Current rating standards 69-30 PT III
Sustained current ratings for 600/1000 V & 1900/3300 V cables with 70oC thermoplastic insulation (ac 50 Hz and dc)
This report, which is Part III of a series, provides current ratings for 70 °C thermoplastic insulated cables. Ratings given in this report are based on the cable dimensions in BS 6346:1969. These ratings are also considered to be applicable to cables having a similar construction.
Ratings are given for cables installed direct in the ground, in underground ducts and in air. The conductor temperature limit of 70°C, on which ratings are based, has been adopted on the recommendations of British cable manufacturers. Ambient temperatures adopted for tabulation are values suitable for most UK installations.
Attention is drawn to the fact that the use of the ratings given in the tables is restricted to circuits provided with excess current protection whose designed minimum operating current does not exceed 1.45 x those ratings when the cables are run in air or in ducts and not more than 1.3 x those ratings when the cables are laid direct in the ground.
When the circuit protection does not comply with this requirement the cable required for a given continuous load current should be chosen in relation to (a) the tabulated ratings and (b) the minimum current at which the excess current protection is designed to operate, in accordance with the directions given in Section five.
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