Originally published on EcoStruxure Power Design Blog by Genghiz | November 10, 2020 08:59 AM
From the available inputs;
let us see how to determine the 'smallest allowable cross sectional area' of the circuit conductors.
Directly in Ground
*Some of the inputs are assumed to provide in this example; and they were neither received from the user, nor from the environment.
As the THDi is > 33 % (that is THDI = 48 %). So, the Size-determining" live conductor is Neutral
This circuit is assumed to be protected by the circuit-breaker.
So that the K3 =1.0
For 40°C and with the insulation XLPE. F1 = 0.85
There is no additional touching circuits i.e. total no. of circuits is 1
F2group = 1.00
THDI >45 % = THDI = 48 % à f3NeutralTHDI = 1.00
Installation method = in Ground -> Rth = 2.0 K.m/w
f3RthSoil = 1.12
Correction factor f
f = 0.85 × 1.00 × 1.00 × 1.05 × 1.00 = 0.952
The overall correction factor is determined by multiplying all 'the available correction factors."
Theoretical Iz’ = (K3 x IB) / (F x N live) = (1.0 x 288) / (0.952 x1) = 302.52 A = 303 A
The conductor selection is done from the given Table B.52.5 Column 8
185 mm2 will be able to carry 324 Amps
240 mm2 will be able to carry 375 Amps
Considering the +5% of tolerance, It would be recommended to consider the size as 185 mm²
K3(Correction Factor based on Protection Device)
F1(Correction Factor based on Temperature)
F2(Correction Factor based on Group of conductors)
F3(Correction Factor based on THDi)
F3(Correction Factor based on Soil Resistivity)
K user(Correction Factor defined by the user)
Iz (A) considered from the table
Theoretical cross sectional area Ph (mm²)
1 x 185 mm²
Theoretical cross sectional area Neutral (mm²)
Theoretical cross sectional area PE (mm²)
1 x 95 mm²
That's really informative answer.
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