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Technical Information

Useful Formulas
The following are standard methods of determining ODs and calculating weights of components that make up a multiconductor cable.

CONDUCTOR
Conductor Weight (lbs./Mft.)
Conductor Formula
Where:
= 3.14
D = Diameter
L = Length
P = Pounds of water/gallon (8.34)
G = Density of copper (8.39), aluminum (2.70)
N = Number of strands
C = Cubic inches of water/gallon (231.0)
K = Weight increase due to stranding
No. of Strands
19
37
49
133 or more
K
1.02
1.026
1.03
1.04

SHIELD
Shield  OD = Diameter under shield + addition (inches)
AWG Size (Braid)
40
38
36
34
32
30
28
Addition
0.14
.018
.022
.028
.035
.044
.056
Shield Weight (Lbs./Mft.)
 Shield Formula
Where:
N = Number of ends per carrier
C = Number of carriers
W = Weight of one shielding strand (Lbs./Mft.)
a = Braid angle
INSUALTION
Insulation Weight (lbs./Mft.)
Insulation Formula
Where:
D = Diameter over insulation (in.)
d = Diamteter over conductor (in.)
K = Constant = 680
G = Specific gravity of insulation

Percent Coverage

Where:
F = NPd/Sin a
N = Number of ends per carrier
P = Picks per inch
d = Diameter of one shielding strand
a = Braid angle
tan a  = 2 (D + 2d) P/C
D = Diameter of cable under shield in inches
C = Number of carriers

TAPE
Tape Weight (lbs./Mft.)
Tape Formula
Where:
K = 1364
t = tape thickness
f = multiplying factor
d = diameter of cable under tape (inches)
G = specific gravity of tape
% Lap
17.5
25
33
50
f
1.25
1.28
1.32
2.0

*AWG Size
40
38
36
34
32
30
d (inches)
.0031
.0040
.0050
.0063
.0080
.0100
W (Lbs./Mft.)
.0291
.0481
.0757
.120
.194
.303

JACKET
Jacket Weight (Lbs./Mft.)
Jacket Formula
Where:
D = Diameter over jacket (inches)
d = Diameter under jacket (inches)
K = 680
G = Specific gravity of jacket material

TWISTING LOSS
Use approximately 3% for all cables OD = diameter of a
single conductor in layer, therefore,
Twisting Loss Formula
or, 25 conductors, each 0.075" OD will fit around a core
diameter of 0.540".
3. Diameter over the outer layer
 = 0.540" + (0.075" x 2)
 = 0.690"


TOTAL WEIGHT (Cabled Conductors)
Weight (Lbs./Mft.) = N x L x W
Where:
N = Number of conductors
W = Weight of one insulated conductor (Lbs./Mft.)
L = Twisting loss (1.03)



AMPACITIES

Assigning a current rating to a wire is really a problem of heat transfer. The watts generated at the conductor must be dissipated through the insulation of the ambient without overheating the conductor or the insulation.

While current ratings for power cables have been officially assigned by such bodies as the Insulated Power Cable Engineers Association and the National Electrical Code, no such ratings have been officially developed for appliance wires or apparatus cables.

Inasmuch as appliance and apparatus designs vary widely, any effort to standardize actual current ratings is just about impossible. The best that can be done is to select a cable insulation that has a thermal rating at least equal to that of the machine and use the nearest NEC rating as a guide for the first approximation of conductor size. If the insulation thermal rating is the same as that of the machine, a current density of the cable equal to that of the machine winding will probably suffice. On the other hand it may be economical to use a cable insulation of higher thermal rating, say 125oC cable in a Class A (105oC) machine. In such a case the cable could be operated at a higher current density than the winding at a savings in both conductor cost and space occupied. Sometimes the space savings will allow thermally upgrading the machine without changing the frame size.

For suggested ampacity ratings, see table below.

Current ratings for different conductor materials may be calculated by multiplying the appropriate copper conductor rating by the following factors:

Nickel-clad Copper ..........0.87
Nickel ...............................0.43

Note: The ultimate temperature an appliance wire reaches is influenced more by its proximity to heat sources (e.g. - resistors, motors, etc.) within the appliance than by the current flowing in the wire itself. The below ratings therefore, should only be used as a guide and in no case should the wire be used in a manner that will cause it to exceed its maximum temperature rating.


 APPLIANCE WIRING MATERIAL
Suggested Ampacities - All Types of Insulation

Size AWG Copper
Temperature
90oC
Copper
Temperature
90oC
Copper
Temperature
90oC
Copper
Temperature
90oC
Copper
Temperature
90oC
Amperes per Conductor
30
28
26
24
22
20
18
16
3
4
5
7
9
12
25
27
3
4
5
7
10
13
20
28
3
5
6
8
11
14
22
30

4
6
7
10
13
17
26
36

4
6
8
11
14
19
29
38
Correction Factors for Various Air Temperatures
30oC
40
50
60
70
80
90
100
125
150
200
1.00
0.91
082
0.71
0.58
0.41
-
-
-
-
-
1.00
0.93
0.85
0.77
0.68
0.57
0.44
0.25
-
-
-
1.00
0.95
0.89
0.83
0.76
0.69
0.61
0.51
-
-
-
1.00
0.97
0.94
0.91
0.87
0.84
0.80
0.77
0.66
0.54
-
1.00
0.98
0.95
0.95
0.91
0.87
0.83
0.80
0.69
0.56
0.43

 
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