I have a question i hope someone can just give me a little clarification on .
When carrying out preliminary cable design for a given circuit we use this formula = ( milliohms per metre x Length x multiplier Factor for maximum operating temperature ).
Do we still need to use the the maximum operating temperature factor for the given cable type in the above formula if we use the Zs measured value (the 80% rule ) against the protective device .
example
A Radial circuit is wired in 2.5mm 1.5mm , the Length is 25M the Calculated value by design would be ( 19.51 x 25 x factor 1.2 ) divided by 1000 which would = ( R1+R2) as 0.58 Ohms obviously add this value to the Ze and then check against the protective device Zs measured value ( 80% rule ) to confirm is this value complies .
or would we just use the formula this way ( 19.51 x 25 ) divided by 1000 = ( R1+R2 ) = 0.48 ohms added this value to the Ze then check against the Zs measured value of the protective device .
Do we still use table I1 from the on site guide page 220 when calculating by design the R1+R2 or is this not used because of the 80% rule applied to protective devices Zs .
When carrying out preliminary cable design for a given circuit we use this formula = ( milliohms per metre x Length x multiplier Factor for maximum operating temperature ).
Do we still need to use the the maximum operating temperature factor for the given cable type in the above formula if we use the Zs measured value (the 80% rule ) against the protective device .
example
A Radial circuit is wired in 2.5mm 1.5mm , the Length is 25M the Calculated value by design would be ( 19.51 x 25 x factor 1.2 ) divided by 1000 which would = ( R1+R2) as 0.58 Ohms obviously add this value to the Ze and then check against the protective device Zs measured value ( 80% rule ) to confirm is this value complies .
or would we just use the formula this way ( 19.51 x 25 ) divided by 1000 = ( R1+R2 ) = 0.48 ohms added this value to the Ze then check against the Zs measured value of the protective device .
Do we still use table I1 from the on site guide page 220 when calculating by design the R1+R2 or is this not used because of the 80% rule applied to protective devices Zs .
