cable calcs

[Corpy76]

Need advice, I'm doing design calcs for ring final circuits for the 2396 course. the question is when calculating the cable length for a ring circuit is it the total length of the circuit ie cu back to cu or to the furthest point on the ring or the mid point!

thanks in advice

 

[Richard Burns]

433.1.204 specifies the requirements for a ring final circuit in terms of the cable specifications.

Generally it may be considered that there a 20A load at the mid point and a further 12A evenly spread around the ring as stated in the OSG section 7.2.

32A rings are also often identified as covering a maximum of 100m² area, though this is a bit of a fudge but is specified in appendix 15.

 

[Lucien Nunes]

Think about the path the current would take according to where the load is. Doing an end-end continuity test you'll see the full length of the cable, but under working conditions load current will not flow from around the ring and back to itself. How many and how long are the cables feeding the hypothetical 20A load in the middle that richard mentions? If you assume everything to be symmetrical, you only need to consider one half as no current will flow past the midpoint, so with the other 12A split equally between the two halves you can calculate VD etc.

 

[GEOFF S]

Need advice, I'm doing design calcs for ring final circuits for the 2396 course. the question is when calculating the cable length for a ring circuit is it the total length of the circuit ie cu back to cu or to the furthest point on the ring or the mid point!

thanks in advice

Hi

I would say the total length is from one end to the other.

Cheers