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Top Electrical Design - Questions and Answers

Top Electrical Design - Questions and Answers 

Prepared By: Mahmoud Essam Hezzah
Electrical Design Engineer
كتاب شامل ومتكامل فى التصميم الكهربى يتناول تصميم جميع الأعمال الكهربائية بالمشاريع من توزيع كهربي وتأريض وتيار خفيف ومحركات كهربائية
Top Electrical Design - Questions and Answers

Table of Contents
1. Have you previously done design for electrical work?
2. Have you previously done shop drawing (execution) for electrical (high current) work?
3. Are you familiar and have used the following computer software’s: 
4. What are the de-rating factors considered in cable installation?
5. How can you overcome the problems of voltage drop? 
6. What are the precautions to be taken in mind when selecting an emergency feeder running         next to another feeder fed from normal supply? 
7. What is the national color code of a three phase circuit?
8. What is the meaning and the difference between (AF) & (AT) of C.B? 
9. What are the types of contracts? State the difference among them?
10. What is difference between tender drawings, design drawings, shop drawing (Execution) &        as built drawings?
11. What are the types of tests required for electrical equipment? What are the differences?
12. What are the types of circuit breakers? State some applications for each?
13. What is the difference between thermal setting & magnetic setting of C.B? 
14. How can you improve the selection of a system earthing arrangement? 
15. What is the meant by TVSS or SPD? 
16. What are the types of Discrimination (Selectivity)? State the difference? 
17. What is Cascading? 
18. Estimate the demand load (VA/m2) regarding lighting, sockets, A/C, Equipments...etc for the following type of buildings: Hotels; Residential; Commercial/Offices; Health
Care/Hospitals; Educational/Schools 
19. What is meant by: IP54; NEMA 
20. What are codes & standards can be followed in lighting design?
21. What are the types of earthing systems according to IEC? Explain each & where           recommended to be used? Compare among earthing systems
22. Calculate the grounding conductor size & the grounding resistance according to BS 7430:1998 of grid of length 80m width 40m, 12 rods with separation distance of 20m where rod length is 3m, rod diameter is 20mm, soil resistivity is 450 Ω.m, grounding conductor laid 0.8m below ground. 10 earth lattices (600mm x 600mmm) are bonded to the earth loop. Suppose that the symmetrical fault current is 20KA in 1sec duration. Where the grounding conductor is chosen to be copper conductor and the initial temperature of conductor is 30°C & final temperature is °250C. After calculation find out if the grid safe or not safe? 
23. What is the Dynamic UPS (No Break Generator)? State some applications? Compare with Static UPS
24. What are the types of cable trays? State some applications? How can you size a cable tray? What is the difference between cable tray & cable ladder & which is less expensive? State applications for cable ladders? 
25. State some applications for using isolating transformers? What is the advantage of using it? 
26. What are the common types of conduits? State some applications? How can you size a conduit? 
27. What characteristics does a luminaire need to be a good one?
28. What are the SEC standard specifications for LV distribution panels sizes for transformers 500 kVA, 1000 kVA, 1500 kVA from where:
o Incoming CB. Rating
o Incoming Cables for standalone LV panel
29. What is RGB LED?
31. What are the different types of Lighting System Controls?
32. What is the difference between IP, NEMA, IK, IC & IM
33. What is the difference between horizontal, vertical illumination & general, task lighting? How can you make calculations for each? State some examples for each?
34. What is color rendering? State the color renderings for sodium lamps, metal halide lamps, fluorescent lamps & halogen lamps?
35. What is illuminance? State the recommended illumination level for Office, Surgery operating room, Bed room, Class room, Sitting & Corridors
36. What is Color Temperature? State some of them
37. What is the difference between Fluorescent lamps type T2, T5, T8 & T12? 
38. Can we make interconnection bonding among these systems: 
o Grounding System
o Lightning Protection
o Low current & Communication Grounding System
39. Give some types of different lamps showing: type, manufacturers, wattage, lumen output, peak intensity, colour temperature, lamp holder (cap), life time and dimensions?
