Cable Sizing

Check out the latest edition of the Wiring Regulations, published by the Institution of Electrical Engineers.

Dear sojinrin

You should in general take into account the following major factors

i. the current rating of the cable you choose which also takes into account the ambient temperature and other environmental factors: the cross sectional area mm.sq. will be decided by this and factor ii) below. Note: a cable's temperature will rise above ambient by a fixed amount when allowing a certain amount of current in it.

Therefore, if the ambient is high then you will need to select higher current rating cable to enable it to stay cool. Mfrs specify the max conductor temp at a certain ambient for the stated ampacity. Example: If the cable you select is allowing 27 amps continuously at 40 deg C ambient you will need to select a 2.5 mm sq copper cable(see table 6 here)

The temp mentioned here 85 deg C is conductor temperature, beyond that the PVC insulation will fail, become brittle etc.

ii. the voltage drop for the size you have chosen that depends on the distance between source and point of use. If the drop exceeds the power supply tolerance of the equipment you are supplying electric power to then you may need to choose the next higher mm sq size for your cable.

iii. the type of cable will depend on the installation location. e.g where you expect the cable to be subject to mechanical abuse you may need to choose cable with armored protection and so on.

iv. the voltage rating will determine the type (and thickness) of insulation used in the cable.

There are several "electrical handbooks" that will provide more information

I hope this information is useful.

Sridhar Chitta

Nice reply! Just couldn't help myself putting something in print!

Thank you Mr. Truman. I assume you were complimenting my reply !

You can be sure on that!

Hello

I have answered your Post/comments,

Generally best to use the Cable Maker of your particular cable, but try:

http://relemaccables.com/

If you are still needing help, reply with

Kind Regards....

You will also have to take into consideration the environment it passes through! Is there a likelihood that the cable will need armour casing, Will it need to be double insulated, open to the elements, under hot sun all day, with other cables and so on!

Sizing the cable is one thing, protecting the cable is another! Many people forget about the physical abuse the cable gets if it is driven over by a lorry on a gravel road! All I am saying is make sure your cable is designed for the location it is placed in! A normal multi cored cable will not be adequate if there is a chance it could be trapped in a sliding door, eaten by a dog, or slowly worn away by the vibrating of a machine!

There are many sites that can help you understand the basic principals of electricity, but they are for just that, basic electricity, look for the possible faults that may occur due to rubbing, crushing, sharp edge on a panel! Expect the faults to happen if you don't plan for them!

Apart from that, why not call an electrician!

Refer to any good hand book on Electrical Engineering.Better and easier way is to use manufacturers data.Siemens did have a catalog.Other cable manufacturers should be able to provide their data and selection procedure with formulae

I've written about this before. A good utility is free to download from here:

http://www.generalcable.co.nz/newzealand/NZDownloads/Gencalc.aspx

This suits New Zealand conditions only (very similar to UK)!

I know it hurts financially, but always be generous to cables!

Unless i have missed it, I don't think anyone has mentioned customer specifications yet. Always ensure that whatever the rules tell you to do, the customer has not for some reason increased the demand for safety or any other field. You don't wanna have something rejected for having followed the correct procedure but forgot to consult the customer.

Good luck and don't poke anything.