Conduit Size And Fill; Electric Motors - Honeywell AUTOMATIC CONTROL Engineering Manual

CONDUIT SIZE AND FILL

The fill factor for nonlead covered conductors is 53 percent
for one conductor, 31 percent for two conductors, and 40 percent
for three or more conductors. Table 21 shows internal
dimensions of electrical conduit.
Use the following formula and Tables 21 and 22 to determine
correct conduit size:
A C = (NA W1 + NA W2 + NA W3 + ... + NA WN ) ÷ F
Where:
A C = Conduit internal cross-sectional area, in
square inches.
N = Number of conductors of given cross-
sectional area.
A W = Cross-sectional area of a given conductor
including insulation, in square inches (see
Table 22).
F = Fill factor, in decimals.
Where:
Cross-sectional area of
No. 18 TFN conductor
Cross-sectional area of
No. 16 TFN conductor
Fill factor
Motor Type
Universal Armature and field connected in series. Operates on dc or
(Series) ac with approximately the same speed and torque.
Split-Phase Uses a pair of field windings for starting with one winding
Starting slightly lagging. One winding is disconnected by a
centrifugal switch when running speed is reached.
Capacitor Same as split-phase with a capacitor connected to the
Starting winding that stays on line. Provides greater starting torque
with high efficiency and power factor.
Shaded-Pole A short-circuited winding is used on each pole piece along
Starting with a normal winding. Magnetic flux in the shorted turn
produces starting torque. Torque is low.
Repulsion Operates as a repulsion motor on starting and a centrifugal
Starting switch converts it to an induction motor when running speed
is reached. Motor has a commutator as in a dc motor.
Provides high starting torque.
2
= 0.0062 in
2
= 0.0079 in
= 40 percent
Table 23. Single-Phase Motor Characteristics and Applications.
Characteristics
Then:
A C = [(8 x 0.0062) + (14 x 0.0079)] ÷ 0.4
A C = 0.4005 in 2
From Table 21, a 3/4-in. rigid (0.533 in
2
(0.518 in ) is required for the conduit run.
If only the diameter (dia) is available:
The cross-sectional area in in
NOTE: It is obvious from Table 22 that conduit size for a given
mix of conductors can vary depending upon the type
of insulation used.

ELECTRIC MOTORS

Single-phase electric motors are classified by the method used
to start the motor. Table 23 describes the characteristics and
typical applications of single-phase motors by classification.
No special means of starting is required for three-phase motors,
since starting (rotational) torque is inherent in three-phase
motors. A three-phase motor can be reversed by switching any
two phases.
Where either ac or dc may be available. Used for
portable tools, vacuum cleaners, electric
typewriters, etc.
Where starting torque and varying load are not
excessive. Used for oil burners, washing
machines, grinding wheels, etc.
Where high starting torque and heavy varying
loads exist. Used for air conditioners,
refrigerators, air compressors, etc.
Where starting torque is low and less than 1/20
horsepower is required. Used for electric clocks.
Where high starting torque is required. Used in
machine shops.
485 ENGINEERING MANUAL OF AUTOMATIC CONTROL
GENERAL ENGINEERING DATA
2
) or flexible conduit
2
= π(dia ÷ 2)
Application
2
.