40. What are the recommended IP and IK code specifications for distribution boards? 
41. Calculate the number of luminaries required for office (5x6m), height = 3m, consider type fluorescent lighting fixture each have lamps 2x36W. Luminous flux of each lamp 3200 lm, utilization factor is 0.48 and maintenance factor is 0.75. Notice that the required maintained illumination level is 500 lux
42. What is the recommended LV system voltage? Give some examples for the system voltages & frquencies in different countries?
43. What is LEED & how can you improve your design to match the LEED requirements? 
44. Which one could achieve more lumen output prismatic or opal diffusers considering same lamps? Why? State application
45. What are the different types of substations?
46. Insulation systems are rated by standard NEMA classifications according to maximum allowable operating temperatures. Explain
47. Differentiate between: 
o Directional & diffuse lighting.
o Symmetric & asymmetric lighting.
o Direct, indirect lighting & Direct-indirect lighting.
48. In case of presence of 2 sockets back to back in two different rooms. Can we put them directly back to back or we should leave a distance between them? 
49. What is the difference between demand factor & diversity factor?
50. What are the different methods of starting motors? State the difference among them? State Applications?
51. If we have a big room & contain many sockets which will need about 5 branch circuits. Can we feed these circuits from different phases? Why?
52. How can you earn LEED certifications for new constructions? What are the LEED ratings? .
53. If you have a refrigerator or A/C or any other motor equipment that works on 50Hz, can you make it work on 60Hz Power Supply?nnected load for each villa (dwelling unit) is 60 KVA. Estimate the number of pillars, transformers & distributors required for this project. Considering that only 400A pillars & 1000KVA Transformers ratings are available. System Voltage is 13..8KV/380-220V. Draw schematic single line diagram to what you obtained. 
55. What are the IEC Switchboard Forms for Internal Configuration? State the difference?
56. What is distance between down conductors in lightning system design? How can you design the mesh?
o For building less than 15M height
o For building 80M height.
57. Give a small brief summary for each of these types of lamps 
o Incandescent
o Halogen
o Fluorescent
o Compact Fluorescent Lamps
o LED (Light Emitting Diodes)
o High-Intensity Discharge Lamps
o Low-Pressure Sodium Lamps
58. What is DALI? 
59. Estimate the circuit breaker, disconnecting switch and cable size for:
o Lighting load 3000VA single phase. Feeder wire length is 40 m.
o Outdoor A/C load 3000VA single phase. Feeder wire length is 40 m.
o Panel Board with three single phase loads(3000VA, 4000VA, 2000VA).Feeder cable length is 200 m.
o Where; the system voltage is 380/220V; suppose that total cable de-rating factors is 0.8; suppose cable routing in pipes.
o Use the following cable catalogue cuts for sizing cables.
60. When we should use a remote radiator for a diesel engine generator? 
61. Calculate capacitor rating required to improve the power factor of a motor P=500KW from P.F1= 0.8 to P.F2= 0.9?
62. What is EIB? 
63. Calculate the three phase short circuit current at secondary side of a 1 MVA transformer 13.8KV - 480/227V, 60 Hz; impedance is 6 percent and assuming sustained primary voltage during fault? 
64. What are the basic factors would you take into consideration while making lighting design?
65. Calculate the voltage drop of cable with load 32KW - three phase, cu cable C.S.A= 16mm2, Ra.c= 1.38 ohm/km, X= 0.1068 ohm/km, CosØ = 0.8, cable length =120m, system voltage is 380/220V. 
66. What does GFCI & AFCI stands for? What is the difference? State some applications?
67. What are LPD specified in ANSI/ASHRAE/IESNA Standard 90.1? Can you state the methods used for computing LPD & give some examples? Does the LPD values specified in ASHRAE accepted by LEED? 
68. What is power factor? What are the equipments that create poor power factor? How can you improve power factor of your system? 
69. Choose the correct answers if any. What is the purpose of discrimination?
o To ensure continuity of service
o To only trip the device just above the faulty feeder
o To increase servicing time for trouble-shooting
o To increase productivity
70. Compare between magnetic ballast & electronic ballast. 
71. What are the trade sizes of conduits? 
72. In an installation, circuit breaker CB1 is placed upstream from circuit breaker CB2. A short-circuit current occurs downstream from CB2. CB2 opens and CB1 stays closed. This is a case of: 
73. For each of the faults A, B, C in the diagram, say whether or not the protection device opens: 
74. The fault current downstream from circuit breaker CB5 is 400 A. With total discrimination, which circuit breakers will open?
