion under Form G. COP 84 – Testing for single phase installation shall be by Wireman (singlephase or 3-phase restriction) under Form H. COP 85 – Testing for 3-phase installation shall be by Wireman (3-phase restriction) under Form H. COP86 – Other installation at higher than low voltage shall be tested by a Electrical Services Engineer under Form H. COP87 – Electricity SHALL NOT BE CONNECTED until Forms G & H are submitted by the owner or building operator. COP88 – Insulation measurements shall be carried out on LV installation using dc voltages. Where 500Vdc is applied, the insulation resistance shall be more than 1MΩ. COP91 – Every completed installation shall have as-built electrical diagrams prominently displayed. Diagrams shall be endorsed by the professional design electrical engineer.
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26th May 2011
25 Common Problems for M&E Engineers Armada Hotel , Petaling Jaya 26th May 2011
5 Common Contract Management Problems
Ir. Looi Hip Peu |
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