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# Cable Sizing - Derating factor

## Cable Sizing - Derating factor

(OP)
While calculating the derating factor we need to have the total no. of cables for finding group factor. Now to have the total no. of cables we need to have the derating factor. Please let me know how to proceed and which one shall be selected first. Thanx

### RE: Cable Sizing - Derating factor

I'd apply this method :
Suppose you have one cable only, this gives you a derating factor.
Based on this derating factor, calculate the current carrying capacity of the cable (or theoretical CSA). If this is OK, you have your solution.
Otherwise, use two cables, and get the new derating factor. Calculate the current carrying capacity (or theoretical CSA). If this is OK, you have your solution.
Otherwise, use three cables, ....
It's repetitive, but it works !
Software programs are good at handling this.

Good luck,

Boris

### RE: Cable Sizing - Derating factor

If u refer to the BS7671:1992 16th Ed., there is a table for u to refer to. it shud be a straight forward calculation. in addition, u also need to take into the surrounding temprature and installation method factors, which incidentally is included in the BS7671:1992 16th Ed. all this is in pg 188.  refer to table4. you can always complie this data and do a look up table calculation. alternatively, u can request from the cable supplier for this purpose.

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