T.O. 33B-1-1
4-7
4.2.2.1.1.3 Measurement of Conductivity.
Electrical conductivity is the reciprocal of electrical resistivity. The reciprocal of the "ohm" is commonly called the
"mho". Conductivity is commonly expressed in units of mhos per unit length such as mho/inch or mho/meter. The
relationships between conductivity, resistivity and resistance are expressed by the following equations:
s
r
=
=
L RA
/
/
1
; therefore, R
L A
= r
/
Where:
s = electrical conductivity (mhos/unit-length)
L =
length
R =
resistance (ohms)
A =
cross-sectional area
r = resistivity (ohms–unit-length)
*
See Table 4-3 for more aluminum alloy materials.
**
Values represent averages taken from literature.
4.2.2.1.1.4 Conductivity based on %IACS.
An alternative way of expressing conductivity is as a percent of the conductivity of a known material. The
International Electrotechnical Commission has designated the conductivity of a specific grade of high purity copper to
be the standard for this alternative method with a conductivity of 100 percent. It is called the International Annealed
Copper Standard (IACS). The conductivity’s of all other metals are then expressed as a percentage of this standard.
Average values of conductivity of some commonly used engineering materials are listed in Table 4-3.