75. State which statement is true and which is false: Standard IEC 60364: Section-3-32 & 4-48 on premises with a risk of fire 
o Imposes use of a 500mA RCD device.
o Recommends use of a TT or IT system for the electrical installation on such premises.
o Prohibits use of a TN-C system.
o In TT, IT and TN-S systems, a 300mA RCD eliminates the risk of fire.
76. What are The Main Functions of Earthing/Grounding Systems? 
77. What is the difference between (Ics) & (Icu) of C.B? Which one is considered in design? 
78. State the functions of circuit breaker
79. What is more danger on the human body AC current or DC current & why? What is the effect of AC current on the human body? 
80. In order to select the right circuit breaker. What are the Criteria’s of choice that should be followed? .
81. Compare between earthing systems from the point of: 
o Protection of people.
o Protection against fire.
o Ease of implementation
o Continuity of service
o Upgradable installation.
o Cost saving
82. What are the Benefits of improving Power Factor?
83. How the penalty on power factor is calculated? 
84. What are the different types of armoured cables which are more expensive, which one can withstand more mechanical load, is the 2 types are accepted by BS & IEC? 
85. State the Cable Insulation Temperature Limits (Continuous Operating Temperature, Emergency Temperature & Short Circuit Temperature) for XLPE & PVC 
86. What does mean by day lighting? 
87. Transformers are classified into various categories, according to their: Use, Cooling method, Insulating medium. State & explain each classification. Which is better & why? 
88. What are the important factors required for selecting a suitable cable to transport electrical energy from the power station to the consumer? .....................95
89. What is the difference between Rapid-Start and Instant-Start of fluorescent lamp? 
90. What is tap changer? 
91. What is the difference between beam angle & cut-off angle of a luminaire? What are the different beam classifications & State the difference between them?
92. What are the levels of protection (Coordination of protective devices) for the motor starter? 
93. Calculate maintained illumination level for clinic (4x6m) - height = 3m, consider 4 fluorescent lighting fixture each have lamps 4x36W. Luminous flux of each lamp 3000 lm, utilization factor is 0.50 and maintenance factor is 0.70. 
94. What is difference between low smoke halogen free cables & fire resistant cables & fire alarm cables?
95. What is the distance between sockets that should be followed in design?
96. Wrong positioning of desks relative to luminaries could cause reflected glare. 
o Define glare.
o Which position of luminaire is right to avoid glare?
97. When many cables are laid on cable tray, what are the factors that determine the final ampacity of each cable?
98. What is the difference between Normal load, Emergency load & Critical load? State an example for each.
99. State the Types of static UPS 
100. If the power factor of a certain electrical installation is low how can the power factor to be improved / corrected? .
101. What are the devices to be used for earth leakage protection / ground fault protection?
102. What is Voltage Drop? What are the factors that determine the Voltage drop of a cable/wire? Write down the V.D equation for single phase cable & 2 phase for 3 phase cable 
103. What are the C.T. & P.T? When do we use each one and why?
104. What does these abbreviations stands for: PVC, XLPE & LSF?
105. Define the Grouping Factor? When does it considered in cable size calculations? Is it applicable for multi core or single core cables?
106. A branch panel board with total connected load 25 KW & P.F. = 0.8. Calculate Main Feeder Cable and Main C.B? 
107. Mention the different types of conduits used in electrical systems routing inside high rise buildings? What is the common usage for each?
108. Mention the different types of conduits used in electrical systems routing inside high rise buildings? What is the common usage for each? 
109. What is the difference between, molded Case Circuit Breaker and miniature circuit breakers? 
110. Suppose you are buying a transformer. You have two options: TR1is 11/0.4KV & Z = 4 %, TR2: is 11/0.4KV & Z = 6 %. Which one you choose & why? Taking into consideration, you need 380V on the secondary at full load
111. Compare between the following types of lamps according to their Power Range, Efficacy, Lumens, Life Time, Color Temp and CRI.
o Incandescent and Halogen
o Fluorescent
o Compact Fluorescent (CFL)
o Mercury Vapor
o Metal Halide
o High Pressure Sodium (HPS)
o Low Pressure Sodium (LPS)
112. There are new specifications created by SASO to prohibit entry of any plugs or sockets not conforming to the specifications and this should be effective on (23/02/2010). What are these specifications & what are the types specified for 127V Plugs/Sockets & 220V Plugs/Sockets? 
