Estimation
It is the method of calculating the expenditure to be incurred on a particular job or process.

Overestimate
The estimate exceeds the actual result.
Ex: estimate 10000, actual 9000

Underestimate
The estimate fall short of the actual result.
Ex: estimate 10000, actual 12000

Hand book/Pocket Reference
It is a book with collection of instructions that is intended to provide ready reference.
Ex: Parry’s cheorikal hand book for engineers, Mark standard hand book for machine engineer, CRC hand book of chemistry and physics.

Reference Table
An information table that is used as a quick and easy reference for things that are difficult to remember such as comparing imperial with metric measurements.

Steps in Estimation
Estimating
$\displaystyle \small \bullet$ Determine the items and quantities required, their availability and transportation of materials
$\displaystyle \small \bullet$ Consult the rate catalogues for pricing the various items
$\displaystyle \small \bullet$ Assess the exact number of workers required to complete the job consulting the schedule of labour rates published by Govt.
$\displaystyle \small \bullet$ Add supervision charges and executor's profit
$\displaystyle \small \bullet$ In case of Govt. organization, where the work is to be executed by the contractor, the tenders are floated only after correctly specifying the description of each item
Drawing
$\displaystyle \small \bullet$ The necessary drawings of the building with dimension are required
$\displaystyle \small \bullet$ For the electrical installation the layout of the wiring should be shown on a separate drawing along with the position of the points
Specification of Materials
$\displaystyle \small \bullet$ Specification gives the details of materials, brand name, grade of quality, rating of current and voltage, quality certification like BIS or ISO etc.

Electrical Installation
$\displaystyle \small \bullet$ Complete specifications giving the general scheme of the installation, type of wiring and quality of materials.
$\displaystyle \small \bullet$ Plans and sections marked with details with the position of main switch gear and distribution boards.
$\displaystyle \small \bullet$ Earthing should be done as per IS specifications.
$\displaystyle \small \bullet$ Each circuit is to be protected against excessive current by fuse or automatic circuit breaker.
$\displaystyle \small \bullet$ Extra super voltage cables are used for 132KV lines.
$\displaystyle \small \bullet$ The wiring work should follow IE Rules 1956
$\displaystyle \small \bullet$ After completion of work the installations are to be tested before energisation.

Construction/Machining
$\displaystyle \small \bullet$ The machining estimation sheet includes raw material costs.
$\displaystyle \small \bullet$ Total cost includes raw materials cost and machining cost.
$\displaystyle \small \bullet$ The percentage of water absorbed by a good building stone should be less than 5%.
$\displaystyle \small \bullet$ The relative permittivity of rubber should be between 2 and 3.

Determination of Conductor Size
Current carrying capacity
$\displaystyle \small \bullet$ In any circuit the value of the current will be more as compared to sub - circuits.
$\displaystyle \small \bullet$ In sub circuits as the load decreases, the current is also reduced.
$\displaystyle \small \bullet$ It is very necessary to divide the services into groups in accordance with the amount of current which will flow through them.
Voltage drop
$\displaystyle \small \bullet$ Voltage drop is there as when the current flows through the wiring  and the same should be as low as permissible and economical.  
$\displaystyle \small \bullet$ The voltage drop can be determined by Ohm's law.  
$\displaystyle \small \bullet$ The voltage drop  will be less if the area of wire is more.
Minimum permissible size
Wire : The area of aluminium wire should not be less than 1.5 sq.mm and its single strand should not be less than 1.40 mm diameter.
U/G Cable : The area of conductor for two core cable should not be less than 6 sq.mm and for 25 sq.mm. The area of conductor for three and half cores cable should be 50 sq.mm or more.
A.C.S.R (Aluminium Conductor Steel Reinforced Cable): Total area of cross section should be 20-71 sq.mm.