--- title: "Electrical services principles, wiring, safety" subject: "Building Technology" chapter: 12 key: "semester_6/building_technology:electrical-principles-wiring-safety" source: https://www.bctengineer.com/q/semester_6/building_technology/electrical-principles-wiring-safety site: BCT Engineering --- # Electrical services principles, wiring, safety Building Technology · Chapter 12: Other services in building - Asked in: 2067 Asar (old course), 2+3+3 marks - Video: [14 BUILDING SERVICES ELECTRICAL SERVICES AND LAYOUT Diploma in Civil Engineering](https://www.youtube.com/watch?v=fN3ijOHz3AU) — SSP, SECTOR-22, GANDHINAGAR - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/building_technology/electrical-principles-wiring-safety - Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-12 ## Question What are the general principles of electrical services systems? Explain wiring systems and also discuss about the safety precautions to be adopted while using electricity and its appliances. ## Short answer General principles are safety, adequacy, economy, reliability, accessibility, and standards. Common wiring systems are cleat (temporary), batten, surface/concealed conduit (safest), and sheathed cable. Safety precautions include earthing metal parts, using MCB/ELCB, connecting switch in phase wire, avoiding overloading, and maintaining insulation with quality materials. ## Answer #### General principles of electrical services - **Safety:** protect people and property from shock and fire (earthing, fuses, MCB, RCD/ELCB). - **Adequacy:** the number of points, wire capacity and load capacity must be enough for present and future use. - **Economy and simple design:** short runs, balanced loads on the phases, minimum voltage drop (not more than 3-5%). - **Reliability and continuity:** separate circuits for lighting (5 A) and power (15 A); a fault on one circuit should not stop the others. - **Accessibility:** distribution board at an accessible central location; switches at about 1.2-1.4 m height. - **Standards:** follow the Nepal electricity rules and standards (NBC 207 / IS 732 / IEC); use ISI/NS-marked materials. - **Appearance and flexibility:** concealed wiring where possible; provision for extension; good lighting levels. #### Wiring systems ##### 1. Cleat wiring PVC or VIR cables held in porcelain/wooden cleats on the wall. Cheap and temporary; used on construction sites and at exhibitions. Poor appearance and not safe for permanent use. ##### 2. Casing-capping wiring Cables laid in the grooves of a wooden casing and covered by a capping. Cheap but old-fashioned; a fire risk and affected by moisture and termites; rarely used now. ##### 3. Batten wiring Sheathed cables (TRS/CTS or PVC-sheathed) are clipped onto teak wood battens fixed to the wall. It looks neat and is cheap, but is poor against moisture and fire; used in dry places. ##### 4. Conduit wiring Cables drawn inside PVC or GI pipes (conduits). - *Surface conduit:* fixed on the wall surface; easy to repair; used in workshops. - *Concealed conduit:* buried in the plaster or slab; best appearance, safe against fire, moisture and mechanical damage. Most used in modern buildings, but costly and difficult to alter. ##### 5. Sheathed (TRS/CTS) and lead-sheathed wiring Cables with a tough-rubber or cab-tyre sheath (TRS/CTS), or with a lead cover, clipped directly to the surface. Resists moisture; used in damp areas; lead-sheathed wiring is costly. ##### 6. Others Metal-sheathed cable, bus-duct/trunking (large buildings and industry), underground cable. **Comparison:** concealed conduit is the safest and neatest, cleat wiring is the cheapest (temporary work), batten is the cheapest permanent system, and conduit/trunking is used in most multistorey buildings. **Systems of distribution:** the *tree (branch) system* and the *ring/loop system* are the two layouts; the ring system gives better voltage and reliability. #### Safety precautions in using electricity and appliances - **Earthing:** connect all metal parts of appliances and the DB to earth (earth pit with a GI plate/pipe, resistance less than 5 ohm for buildings) to avoid shock. - **Protective devices:** fuses, MCB, MCCB and ELCB/RCD (30 mA) to cut the supply on overload, short circuit and leakage; a lightning arrester on the roof. - **Proper materials:** use standard-quality wires, switches and