If I wanted to calculate the maximum length of a circuit, in relation to its Zs
would the following transposition be correct..
So if it was a 2.5mm2 T&E cable on a 20 amp MCB.
I would use 2.19Ω (BS7671) as my Max Zs, as this is at the maximum operating temperature. Not 1.75Ω as in the 80% value
I have a Ze of 0.35
Im correcting the 19.51 mΩ/m to 70 oC with the factor of 1.2
R1+R2 = 19.51
L = Length
F = Temperature correction 1.2
Zs = Ze + (R1+R2) x L x F / 1000
2.19 = 0.35 + 19.51 x ? x1.2 /1000
Transposed to
L= Zs - Ze / R1+R2 x F
x 1000
So...
2.19 -0.35 = 1.84
19.51 x 1.2 = 23.41
1.84 / 23.41 = 0.07
0.07 x 1000 = 70m
But this would give a volt drop of 25.2 volts.
If my maths are correct !! I presume in the design stage, using Zs as a guide to maximum length of a circuit, is not a good idea?
I hope that makes some sense...
Thanks
would the following transposition be correct..
So if it was a 2.5mm2 T&E cable on a 20 amp MCB.
I would use 2.19Ω (BS7671) as my Max Zs, as this is at the maximum operating temperature. Not 1.75Ω as in the 80% value
I have a Ze of 0.35
Im correcting the 19.51 mΩ/m to 70 oC with the factor of 1.2
R1+R2 = 19.51
L = Length
F = Temperature correction 1.2
Zs = Ze + (R1+R2) x L x F / 1000
2.19 = 0.35 + 19.51 x ? x1.2 /1000
Transposed to
L= Zs - Ze / R1+R2 x F
x 1000
So...
2.19 -0.35 = 1.84
19.51 x 1.2 = 23.41
1.84 / 23.41 = 0.07
0.07 x 1000 = 70m
But this would give a volt drop of 25.2 volts.
If my maths are correct !! I presume in the design stage, using Zs as a guide to maximum length of a circuit, is not a good idea?
I hope that makes some sense...
Thanks