How To Select Cables

Choosing a proper and an adequate wire or cable for any purpose is of very much importance. And if you are choosing it for the electrical purpose then it is of utmost value to give proper care and attention. Different electrical appliances require different current and voltage requirements to operate. So for different devices the cable used should also be different. Selecting the proper cable is of so much importance because it is connected with the security of your house or other buildings.

Important points to take care of before purchasing a electrical cable:
In selecting a wire or cable for primary and secondary power circuits certain requirements should be kept in mind. They are:

• Type of Installation
• Voltage Rating
• Ampacity Requirements
• Heating Conditions
• Special Conditions

Type of installation
The method you are going to follow to install a cable is a determining factor for the selection of cable. You may use the cable in underground applications, outdoor applications, or indoor applications. In each of these applications the requirement of cables are different. You must give attention towards some particular points.

• Outdoor applications: For outdoor applications the cable is directly buried under ground or installed in over head racks. In underground wiring the cables are too prone to prevent it from moisture. Once moisture enter the cable it will create problems in long running of cable. So the cables selected should be suitable for wet installation conditions.
  
  
• Indoor applications: Cables used in indoor applications are either installed in conduit or in over head racks. The interlocked armor cable is a useful option today. It is very demanding and advantageous as well. The armor rectifies the requirement of a conduit and it is totally a self contained unit. Besides its specific advantages it need 20 to 50% less cost requirement than the traditional conduit system.

Voltage requirement
The voltage determination for the electrical device is necessary because it guide you in buying the proper cable. The type and thickness of insulation is determined by the voltage factor. It also helps in determining the minimum size of conductor that is suitable for small loads. Besides that it is also important to know that whether grounded or ungrounded neutral is used.


Ampacity requirements
Determining the final conductor size require the ampacity of KVA loading. The power factor, current load, and KVA load should be known prior to finalize the size of conductor. Sometimes the cable size is determined by voltage drop rather than only by heating. In any uncertain situations the size is determined separately by voltage drop and by heating, and then the bigger size must be chosen.

Heating conditions
Heating conditions include the external thermal conditions which are responsible for determining the temperature increment of a cable. The external factors affect the lasting and proper functioning of cables. Some important factors which affect the selection of cables:

• Ambient Temperature
• Presence of Artificial Cooling
• Number of Cables in a Duct Bank
• Proximity to other Cables
• Thermal Conductivity of Soil or other Surrounding Medium
• Depth of Buried Cable
• Nature of Surrounding Atmosphere

Special conditions
Except all the conditions and situations we discussed here, there may be some other special conditions which might affect the performance of a cable. You must also consider those points to ensure the better life of your cables. Some of the common conditions are:

• Presence of boilers, steam pipes or other big source of heat.
• Effect of magnetic material like pipes.
• Presence of corrosive substance in the surrounding.
• Interference occurring in telephone cables due to adjacent power cables.

Some buying tips for cable and wire purchasing
While preparing for giving the final order for wire or cable you must be sure of the following information so that you get the correct material.

• Voltage Rating: If the voltage rating is above 5000V, check whether cable is shielded or not. In case of voltage rating like 8000V, 15000V, 25000V or 30000V, will the cable be provided grounded neutral or ungrounded neutral.
  
  
• Conductor type and size: The size and type of conductor used in these cables must be known.
  
  
• The type of insulation: There are various materials used for insulation of wires and cables and some are specific to particular types of uses. So the type of insulation must be known before purchasing.
  
  
• Type of protective covering: Different cables need different types and levels of covering. It is very much dependent on the use of cables. So you should know about the covering of cables.
  
  
• Total length of each item and individual cutting length desired: The total length of the cable should be known before the purchase so that you may be confirmed that how much bundles or packets you have to order.
  
  
• Delivery requirements: The timely and safely delivery of the goods is of much importance and you should be confirmed about that before finalizing the deal.