fittings of the correct current rating, and the proper conductor size for the load. - **Switch only the live (phase) wire:** switches and fuses on the phase; neutral kept solid; use 3-pin plugs. - **Insulation and joints:** all joints properly made and insulated; no bare wire; use junction boxes. - **Avoid overloading:** do not connect many appliances to one socket; use separate circuits for heavy loads (AC, geyser). - **Safe location:** keep wiring away from water pipes, gas lines and hot surfaces; place sockets and switches out of reach of children and away from bathrooms (or use waterproof types), at sufficient height. - **During work:** switch off the main supply before repair; use insulated tools, rubber gloves and mats, and "danger/men at work" notices; avoid working in wet conditions; employ qualified electricians only. - **Fire precautions:** keep extinguishers (CO2/dry powder) nearby; never use water on an electrical fire. - **Testing and maintenance:** test insulation resistance (megger) and earth continuity after installation and periodically. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What circuits are normally kept separate for reliability? A. Lighting (5 A) and power (15 A), with heavy loads like AC and geyser on their own circuits B. Lighting and fans on the same 15 A socket C. All loads on a single circuit D. Only the kitchen circuit Answer: A. Separate lighting (5 A), power (15 A) and heavy-load circuits mean one fault does not stop the others. (Key point: Circuit separation) 2. Which wiring system is safest and neatest for modern buildings but costly and hard to alter? A. Cleat wiring B. Batten wiring C. Casing-capping wiring D. Concealed conduit wiring Answer: D. Concealed conduit is buried in plaster or slab, safe against fire, moisture and damage, but costly and hard to modify. (Key point: Conduit wiring) 3. What is cleat wiring used for? A. Permanent wiring in multistorey buildings B. Temporary work such as construction sites and exhibitions C. Underground wiring D. Damp areas needing waterproofing Answer: B. Cleat wiring is cheap, poor in appearance and unsafe, so it is used for temporary work. (Key point: Cleat wiring) 4. What is the purpose of earthing metal parts of appliances and the DB? A. To increase current flow in the load B. To avoid shock by providing a path to earth (earth resistance below about 5 ohm) C. To reduce the wire size D. To switch off the neutral Answer: B. Earthing gives leakage current a safe path to earth so people are not shocked. (Key point: Earthing) 5. On which conductor should switches and fuses be placed? A. The neutral wire B. The earth wire C. Both neutral and earth D. The phase (live) wire, with neutral solid Answer: D. Switching the phase makes the appliance dead when off; the neutral is kept solid (unswitched). (Key point: Switch on phase) ## Related in Building Technology - [Short note: General principles of electrical services](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aelectrical-services-principles-short) — Building Technology, chapter 12 - [Safety precautions in electrical works](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aelectrical-safety) — Building Technology, chapter 12, asked 3× - [Electrical wiring systems](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aelectrical-wiring-systems) — Building Technology, chapter 12, asked 3× - [Fundamental requirements of electrical wiring](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aelectrical-wiring-requirements) — Building Technology, chapter 12 ## Related in other subjects - [General electrical rules for installation and wiring](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Aelectrical-rules-installation) — Industrial Power Distribution and Illumination, chapter 1, asked 3× - [Precautions while applying cement mortar](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Aprecautions-applying-cement-mortar) — Civil Engineering Materials, chapter 6, asked 3× - [General safety rules in a machine workshop](https://www.bctengineer.com/question.md?key=semester_2%2Fworkshop_technology%3Aworkshop-safety-rules) — Workshop Technology, chapter 1 - [Cost of electrical energy for appliances](https://www.bctengineer.com/question.md?key=semester_1%2Fbasic_electrical_engineering%3Aelectricity-cost-toaster-bulbs-dryer) — Basic Electrical Engineering, chapter 1