113. What is meant by UL Listed product?
114. Does the voltage supply fluctuation affects the lamps? How? 
115. What is the ballast? State its function & types of ballasts. 
116. What is the difference between a kW and a kWh? What is measured by electric utility? 
117. What are the different types of conductors according to NEC code? 
118. How can you estimate the electrical consumption per month for residential buildings? 
119. What is star-delta starting? Why is it used? What are the advantages & disadvantages of using this method? Should we immediately install soft starters on all our existing motors?.
120. How the Electricity Bill is computed?
121. What are the different standards of sockets? Draw them & state the difference?.
122. What are the international codes, standards, regulations & specifications? State some of them that can be followed in electrical design? 
123. What are the different types of local power cables for low & medium voltages? 
124. When can we use neutral with C.S.A equal to the C.S.A of the phase & when can we use reduced neutral and with C.S.A less than the C.S.A of the phase? How can we choose the reduced neutral in 3 phase-systems 
125. What are the types of emergency lighting? State the difference? How batteries shall be provided?
126. State the target areas for Emergency Lighting to be provided?
127. What are lighting levels & uniformity mentioned in standards for emergency lighting? 
128. What are the different systems used in central battery system? Compare between them. 
. What are the advantages of using Self Contained EM Lighting? 
130. What are the advantages of using Central Battery System? 
131. How can you calculate the current carrying capacity or the size of busbar? 
132. Why you use sine wave for ac power supply why not triangle wave or square wave?
133. Do we can put two branch circuits in one conduit?
134. Why do 50 Hz transformers cost more than 60 Hz transformers? Does 50 Hz transformer could work on 60 Hz transformers & How? 
135. How can you calculate the full load current for different sizes of motors (1-ph, 2-ph & 3-ph)?
136. State the way of calculating the short circuit at any point within a LV installation according to IEC & Egyptian Code for electrical installation
o Illuminance is measured in footcandles (lumens/square foot) or lux (lumens/square meter). Where one footcandle equals -------- lux.
o Luminous intensity is measured in Candela or Lumen (Lu).where one Candela equals -------- Lumen (Lu).
138. Compare between using Central Battery System and Self Contained EM Lighting
139. What is the difference between circular & sectoral sections in cables?
140. How can you size the earthing conductor according to size of phase cable size or according to C.B. size using NEC & IEC?
141. Why CU wires are preferable in indoor distribution while Al cables are preferred in electrical transmission? 
142. For the following factors. Explain the effect of increasing or decreasing these factors on short circui
o Cable length
o Cable CSA
o Conductor Type
o Transformer per unit impedance
o Transformer load.
o System Voltage
o Bus Bars
o Circuit Breakers
143. What are the different types of cables? 
144. What are the standards C.S.A’s for power cables for low, medium & high voltage?
145. What is the difference between armoured & unarmoured cables? 
146. Screening of MV cables is used in earthing. Right or wrong? 
147. How can you convert American Wire Gauge (AWG) to square mm cross sectional area?
148. What is the problem of unloading the transformer? 
149. For replacing an existing Lighting system of fluorescent lamps 110 Volt, 60 Hz by new fluorescent lamps 220 Volt, 60 Hz, which of the following devices should be changed Lamp, Ballast and Starter?
