Cable Voltage Rating

Clarify on your load.

First consequence, the cable with the lower rating current carrying capacity would be lower than the 'proper cable' hence might fail in use.

Dear Josej

first of all usually all the cables are checked by giving double of its rated voltage. if u need to use a cable on 600V servive it would be checked at 1200V. but it does not mean you start using this cable. such a amargin is given to withstand the voltage spikes in the line.

Dear friend,

If your project requirement of a cable is for 600/1000V, then accept only the cable with same voltage range. Half the rated cable offered by the vendor will not be suitable for your project. When the specification of cable is rated for specific voltage by the manufacturer it means that the insulation of the cable is capable of withstanding a voltage level specified with out insulation failure. The requirement of a cable with 1000 volts means the cable can be safely used with out insulation failure for 440 volts system. This is for considering the possible insulation failure due to the overvoltage and spike voltage that may arise in the circuit internally or externally due to various reasons.

<...What will be the technical conseq if I use 300V rating cable....>

If the circuit is 24VDC, absolutely none...