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Thermocouple and
Extension Wire
-
General lnformation
,i
t:
1 , ,'
r ::,
lrll
Therrnocouple
Wire
-
Thermocouple
grade
wire
is
typically
used
to
make
the
actual
thermocouple
element.
Note
that
thermocouple
grade
wire
can
be
used as extension wire,
but
the
outer
jacket
insulation may have a different color code and in some cases
it
may be much more expen-
sive than using exlension
grade
wire.
Depending on
the
applications service
temperature
range, environmental conditions,
and
phys-
ical constraints, a
wire
gauge, calibration
type, and
insulation material
can
be
specified.
Each of
the
calibration
types
have
their
own
insulation standard color code for
easy identification.
See the
thermocouple
wire color code table located
in
this
catalog.
To
aid
in
the
installation of the thermocouple, the RED wire is always the NEGATIVE leg of the
element. lf
the thermocouple wires are
installed
incorrectly
the instrument
in
the
circuit
will give backwards
readings.
Thermocouple
grade
wire
is offered
with solid or stranded
con-
ductors and
in a
wide
range
of
gauges.
lf
the thermocouple wire will be
in
an
application
where it
is
subjected to
repeated
flexing,
a
stranded
wire should be
used
to
prevent conductor
fatigue
and
failure.
Thermocouple wire
is
available
in
AWG
wire
gauges
from
40
(0.0031 inches)
to 6 (0.1620
inches) in bare wire
form or
insulated
with any
of
the common insulation
materials.
lnsulation
materials
for
thermocouple
grade
wire
are available
to
cover
temperature
ranges
from
-190"F to
2000'F
(-123'C to
1093"G).
Extension
Wire
-
Extension grade
wire is
used
to
complete
the thermocouple
circuit
from the thermocouple element
to
the temperature
instrument.
Note
that
extension
grade wire
should
not
be
used
to make thermocouple
elements.
Extension
wires can
be
divided
into two
categories. Category
1
extension wires are
made
with conductors which are the same as the
thermocouple.
Category
2
extension
wires are made with conductors which are different from the the
thermocouple.
The base metal thermocouples are used with Category
1
extension
wires.
Noble metal and a
few
nonstandardized thermocouples
are
used
with
Category 2 extension
wires.
The
extension
wire and thermocouple wire
musf
both
be
of
the same
calibration typelo
maintain
the accuracy
of
the thermocouple. The
polari-
ty
of
each
set of
wires
must also
be
maintained
during
installation in order for the
thermocouple
circuit to
function properly. The
RED
wire
is
always
the
NEGATIVE leg of
the
extension
wire.
Extension grade
wire
is
also color coded
to
help
with
identification
and
instal-
lation.
See
the
extension grade wire color code
table
in
this
catalog.
lf the extension wire
will
be subject
to
repeated flexing, a strand-
ed wire
should
be used
to
prevent
fatigue
and
failure.
For
typical,
non-flexing, ambient
temperature,
indoor use, a 20
gauge
(1
.3mm)
solid conductor
with
PVC insulation
wire
is an exceilent
choice.
Note:
Never install
extension
wire
in
the
same
conduit
as
power
lrnes.
This will cause
interference
and errors
in the
temperature
readings. lt
is
a good
practice
to
keep
the
extension
wire at least
1
foot away from power
lines
to
maintain
an
accurate
thermocouple
circuit.
Limits
of
Error
for
Thermocouple
&
Extension
Wire.
The
limits
of
error
for the
calibration
types listed
in
this catalog have been
extracted
from
standards
set
by the
American
National
Standards lnstitute,
lnc. as
shown
in ASTM Standard E
230.
All
thermocouple grade
and
extension grade
wire are tested
and
matched
in
our
own
calibration
laboratories
to
insure
that they
are within
these
standards
or
better.
Page
104