In the modern civilization, houses without television, computer, radio or refrigerator are the exceptions. It is nonetheless true that the average consumer has at best; a very sketchy idea of what he is paying for each time his electricity bill falls due.
For a civil engineer, in building construction it is very important to have fundamental knowledge of electrical work involved.
Electricity plays a vital role in all the services provided to a house but it is also very dangerous if not handled properly. Therefore all the electrical works should be carried out under the guidance of competent electrical consultant.
Following are the duties and responsibilities of an electrical consultant.
Depending upon the nature of use of the electricity, the electricity companies levy different tariffs. The temporary connections given for a project during construction are charged at higher tariff rates.
The temporary electricity connection (construction meter) is obtained from the authority. The necessary documents and procedure is described later on.
Before commencing a project, availability of electricity at the site is a basic requirement. Therefore considering the minimum load of construction machineries supply of electricity shall be made available from proper authority
For every new electrical connection, electricity board has laid down certain norms and procedures. Depending upon the nature of use, various categories have been made by the electricity board. Initially, starting with new construction on vacant plot, following procedure is adopted.
Subdivision office gives details of available load and rough estimate of transformer capacity. Division office will make necessary changes as per the rules of electricity board and prevailing site situations.
The division office further informs the zonal office about the demand of the load. Zonal office estimates the total expenditure for the desired load. The developer has to pay 15 % amount of the estimate as the supervision charge to the electricity board. The C.E then issues the sanction letter for the total load. After paying 15% supervision charges to electricity board; Developer will approach construction division of the electricity board with sanction letter & receipt of supervision charges.
Then construction division officers visit the site and order licensed contractor to start the work as per the estimates and specification of load sanctioned letter. Builder/ contractor will procure the transformer, H.T. cables, L.T. cables, main feeder pillars, sub feeder pillars, lugs, hardware etc.
All civil work construction of transformer room trenches inside the room, location of transformer, earthing pits, O.S.F, feeder pillars etc will be completed as per the contract and electricity board’s instruction.
Project engineer should check all electrical equipment and material as per specifications.
After completion of all electrical and civil work, the transformer is ready for charging. Construction division will issue a call letter to electrical inspector (P.W.D.). He will inspect the site for the following compliances
The electrical inspector issues the permission letter for charging the transformer / generator to construction division of electricity board, after confirming all above norms.
The executive engineer of the construction division issues the instruction to charge the transformer. Then the transformer is charged.
For getting the individual unit connections, the subdivision office prepares the quotations of the cost. After paying this quotation cost, the individual connections are sanctioned. Individual meters shall be fixed with proper earthing.
Transformer room is a place provided to accommodate transformer, O.S.F. and main feeder pillar to ensure its security and safety. Size of transformer room: –
The room should have clear and proper access, and proper ventilation. All trenches are provided with non-flammable covers. It should be well equipped with fire fighting equipment.
Transformer: – Transformer is a device which steps up/ steps down the voltages from the incoming source in a safe manner. There are two types of transformers dry & oil filled type. When transformer is provided in basement, Dry type transformer is mandatory.
Transformers are available in following ratings:
|Sr No.||Capacity in KVA||Length in mm||Width in mm||Height in mm||Weight in Kg|
O.S.F. (oil switch fuse): – The function of O.S.F. or S.F.U. is to provide a cut off and protection for transformer. They are available in following ranges: –
Main Feeder Pillar With ACB: – M.F.P distributes the electrical load through the terminals. It has one incoming terminal and remaining are outgoing terminals, through H.R.C. fuse. Air circuit breaker cuts-off the supply, in case of failure of the other circuit breaker.
R.M.U. (Ring Main Unit): – R.M.U. works as a change over switch for two high-tension supply lines of which one is taken as a standby.
Meter Room: – Meter room is a place, which accommodates the electrical meters, with the necessary distributions made through bus bar. Meter room should be easily accessible and safe. It should have proper ventilation and lighting. It should be always locked to avoid mishaps. It should be planned for easy movement of atleast one person.
Earthing: – Earthing is a circuit, which provides the connection between leaking electrical current and mass of earth. It is a safety measure to avoid mishaps due to leakage of current. The types of earthing depend on the resistance of the soil and required safety level of the device to be earthed.
Minimum earthing points: –
|Sr no.||Description||Minimum earth points|
|2||Meter room||3 Nos.|
Bus Bar: – The Busbar is a distribution box with copper strips and H.R.C. fuse (High Rupture capacity fuse). From the feeder pillar, main supply is provided to bus bar. Required tapings are provided to electrical meters. Proper earthing is necessary for bus bar. Different capacities of busbar are 100 A, 200A & 400A.
Under ground Cable Network (Ducting): – After finalizing the locations of the substation, L.T. feeder pillar, meter rooms, generators, pump house, street lighting, the underground cabling network plan is to be finalized.
Following points should be considered while finalizing the underground cabling network layout.
It is necessary to use well-laid and properly jointed RCC Hume pipe of specified diameter for cable ducting network. The RCC pipes should be laid atleast 1.2m below the finished road level. It is necessary to provide chambers of adequate size, to have proper space for cabling through RCC Hume pipes.