150. How can you convert from NEMA to IEC Enclosure? 
151. What are the different risks on human that caused by electricity? Explain. 
152. What are the different tripping characteristics and rated currents for MCB’s? 
153. What is the obstruction lighting? What are their types? How it’s designed?
154. What specifications must be applied in cable insulation?
155. Determine how many 6mm2 cu single stranded conductors are permitted in a trade size 1¼ rigid metal conduit (RMC)?
156. Does the way of mounting, positioning and orientation of a lamp (Burning Position) affect the burning?
157. According to NEC. Determine the minimum size rigid metal conduit (RMC) allowed for the 9 mixed conductor sizes and types described as followed:.143
o 3 single stranded wires cu of 4mm2 each
o 3 single stranded wires cu of 10mm2 each
o 3 single stranded wires al of 16mm2 each
158. What are the most available sizes for LV HRC fuses? 
159. A 200-ampere feeder is routed in various wiring methods (EMT) conduit & (RMC) conduit from the main switchboard in one building to a distribution panel board in another building. The circuit consists of muli-core cable 4x70 + 25 mm2 CU - XLPE/PVC unarmoured. Select the proper trade size for the various types of conduit and tubing to be used for the feeder. 
160. What are the capacities of PVC conduits for different cable sizes (single & multi-core)? 
161. What is the relation between C.B & Busbar? 
162. How can you find the cable size with regards to C.B Size? 
163. What are the most available sizes for disconnecting switches?
164. What are the C.B. ratings & short circuit capacities in American & European standard?
165. What is the control gear of a luminaire?
166. What are the methods of cooling of transformers? What does ONAN refers to?
167. What is the accepted percentage of loading a transformer? Can we increase the percentage of loading the transformer more than 100%? Explain.
168. State the advantages of using dry type transformers over oil immersed type? 
169. What is the information necessary while selecting the transformer protection system?
170. What are the advantages of selecting outdoor distribution transformers kiosks? 
171. What are the requirements for fire water pump electrical connection as per NFPA 70? 
172. When shall we use circuit breaker + back-up fuse as switchgear combinations?
173. What are the sizing recommendations for fire pump applications including (sizing the generator set, sizing the utility circuit breaker or fuses, sizing the feeder conductors, sizing the automatic transfer switch, sizing the generator circuit breaker) as per NFPA 70?
174. What are the main parts of transformer compartment (Kiosk)? 
175. Using given legend. Draw the wiring diagram for: 
o 1 Way - 1 Gang Switch.
o 1 Way - 2 Gang Switch.
o 2 Way (3 Way) - 1 Gang Switch.
o 2 Way (3 Way) - 2 Gang Switch.
o Intermediate (4 Way) - 1 Gang Switch.
176. Discuss the construction for LV & MV power cables? 
177. What are the different distribution losses in industrial facilities?
178. What are the types of insulations that can be used for cables? 
179. What are the main functions of luminaire?
180. How can you calculate the reactive power Capacitor Bank (power factor correction)? How can you choose the capacitor bank according reactive power from standard? How can you calculate the circuit breaker of capacitor bank? What are the available LV Standad Automatic Capacitor Banks?
181. What is the difference between AWA and SWA?
182. How can you classify lighting according to applications?
183. State some demand factors for different loads that are being used in American NEC Standards? 
184. What are the different classifications of luminaries? Give brief discussion for each. 
185. State the difference in wiring between: 
o 2-Way Switch & 3-Way Switch.
o 4-Way Switch & Intermediate Switch.
186. What is the ATS & what are the main different parts of ATS? 
187. Specify different ratings of ATS?
188. What are the advantages of using Busbar Trunking System (Bus Duct)? 
189. What are the different types of ATS Devices? 
190. When should we use Busbar Trunking (Bus Duct) System? 
191. What is the acceptable percentage voltage drop that can be reached in L.V. calculations?
192. State the application & operation of the contactor and circuit breaker based transfer switches (ATS)?
193. State the application & operation of the solid state transfer switches (ATS)?
194. When should we use tap-off boxes Busbar Trunking (Bus Duct) System? 
195. What is the minimum requirement for transfer switch (ATS) arrangement that should be followed for essential & critical loads of health care facilities? 179
196. What are the applications of using Busbar Trunking (Bus Duct) System?
197. What is Busbar Trunking (Bus Duct) System?
198. What are the relations among transformers, main C.B’s and Bus Duct Ratings assuming that the system voltage is 380/220V? 
