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 |