How to select electrical wire size | How to select wire size for house wiring | How to select wire size for motor
In industry or commercial or resident wiring work one most important part of the work is selection of suitable electrical wire size.
So here we discuss about How to select electrical wire size,How to select wire size for house wiring, How to select wire size for motor or any circuit.
After reading this article i am sure you able to select a suitable cable for your application.
Information in this article will enable the wireman to select the correct cable under normal working conditions.
Content :
1) Factors for selection of cables
2) Types of protection based on current carrying capacity
3) Size and number of strands available in copper and aluminium cables and their current carrying capacity
4) Rating factor and determine the current capacity of cables with respect to temperature
5) Differentiate between solid and stranded conductors
6) Current rating of flexible stranded wire(conductors)
Selection of cables :
The current carrying capacity of a particular area of cross section cable depends upon the following factors.
• Type of conductors (metal)
• Type of insulation
• Cable run in conduit or in open surface
• Single or three phase circuit
• Type of protection - coarse or close excess current protection
• Ambient temperature
• Number of cables in bunches
Current rating of cables based on type of protection
Cables insulated with PVC, may sustain serious damage when subjected, even for relatively short periods, to higher temperature than the temperature permissible for continuous operation.
Therefore, current ratings of cables insulated with PVC are determined not only by the maximum conductor temperature admissible for continuous rating but also by the temperature likely to be attained under conditions of excess current.
Hence, the current rating of cables are given under two headings:
• cables provided with coarse excess current protection
• cables provided with close excess current protection.
Coarse excess current protection
In this type of protection, circuit protection will not operate within four hours at 1.5 times the designed load current of the circuit which it protects.
The devices affording coarse excess current protection include:
• Fuses which are having a fusing factor exceeding 1.5 times the marked rating.
• Carriers and bases used in rewirable type electrical fuses.
Close excess current protection
In this type of protection the circuit protection will operate within four hours at 1.5 times the designed load current of the circuit which it protects.
Devices include:
• Fuses fitted with fuse links having fusing factor not exceeding 1.5 times the marked rating
(HRC & cartridge etc.)
• Miniature and moulded case circuit breakers.
• Circuit breakers set to operate at an overload not exceeding 1.5 times the designed load current of the circuit.
Electrical inspectors, who are assigned by the Government to test installation and give permission for effecting supply, now recommend close excess current protection devices like MCB and HRC fuses to be included in the circuit for safety to the user and to reduce fire accidents.
Rating factor with respect to protection:
For circuits with coarse excess current protection (rewirable fuse unit) current rating of cables is given in Table 1.
Though the cables can carry a higher value of current than the current notified in the Table 1, for circuits having coarse excess current protection, the permissible current in cables is obtained by multiplying the normal current capacity by a rating factor of 0.81,
whereas for circuits protected by close current protection the normal current capacity is multiplied by a rating factor of 1.23.
 |
| Current rating for single core PVC insulated sheathed copper and aluminium conductor cables of size 1 to 50 sq. mm at ambient temperature of 40°c (Refer to IS 694 Part I -1964) TABLE 1 |
The following example will clarify the above information.
Normal current carrying capacity of 1.5 sq mm copper cable = 16 amps (normal rating)
Current capacity of the same cable when protected by
coarse excess current protection (Rating factor 0.81) = Normal capacity x Rating factor
= 16 x 0.81
= 13 amps.
Close excess current protection (Rating factor 1.23) = Normal capacity x Rating factor
= 16 x 1.23 = 19.7
= 20 amps.
Rating factor for ambient temperature :
Further the current rating of cables is greatly affected by the ambient temperature. As such if the ambient temperature
Example
Find the current rating of 2.5 sq mm, aluminium cable at 50°C. The circuit is single phase AC, protected by rewirable fuses and the cable is run in conduit.
Solution
The protection is coarse excess current protection.
Hence referring to Table 1 the current rating of 2.5 sq mm aluminium cable at 40°C is = 11 amps.
Rating factor at 50°C referring to Table 2 = 0.94.
The current rating of 2.5 sq.mm aluminium cable protected by coarse excess current protection run in conduit and at ambient temperature of 50°C = 11 x 0.94 = 10 amps.
This is my view on How to select electrical wire( cable) size after doing research on this topic form standard books.Hope you like please comment query regarding this.
thank you.
This is dummy text. It is not meant to be read. Accordingly, it is difficult to figure out when to end it. But then, this is dummy text. It is not meant to be read. Period.
1 comments:
Click here for commentsYour blog is very valuable which you have shared here about electrician can fix frayed wires. I appreciate your efforts which you have put into this article and also it is a gainful article for us. Thank you for sharing this article here. Custom Fabrication
ConversionConversion EmoticonEmoticon