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Symbols - Cables

 b circuit factor (=2 for d.c. and single phase, = 1 for three phase) 
C cable capacitance [ F, μF, F.m-1]
dc diameter of conductor, m
ds mean diameter of sheath, m
I2  operating or tripping current of the protective device, A
Ib cable design conductor current, A 
Ic cable charging current [A, A.m-1]
In   rated current or current setting of the protective device, A
I1, I2, I3 conductor phase current of L1, L2 and L3, A
Is1, Is2, Is3 sheath phase current of L1, L2 and L3, A
It  tabulated current rating for a particular installation condition, A
Iz sustained current rating of cable under particular installation conditions, A 
L cable inductance [H, mH, mH.m-1]
Ls inductance of sheath, H.m-1
n number of circuit in a group 
R cable resistance [Ω, Ω.m-1]
 R20  resistance of conductor at 20 °C
Rac a.c. resistance of cable, Ω.m-1
Rarmour resistance of armour, Ω.m-1
Rdc d.c. resistance of cable, Ω.m-1
Rs resistance of the sheath, Ω.m-1
 Rt resistance of conductor at t °C
S distance between cable centres, m
S12 distance of cable centres between L1 and L2, m
S23 distance of cable centres between L2 and L3, m
S31 distance of cable centres between L3and L1, m
 t conductor [cable]  temperature, °C
 Ta ambient temperature, °C 
 Tc conductor [insulation] limiting/design temperature, °C 
X cable reactance, general [Ω, Ω.m-1]
Xc cable capacitive reactance [Ω, Ω.m-1]
XL cable inductive reactance [Ω, Ω.m-1]
X1, X3, Xa, Xb reactance formulas; sheath induced voltage, Ω.m-1
Xm mutual reactance between conductor and sheath, Ω/unit length
Xs sheath reactance, Ω.m-1
Uo   nominal voltage, V
Us sheath voltage, V
U1, U2, U3 phase voltage o f L1, L2 and L3, V
Us1, Us2, Us3 sheath inductive phase voltage o f L1, L2 and L3, V
Z cable impedance [Ω, Ω.m-1]
 ΔU voltage drop,
ϵo permittivity of free space = 8.854187819x10-12 F/m
ϵr relative permittivity of a dielectric


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