Transmission Techniques: Wire and Cable 407small, or how large, a conductor could be. Choice of size
(AWG) will be based on application and the current or
wattage delivery required. If jacketed, the choice of
jacket can be based on performance, ruggedness, flexi-
bility, or any other requirement.
There is no single conductor plenum rating because
the NEC (National Electrical Code) only applies to
cables, more than one conductor. However, Articles 300
and 310 of the NEC are sometimes cited when installing
single conductor wire for grounds and similar
applications.
14.8 Multiconductor
Bundles of two or more insulated wires are considered
multiconductor cable. Besides the requirements for each
conductor, there is often an overall jacket, chosen for
whatever properties would be appropriate for a particu-
lar application.
There are specialized multiconductor cables, such as
power cordage used to deliver ac power from a wall
outlet (or other source) to a device. There are UL safety
ratings on such a cable to assure users will not be
harmed.
There are other multiconductor applications such as
VFD (variable frequency drive) cables, specially formu-
lated to minimize standing waves and arcing discharge
when running variable frequency motors. Since a multi-
conductor cable is not divided into pairs, resistance is
still the major parameter to be determined, although
reactions between conductors (as in VFD) can also be
considered.
14.8.1 Multiconductor Insulation Color CodesThe wire insulation colors help trace conductors or con-
ductor pairs. There are many color tables; Table 14-10 is
one example.14.9 Pairs and Balanced LinesTwisting two insulated wires together makes a twisted
pair. Since two conductive paths are needed to make a
circuit, twisted pairs give users an easy way to connect
power or signals from point to point. Sometimes the
insulation color is different to identify each wire in each
pair. Pairs can have dramatically better performance than
multiconductor cables because pairs can be driven as a
balanced line.
A balanced line is a configuration where the two
wires are electrically identical. The electrical perfor-
mance is referred to ground, the zero point in circuit
design. Balanced lines reject noise, from low frequen-
cies, such as 50/60 Hz power line noise, up to radio
frequency signals in the Megahertz, or even higher.
When the two conductors are electrically identical,
or close to identical, there are many other parameters,
besides resistance, that come into play. These include
capacitance, inductance, and impedance. And when we
get to high-frequency pairs, such as data cables, we
even measure the variations in resistance (resistance
unbalance), variations in capacitance (capacitance
unbalance, or even variations in impedance (return
loss). Each of these has a section farther on in this
chapter.Table 14-10. Color Code for Nonpaired Cables per ICEA #2 and #2R
Conductor Color Conductor Color Conductor Color Conductor Color1st Black 14th Green/White 27th Blue/Blk/Wht 40th Red/Wht/Grn
2nd White 15th Blue/White 28th Blk/Red/Grn 41st Grn/Wht/Blue
3rd Red 16th Black/Red 29th Wht/Red/Grn 42nd Org/Red.Grn
4th Green 17th White/Red 30th Red/Blk/Grn 43rd Blue/Red/Grn
5th Orange 18th Orange/Red 31st Grn/Blk/Org 44th Blk/Wht/Blue
6th Blue 19th Blue/Red 32nd Org/Blk/Grn 45th Wht/Blk/Blue
7th White/Black 20th Red/Green 33rd Blue/Wht/Org 46th Red/Wht/Blue
8th Red/Black 21st Orange/Green 34th Blk/Wht/Org 47th Grn/Orn/Red
9th Green/Black 22nd Blk/Wht/Red 35th Wht/Red/Org 48th Org/Red/Blue
10th Orange/Black 23rd Wht/Blk/Red 36th Org/Wht/Blue 49th Blue/Red/Org
11th Blue/Black 24th Red/Blk/Wht 37th Wht/Red/Blue 50th Blk/Org/Red
12th Black/White 25th Grn/Blk/Wht 38th Blk/Wht/Grn
13th Red/White 26th Org/Blk/Wht 39th Wht/Blk/Grn
Courtesy Belden