Location of chambers is decided as per : –
To safeguard the wires and to avoid any mishap, they are run through P.V.C. conduits, Types of conduit wiring are: –
Concealed conduit wiring: – This type of wiring is preferred over open type conduiting because,
|Sr No.||Fittings||Height From FFL|
|1||Bell push||1.5 m|
|2||Switch board||1.5 m|
|3||Light point on wall||2.4 m|
|4||T.V./Phone/5A point||0.75 m|
|5||Exhaust fan point||2.1 m|
|6||Boiler point||2.4 m|
|7||Main D.B.||2.4 m|
|8||Fridge point||1.5 m|
|9||Window A/C point||1.5 m|
|10||Washing machine point||1.5 m|
Minimum Electrical Points required : –
|Sr No||Rooms||Approx Area||Light Point||Fan Point||Power Point||Plug on main board||Plug Point||Exhaust Point|
|1||Living room||Upto 150 sft||2||1||1||2||1||1||1|
|2||Dinning||Upto 80 sft||1||1||1|
|3||Kitchen||Upto 80 sft||2||1||2||1||1||1|
|4||Master bed||Upto 140 sft||2||1||1||1||1||1||1|
|5||Common bed||Upto 130 sft||2||1||1||1|
|6||Balcony/Terrace||Upto 100 sft||1|
|7||Toilet||Upto 40 sft||1||1||1||1|
(for washing m/c)
Power Requirement for Some of The Important Household Appliances: –
Sizes of Wires For Various Purposes :-
|Supply (From – To)||Type of Supply||Size of wire used||colour of wire|
|Mains- (Meter room to D.B.)||Phase I||4 mm2 (7/20)||Red|
|Phase II||4 mm2 (7/20)||Yellow|
|Phase III||4 mm2 (7/20)||Blue|
|Neutral||4 mm2 (7/20)||Black|
|Sub main (D.B. to Switch board)||Earth||1 mm2 (1/18)||Green|
|Phase||2.5 mm2 (3/20)||Red|
|Neutral||2.5 mm2 (3/20)||Black|
|Points (Switch Board to Terminal)||Earth||1 mm2 (1/18)||Green|
|Phase||1 mm2 (1/18)||Red|
|Neutral||1 mm2 (1/18)||Black|
LOAD CALCULATIONS: – (Example)
Total Buildings – 3 nos. of P+7 storied All 2BHK flats with 28-flats/ building. Standard Points per flat :-
|Sr No||Rooms||Bell Point||Light Point||Fan Point||Power Point||Board Plug||Plug Point||Exhaust Point|
Building landing: – 8 light points
Terrace: – 2 light points
M/C room: – 1 light point
Entrance foyer: – 3 light point
Parking: – 8 light points
Streetlight: – 14 light point
Lift: – 7.5 HP
Bulkhead: – 8 nos.
Lift cabinet: – 1 light point
|a)||Load per flat|
|1) Light point – 13nos x 40W||= 520W|
|2) Fan point – 8nos x 50W||= 400W|
|3) Power point: –|
|b)||A.C. point – 1 x 1500W||= 1500W|
|c)||Geyser point – 2 x 2000W||= 4000W|
|d)||Fridge point – 1 x 200W||= 200W|
5A point – 14nos x 200W
= 9.42 KW per Flat.
Apply diversity factor of 0.6 = 0.6 x 9.42KW
= 5.652KW per Flat.
TOTAL = 7.435KW
= (28 x 5.652 + 7.435) KW
Applying overall diversity factor as 0.70 load will be; Load = 497.07 x 0.7
= 347.94KW Say 348KW.
. : Transformer capacity = 348KW
= 435 KVA = 435
= 483.33 KVA Say 483KVA
Norms For Constructing a Building In The Vicinity Of High-Tension Lines: –
|Description||Minimum clear vertical distance in meters||Minimum clear distance in meters|
Low and medium
|2.50 m||1.20 m|
High voltage lines
1) Up to 11KV.
2) Above 11KV &
up to 33KV.
|Ø||Wiring on the surface|
|Ø||Wiring under the surface|
|Ø||Wiring in surface conduit|
|Ø||Wiring in concealed conduit|
|Ø||Wiring going upwards|
|Ø||Wiring going downwards|
|Ø||Wiring passing vertically through room|
|Ø||Lighting fuse-board without switches|
|Ø||Lightning fuse-boards with switches|
|Ø||Distribution fuse-board without switches|
|Ø||Distribution fuse-board with switches|
|Ø||Power fuse-board without switches|
|Ø||Power fuse-board with switches|
|4.||SWITCHES AND SWITCH-OUTLET|
|Ø||One-way single pole switch|
|Ø||One-way two pole switch|
|Ø||Socket-outlet, 15 A|
|Ø||Combined switch and socket outlet, 5A|
|Ø||Combined switch and socket outlet, 15A|
|8.||LAMPS AND LIGHTINING APPRATUS|
|Ø||Lamp or outlet for lamp|
|Ø||Lamp mounted on wall|
|Ø||Lamp mounted on ceiling|
|Ø||Fixture with built in switch|
|Ø||Bulk head lamp|
|Ø||Water tight lighting fitting|
|9.||BELL, BUZZERS AND SIRENS|
|Ø||Horn or hooter|
|Ø||Socket for telecommunication apparatus|
|Ø||Radio receiving set|
|Ø||Control board for public address|
|Ø||Manually operated fire alarm|
|Ø||Automatic fire detector switch|
|Ø||Fire alarm indicator|