Okonite wire and cable - Short Circuit Currents - Shielding Currents
Short Circuit Currents
Shielding Currents

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Shield short circuit current formula

For short-circuit shield ampacity with a known cable shield area (or an area that can be calculated from formulas given below), the following simplified formula may be used.

I= [ sq root (N / K) / A ]

..........

  Where  I = Amperes
A = Shield Area in CM
N = Number of Cycles
T1 = Initial Temp. 65C
K = See Table Below

 

T2 MAX
C

VALUES OF K

Cu

Al

Pb

150
200
250
350

0.193
0.288
0.372
0.517

0.083
0.123
0.159
0.221

0.0063
0.0094
0.0121

NOTE: Use 200 for thermoplastic and 350 for thermosetting jackets.

  • For Overlapped Tape (1) A = 4bdm x square root [ 2 (W-L)  /  W ]

  • For Tubular Sheath A = 4bdm

  • For Wire Braid A = Nds2

  • For Spaced Tape A = 1.273 Wb

  • Where:

 

b = Shield thickness, mils

...........

W = tape width, mils

dm = mean diameter, mils

A = area in CM

ds = wire diameter, mils

L = lap of tape, mils

N = number of wires

(1) Substituting various overlap values gives the following:

OVERLAP .......... AREA
1/2 W (50% 4bdm
1/4 W (25%) 3.27bdm
1/5 W (20%) 3.16bdm
1/8 W (12.5%) 3.02bdm

 

Permissible short circuit currents
for copper shielding tape* amperes

Shield
Diam.
Inches

Effective
Shield Area
Circular
Mils

Short Circuit Time in
Number of Cycles (60 per sec.)

1

2

4

8

16

30

60

1/2...
3/4
...
1
...
1 1/4
...
1 1/2
...
1 3/4
...
2
...
2 1/4
...
2 1/2
...
2 3/4
...
3
..

7,484......
11,264
......
15,044
......
18,824
......
22,604
......
26,384
......
30,164
......
33.944
......
37.724
......
41,504
......
45,284
......

4,016
6,044
8,073
10,101
12,130
14,158
16,187
18,215
20,243
22,272
24,300

2,840
4,274
5,708
7,143
8,577
10,011
11,446
12,880
14,314
15,749
17,183

2,008
3,022
4,036
5,051
6,065
7,079
8,093
9,107
10,122
11,136
12,150

1,420
2,137
2,854
3,571
4,289
5,006
5,723
6,440
7,157
7,874
8,591

1,004
1,511
2,018
2,525
3,032
3,540
4,047
4,554
5,061
5,568
6,075

733
1,104
1,474
1,844
2,215
2,585
2,955
3,.326
3,696
4,066
4,437

518
780
1,042
1,304
1,566
1,828
2,090
2,352
2,613
2,875
3,137

*Values are derived from the Conductor Currents formula and T2 = 200C, T1 = 65C, 5 mil copper tape with 12.5% overlap.

 


ENGINEERING TECHNICAL CENTER

Every effort has been made to ensure the accuracy of this presentation.
However, information is subject to change. Not responsible for typographical errors.

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102 Hilltop Road
Ramsey, New Jersey 07446
Phone 201-825-0300
Fax 201-825-3524
info@okonite.com

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