Information

Current-Carrying Capacity of Flat
Wires
For round wires the diameter is
sufficient to determine the data
previously quoted. For ribbons the
thickness and above all, the width
must be taken into consideration.
When making comparisons, the
table containing the cross-sectional
values of standard ribbons with
rounded-off edges vs. those of
round wires should be consulted.
At high temperature (600°C) or if for
other reasons the proportion of heat
dissipation by radiation exceeds the
dissipation by convection, flat wires
and ribbons of any dimension have
a current-carrying capacity greater
than that of round wires with an
equal cross-sectional area, due to
their larger surface area.
In the event that the heat
dissipation takes place mainly by
convection - generally at low
temperatures -, then the current
carrying capacity of flat wires and
ribbons will exceed that of flat wires
of an equal cross-sectional area
only for ratios between width and
thickness of more than 15 : 1.
page 10
If flat wires are wound around a
carrier there will be a larger contact
area available for heat transfer to
the carrier by heat conductance as
compares with round wires, but no
generally valid data can be given as
to a possibly higher current-carrying
capacity. For heat dissipation to the
outside, of course, only a part i. e.
one half of the surface of the ribbon
is available; this must be kept in
mind when making calculations.
The following tables give
information on the resistance,
surface and weight of flat ISOTAN
®
wires, referenced at 1 m. In addition
they contain data as to the load
currents for ribbons of ISOTAN
®
at
overtemperatures of 100/200/300
and 400°C.
The following should be mentioned:
Since the edges are rounded-off,
the cross-sectional area and
resistance of flat wires are
calculated by the formula below.
Calculation of the Cross-
Sectional Area and Resistance of
Flat Wires
R =
)215.0(
10
3
⋅−
⋅⋅
−
aba
l
ρ
Q =
)215.0(
⋅
−
aba
O =
lba
⋅
+
−
]2)2([
π
a = Thickness in mm
b = Width in mm
l = Length in mm
R = Resistance in Ω
Q = Cross-sectional area
in mm”
O = Surface in mm²
ρ
= Resistivity in Ω ⋅mm ⋅ m
-1
The values in the current-carrying
capacity tables refer to bare wired
or bare ribbon. Oxidized wire and
ribbon can, due to improved heat
dissipation, withstand a load
increase of up to 20 %, expressed
in Watt per cm
2
.
The current-carrying capacity of
ribbons of other alloys can be using
the same method as described for
wires.
Diameter of Round Wires of Equal Cross-Sectional Area in mm
thickness width / b in mm
a in mm 1 2 3 4 5 6 7 8 9 10
0,05 0,25 0,36 0,44 0,50 0,56 0,62 0,67 0,71 0,76 0,80
0,06 0,27 0,39 0,48 0,55 0,62 0,68 0,73 0,78 0,83 0,87
0,07 0,30 0,42 0,52 0,60 0,67 0,73 0,79 0,84 0,89 0,94
0,08 0,32 0,45 0,55 0,64 0,71 0,78 0,84 0,90 0,96 1,01
0,09 0,34 0,48 0,58 0,68 0,76 0,83 0,89 0,96 1,01 1,07
0,10 0,35 0,50 0,62 0,71 0,80 0,87 0,94 1,01 1,07 1,13
0,12 0,39 0,55 0,67 0,78 0,87 0,96 1,03 1,10 1,17 1,23
0,14 0,42 0,59 0,73 0,84 0,94 1,03 1,11 1,19 1,26 1,33
0,16 0,44 0,63 0,78 0,90 1,01 1,10 1,19 1,27 1,35 1,42
0,18 0,47 0,67 0,82 0,95 1,07 1,17 1,26 1,35 1,43 1,51
0,20 0,49 0,71 0,87 1,00 1,12 1,23 1,33 1,42 1,51 1,59
0,22 0,52 0,74 0,91 1,05 1,18 1,29 1,40 1,49 1,58 1,67
0,24 0,54 0,77 0,95 1,10 1,23 1,35 1,46 1,56 1,65 1,74
0,26 0,56 0,80 0,99 1,14 1,28 1,40 1,52 1,62 1,72 1,81
0,28 0,58 0,83 1,02 1,19 1,33 1,46 1,57 1,68 1,79 1,88
0,30 0,60 0,86 1,06 1,23 1,37 1,51 1,63 1,74 1,85 1,95
0,35 0,64 0,93 1,14 1,32 1,48 1,62 1,76 1,88 1,99 2,10
0,40 0,68 0,99 1,22 1,41 1,58 1,74 1,88 2,01 2,13 2,25
0,45 0,72 1,04 1,29 1,50 1,68 1,84 1,99 2,13 2,26 2,38
0,50 0,75 1,10 1,36 1,57 1,76 1,94 2,09 2,24 2,38 2,51
0,60 1,20 1,48 1,72 1,93 2,12 2,29 2,45 2,60 2,75
0,70 1,28 1,59 1,85 2,08 2,28 2,47 2,64 2,81 2,96
0,80 1,36 1,70 1,97 2,22 2,44 2,64 2,82 3,00 3,16
0,90 1,44 1,79 2,09 2,35 2,58 2,79 2,99 3,18 3,35
1,00 1,51 1,88 2,20 2,47 2,71 2,94 3,15 3,34 3,53
1,20 2,05 2,39 2,69 2,96 3,21 3,44 3,65 3,86
1,40 2,19 2,57 2,89 3,19 3,46 3,70 3,94 4,16
1,60 2,33 2,73 3,08 3,39 3,68 3,95 4,20 4,44
1,80 2,45 2,88 3,25 3,59 3,89 4,18 4,44 4,69
2,00 2,56 3,02 3,41 3,77 4,09 4,39 4,67 4,94
A = Thickness, b = Width