199. What are the different available standard ratings for Bus Duct? 
200. Which is better in power distribution AC system or DC system? Why? 
201. Which is the Cable Bus? What are the applications of using it? What are the advantages & disadvantages of using it? What are the type of conductors & configurations used? Compare between ampacities using Cable Bus & other normal cables
202. What are the different batteries types - technologies? State the difference?.
203. Consider a pillar with a 3 phase load 200A. The cable length feeding the pillar from a transformer is 140 meters. This cable is laid directly in ground and is grouped with another 5 cables in the same trench. Which size of cable below you prefer to use in order not to exceed 2% voltage drop, p.f = 0.8 & why? 
204. What are the expected room sizes (dimensions) for standby generators with these sizes: 80, 100, 125, 175, 200, 350, 400, 500, 600, 750, 900, 1000, 1500KW
205. State some diversity factors of different purposes (ex: lighting, sockets, air conditioning …. etc) for different type of premises (ex: residential, offices, hotels... etc) according to Egyptian Code?
206. Can you estimate the demand load of a building using its type & its gross area according to Egyptian Code? 
207. Compare between LV & MV generators
208. Calculate the grounding conductor size & the grounding resistance according to IEEE Std 80-2000 of grid of length 80m width 40m, 12 rods with separation distance of 20m, rod length is 3m, rod diameter is 20mm, soil resistivity is 450 Ω.m, grounding conductor laid 0.8m below ground. Suppose that expected fault symmetrical current is 20KA in 1sec duration. Where the grounding conductor is chosen to be 40% conductivity copper-clad steel conductor 
209. What are the IP references preferred for switchboard assemblies? 
210. What are the main aims of tunnel lighting? What is necessary to know about tunnel lighting? When to light tunnel by day? When to light tunnel by night? How to light tunnel by day? What are the 5 zones of tunnel lighting? Which type of lamps to use? What are the types of tunnel lighting systems? What is the short tunnel & underpass? How to illuminate tunnels for different lengths in day time 25m, 75m and 125m? What are the tunnel lighting arrangements and state advantages & disadvantages of each? 
211. Select the required automatic capacitor bank for a transformer rating: 1600 kVA, Voltage: 13.8/0.38 kV, Connected Load: 1516 kVA = 1289 KW, Assumed PF/ Target PF: 0.85 / 0.95? What are the minimum & maximum harmonic orders for this capacitor bank? 
212. What is harmonics? What is the problem of harmonics? What is k- factor? How to calculate K-Factor? What is K-Factor of a transformer? Why we calculate K-Factor of a transformer? What are the advantages of calculating the K-Factor of a transformer? What are the disadvantages of using the derated standard transformers instead of K-Factor? What should be remembered when using a K-Factor Transformer? How K-Factor Transformer could be calculated?
213. Consider transformer 1600 KVA feeding an office building with total lighting load 201 KVA, total power load 483 KVA, total HVAC load (AHU’S) 386 KVA and total EWH load 54 KVA. Select the k-factor required for this transformer. 
214. What is difference between prime generator & standby generator? 
215. What is difference between metal-enclosed switchgear & metal-clad switchgear?
216. What do you know about metal-enclosed switchgear, metal-clad switchgear and arc resistant switch gear? 
217. Compare between Static Transfer Switches (STS) and Automatic Transfer Switches (ATS)
218. State the difference between the three types of ballasts Magnetic, Rapid start, HF ballasts. What is the recommended ballast for T12, T8, T5 & CFL? 
219. Can we dim LED Light? How? Is there any flickering while dimming? Are there any Changes in color and efficacy with dimming?
220. According to SEC Distribution Materials Specification. What are the available ratings for transformers Pole mounted & Pad mounted? What are the maximum accepted losses? What are the available tap changer settings? What is the recommended vector group, Impedance Voltage, Temperature Rise, Noise Level, Short Circuit Level, Degree of Protection, Dimensions, LV bushings/terminals?
221. What’s the reason of grounding or earthing of equipment?
222. What is difference between power transformers & distribution transformers? 
223. What will happen if DC supply connected to 100W bulb?
224. Can an armoured cable be laid in a PVC conduit for aesthetic purposes?
225. Is it permissible to install PVC/SWA/PVC cable in Zones I and II flammable areas? If so, what is the authoritative document?
