Wire/CableAllowable Current Calculation Formula
The maximum continuous current that flows in an insulated wire is called allowable current. This value is calculated from the permissible rise in temperature during continuous use, ambient temperature, and wiring conditions as follows:
a) Allowable current in Junkosha Fluoropolymer Wires is given by:
b) How to calculate allowable current of wires & cables
First, based on the previous calculation, estimate temperature Τ[℃] meeting Ρ_{a} = Ρb, and then calculate allowable current I using P at this estimated temperature. The graphs (121~128) in the next section show I values calculated for typical wires and cables. The notation “at atmospheric pressure” means that temperature rises when wire is laid horizontally in the air at 20℃ with no airflow (no wind).

Determine the “rise in conductor temperature” (ΔΤ) based on ambient temperature, upperlimit temperature rise due to other adjacent components, or maximum continuous operating temperature for the insulation or conductor. Typically, the rated temperature of the wire is taken as the upperlimit temperature.
Table 121 Maximum continuous operating temperature for wire material
 Read current [A] directly off of the graph by erecting a perpendicular to the xaxis at a given point of ΔΤ (rise in conductor temperature provided in ①) until it hits the conductor outer diameter line or wire type line.
 Allowable current in a vacuum is about 1/2 to 1/3 that under atmospheric pressure. Figure 122 shows examples of calculation. For use in highpressure gas and under low pressure at high altitudes, multiply the correction coefficients shown in Figures 129 and 1210, respectively, by the value for atmospheric pressure.
 For use in the form of a bundle of many wires or cables, or in a parallel configuration, multiply the correction coefficient for the bundle.
 For use at high frequency (400Hz or higher), multiply the correction coefficient for AC resistance √(1/Ks) by the current value read in the figure.
 For such conductors as copper alloy wires for which conductivity constants are not 100%IACS, multiply the correction coefficient for conductivity (%IACS) √(Conductivity/100) by the current read in the figure.
Allowable Current
 Increases as the conductor crosssectional area becomes larger;
 Increases as pressure rises, and decreases as pressure falls; when in a vacuum, it is about 1/2 to 1/3 the value under normal atmospheric pressure;
 Increases in Junkosha Fluoropolymer Wires which have a larger ΔΤ; In other words, it is possible to make the crosssectional area of them smaller when the same allowable current is desirable; and
 Little depends on the type or thickness of insulation when ΔΤ is the same; the current read from the conductor outer diameter or crosssectional area can be used as is even when the insulation thickness is somewhat different.
c) Allowable Current Calculation
Figure 121 Allowable current of hookup wires for appliance wiring under normal atmospheric pressure
Figure 122 Allowable current of hookup wires for appliance wiring in a vacuum
Figure 123 Allowable current of hookup wires (stranded conductor) for
appliance wiring under normal atmospheric pressure
Figure 124 Allowable current of ultrafine wires
Figure 125 Allowable current of MILDTL16878 wire (solid conductor)
under normal atmospheric pressure
Figure 126 Allowable current of MILDTL16878 wire (stranded conductor)
under normal atmospheric pressure
Figure 127 Allowable current of robot cable (A type) under normal atmospheric pressure
Figure 128 Allowable current of robot cable (C type) under normal atmospheric pressure
Figure 129 Coefficient of increase in allowable current in highpressure gas
(measured by Junkosha)
Figure 1210 Allowable current correction coefficient at high altitudes in air
[based on SAE  AS50881 (formerly MILW5088L)]