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Symbols - Cables
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Discussion
b
circuit factor (=2 for d.c. and single phase, = 1 for three phase)
C
cable capacitance [ F, μF, F.m
^{-1}
]
d
_{c}
diameter of
conductor
, m
d
_{s}
mean diameter of
sheath
, m
I
_{2}
operating or tripping current of the protective device, A
I
_{b}
c
able design conductor current, A
I
_{c}
cable charging current [A, A.m
^{-1}
]
I
_{n}
rated current or current setting of the protective device, A
I
_{1}
,
I
_{2}
,
I
_{3}
conductor phase current of
L
_{1}
,
L
_{2}
and
L
_{3}
, A
I
_{s1}
,
I
_{s2}
,
I
_{s3}
sheath phase current of
L
_{1}
,
L
_{2}
and
L
_{3}
, A
I
_{t}
tabulated current rating for a particular installation condition, A
I
_{z}
sustained current rating of cable under particular installation conditions, A
L
cable inductance [H, mH, mH.m
^{-1}
]
L
_{s}
inductance of sheath, H.m-
^{1}
n
number of
circuit
in a group
R
cable resistance [Ω, Ω.m
^{-1}
]
R
_{20}
resistance of conductor at 20 °C
Rac
a.c.
resistance
of
cable
, Ω.m
^{-1}
R
_{armou}
_{r}
resistance of armour, Ω.m
^{-1}
Rdc
d.c.
resistance
of
cable
, Ω.m
^{-1}
R
_{s}
resistance of the sheath, Ω.m
^{-1}
R
_{t}
resistance of conductor at t °C
S
distance between cable centres, m
S
_{12}
distance of cable centres between
L
_{1}
and
L
_{2}
, m
S
_{23}
distance of cable centres between
L
_{2}
and
L
_{3}
, m
S
_{31}
distance of cable centres between
L
_{3}
and
L
_{1}
, m
t
conductor [cable] temperature, °C
T
_{a}
ambient temperature, °C
T
_{c}
conductor [insulation] limiting/design temperature, °C
X
cable reactance, general [Ω, Ω.m
^{-1}
]
X
_{c}
cable capacitive reactance [Ω, Ω.m
^{-1}
]
X
_{L}
cable inductive reactance [Ω, Ω.m
^{-1}
]
X
_{1}
,
X
_{3}
,
X
_{a}
,
X
_{b}
reactance formulas; sheath induced voltage, Ω.m
^{-1}
X
_{m}
mutual reactance between conductor and sheath, Ω/unit length
X
_{s}
sheath reactance, Ω.m
^{-1}
Uo
nominal voltage, V
U
_{s}
sheath voltage, V
U
_{1}
,
U
_{2}
,
U
_{3}
phase voltage o f
L
_{1}
,
L
_{2}
and
L
_{3}
, V
U
_{s1}
,
U
_{s2}
,
U
_{s3}
sheath inductive phase voltage o f
L
_{1}
,
L
_{2}
and
L
_{3}
, V
Z
cable impedance [Ω, Ω.m
^{-1}
]
ΔU
voltage drop,
ϵ
_{o}
permittivity of free space = 8.854187819x10
^{-12}
F/m
ϵ
_{r}
relative permittivity of a dielectric
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