226. Is it permissible to use aluminum twin & earth cables? 
227. What are the codes of armoured cable glands? What is application for B/W & C/W?
228. What are the minimum CSAs for process instrument cables, power cables & control cables? 
229. Is it possible to use armour of a power cable as its earthing conductor? As an example - for 4 x 240mm cable, is it necessary to install separate earthing cable? Or is the armour of the cable enough for earthing? What is required by BS standards? 
230. What is the filling percentage that should be followed for trunking & conduits & cable trays as per British Standard? 
231. In order to reduce the size of the sub-main cable, we have installed a separate circuit protective conductor (CPC) with calculations satisfying this. Terminations have been completed as standard. However, on installation, the contractor has installed the CPC so it is not clipped to the armoured cable as normal practice, and takes a different route. Is there a standard that requires an armoured cable's CPC to be clipped to the cable? Is there an issue with running earths in a separate route to the armoured cabling, i.e. different lengths etc?
232. We have to pull a 3 X 70mm SWA cable through 80m of 100mm ducting. There will be a bend at each end up to the electrical switch room. The cable run between is more or less straight. Can you tell me what a reasonable bend radius would be to allow satisfactory pulling of the cable?
233. What power cables are suitable for direct burial in ground which may be prone to water logging? 
234. Calculate the annual savings and payback for installing an occupancy sensors given that: No. of fixtures = 20 x 2 Lamps; Fixture wattage Draw = 88 watt/Fix; Time length needed = 20 min/hr.; Operating hours = 4000 hrs./year; Electricity cost = 0.15 LE/kWh; Sensors cost = 200 LE 
235. For replacing an existing Lighting system of Incandescent lamps by a new fluorescent lamps, calculate the annual savings and payback given that: Existing lighting system.100 Lamps (200 watt/lamp); 200 watt lamp efficacy 17.5 Lm/watt; Fluorescent lamps 36 watt (44 watt incl. Ballast); Fl. lamps efficacy 70 lm/watt; Fl. lamps cost = LE. 15 (incl. Fixture); Annual operating hours 4000 hrs./year; Electricity cost = 0.15 LE./kWh
236. A 23,000 square meter high bay facility is presently lit with 800 twin 400 watt mercury vapour fixtures (455 watts per lamp including ballast.) What are the annual savings of replacing the existing lighting system with 800 single 400 watt high pressure sodium fixtures, (465 watts per lamp including ballast) Assume 8000 hours per year, an energy cost of $0.05 per kWh, and a demand cost of $6.00 per kW-month
237. Choose the correct answer:
o The efficacy of a light source refers to the Color rendering index of the lamp. A) True B) False
o Increasing the coefficient of utilization of the room cavity will in many instances increase the number of lamps required. A) True B) False
238 مبنى يحتوى على عدة وحدات سكنية يشتمل على الأحمال التالية: 
تحديد الحمل الأقصى لهذا المبنى مع السماح باستخدام معاملات التباين فى حالة:
(أ) إذا كان المبنى عمارة سكنية.
(ب) إذا كان المبنى سوق تجارى.
239 مبنى سكنى مساحته 350 متر مربع فى منطقة متوسطة اقتصادية ويتكون من ستة طوابق .المطلوب: حساب الحمل الأقصى لهذا المبنى طبقاً للكود المصرى.
240 إلى كم تنقسم مصاعد الركاب؟. 
 241 فيلا (وحدة سكنية خاصة) مطلوب تحديد الحمل الكهربائى لها طبقاً للكود المصرى ، وهى تحتوى على الآتى:
242 ما هى الأحمال التقديرية للأجهزة الكهربية المنزلية شائعة الاستعمال مثل: محمر الخبز؛ المكواة؛ الفرن الكهربي؛ مجفف الشعر؛ الثلاجة؛ جهاز الراديو؛ جهاز التلفزيون؛ مكنسة الكهرباء؛ دفاية الحجرة؛ .
غسالة كهربائية؛ غسالة كهربائية بالسخان؛ مجفف الغسيل؛ غلاية مياه؛ بروجيكتور؛ طابعة ؛ حاسب ألى؛ سخانات الحمام 
243 محول سعته الاسمية 1250 ك.ف.أ، و الحمل المعتاد لهذا المحول هو 750 ك.ف.أ، فما هو أقصى تحميل زائد مسموح به لمدة أربعة ساعات، و ذلك في درجة حرارة 30 ° مئوية؟
 يتم تحميله بحمل قيمته 450 ك.ف.أ لمدة أربع ساعات، وحمل قيمته 250 ك.ف.أ لمدة العشرين ساعة الباقية ONAN 244 المطلوب تحديد سعة محول توزيع بنظام تبريد .
245 مبنى سكنى تجارى على مساحة 600 م 2 عبارة عن: 
246 مما تتكون مصاعد الركاب؟ 
247 كيف يعمل المصعد الذي يعمل هيدروليكيا ؟ 
248 ما هى انواع الجر المختلفة فى المصاعد التي تعمل بمحرك كهربائي ؟ 
249 كيف يعمل المصعد الذي يعمل بمحرك كهربائي ؟ 
250 كيف يتم تحديد القدرة المطلوبة للمصاعد؟ 
251 كيف يتم حساب معامل الطلب للمجموعة إذا زاد عدد الكبائن فى المجموعة داخل المبنى؟ 
مكونة من ( 5) كبائن حمولة كل منها 1750 كجم وتتحرك بسرعة 3 م/ث، احسب الآتى:
252 فى مجموعة مصاعد منفذة بأسلوب التعليق بنسبة 1 .
253 كيف تعمل السلالم المتحركة؟ 
254 كيف يتم حساب الحمل الكهربى للسلالم المتحركة؟ 
255 ما هى الأحتياطات الواجب مراعتها عند التصميم لتغذية عدة سلالم متحركة داخل مبنى واحد؟ 
256 ما هى قدرات السخانات المستخدمة فى وحدات تدفئة المنازل من النوع الحائطى؟ 
و كيف يتم تحديد القدرة الكهربية لها؟ ؟(Moving walks and ramps) 257 كيف تعمل الحصائر والمنحدرات المتحركة .
258 ما هى أنواع و أنظمة التكيف المستخدمة ؟ و ما هى القدرات الكهربية لكل منها؟ 
259 ما هى القدرة اللازمة لأجهزة التكييف لكل من هذه الأماكن: المكاتب الكبيرة؛ ؛ المكاتب الصغيرة؛ غرف تدريس؛ مخازن تجارية؛ غرف مرضى في ؛ المستشفيات؛ غرف الفنادق؛ البنوك؛ الورش . والمصانع؛ المساجد؛ المحلات التجارية؛ سوبر ماركت؛ غرف كمبيوتر؛ مطاعم 
260 كيف تعمل طلمبات الحريق فى المبانى ؟ .
261 هل يجب استخدام طلمبة كهربائية وأخرى تدار بماكينة ديزل فى المبانى ؟ 
262 كيف يتم قدرة محرك طلمبة رفع المياه أو طلمبة الصرف الصحى أو طلمبة الحريق فى المبانى ؟ 
263 كيف تعمل سخانات حمامات السباحة ؟ 
264 كيف يتم حساب الحمل الكهربى للسخانات المستخدمة فى تسخين المياه فى المنازل الصغيرة ؟ 
265 كيف تعمل طلمبات رفع المياه فى المبانى ؟ 
266 كيف تعمل طلمبات الصرف الصحى فى المبانى ؟ 
267 ما هو التأريض؟ كيف يتم تحديد مخططات التأريض؟ اشرح انواع مخططات التأريض المختلفة؟ ما هو الأختيار الأمثل لمخططات التأريض؟ ما هو نوع التأريض الذى يفرضه النظام فى المملكة العربية السعودية؟ 
268 اذكر بعض الأحمال الكهربائية و الأسلاك و القواطع المناسبة لها حسب قدرتها و طرق تغذيتها؟ 
400 فولت موضحا رموز الأسلاك المستخدمة فى شبكة 3 فاز / 269 ارسم رسم توضيحى لتوصيل الأسلاك من العداد الى لوحة 3 فاز. ثم ارسم كيفية توصيل الأحمال الخفيفة و الكبيرة على الجهد الدولى 230 .
ثم ارسم رسم توضيحى لشكل المقبس المطابق و كيفية توصيله بالقطب أحادى الطور 230 فولت مع محايد. 
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