 |
 |
 |
| Based on 2 g.p.m. @ 1000 F temperature rise, maximum temperature 1670 F. OHM’s per foot cable - both lead |
|
300
|
400
|
500
|
600
|
650
|
800
|
|
|
Resistance
(R) oer foot
|
.0000836
|
.0000625
|
.0000502
|
.0000422
|
.0000388
|
.0000312
|
|
Impedance
(Z) per foot
|
.0000935
|
.0000855
|
.0000650
|
.0000581
|
.0000524
|
.0000470
|
|
Length
MCM
|
AMPERES
CONTINUOUS DUTY CURRENT
|
|||||
|
300
|
400
|
500
|
600
|
650
|
800
|
|
|
3ft
|
10720.
|
12400.
|
13700.
|
15200.
|
15800.
|
17620.
|
|
4ft
|
9300.
|
10890.
|
12000.
|
13100.
|
13550.
|
15220.
|
|
5ft
|
8350.
|
9700.
|
11400.
|
11570.
|
12200.
|
13420.
|
|
6ft
|
7660.
|
8800.
|
9800.
|
10800.
|
11100.
|
12480.
|
|
7ft
|
7060.
|
8100.
|
9100.
|
9900.
|
10300.
|
11550.
|
|
8ft
|
6600.
|
7700.
|
8500.
|
9100.
|
9680.
|
10720.
|
|
9ft
|
6210.
|
7100.
|
8000.
|
8700.
|
9160.
|
10400.
|
|
10ft
|
5900.
|
6800.
|
7640.
|
8300.
|
8650.
|
9650.
|
|
11ft
|
5560.
|
6500.
|
7250.
|
7920.
|
8250.
|
9100.
|
|
12ft
|
5350.
|
6200.
|
6950.
|
7620.
|
7920.
|
8700
|
|
13ft
|
5160.
|
6000.
|
6650.
|
7300.
|
7600.
|
8400.
|
|
14ft
|
5000.
|
5750.
|
6420.
|
7000.
|
7300.
|
8130.
|
|
15ft
|
4800.
|
5570.
|
6200.
|
6800.
|
7100.
|
7780.
|
|
16ft
|
4650.
|
5400.
|
6000.
|
6560.
|
6820.
|
7620.
|
|
17ft
|
4500.
|
5150.
|
5850.
|
6360.
|
6640.
|
7400.
|
|
18ft
|
4420.
|
5050.
|
5670.
|
6100.
|
6460
|
7100.
|
|
19ft
|
4300.
|
4950.
|
5540.
|
6000.
|
6270.
|
7000.
|
|
20ft
|
4220.
|
4850.
|
5380.
|
5840.
|
6110.
|
6820.
|
|
Duty
Cycle
|
Multiplier
|
|
100%
|
1.00
|
|
90%
|
.95
|
|
80%
|
.90
|
|
70%
|
.84
|
|
60%
|
.78
|
|
50%
|
.71
|
|
40%
|
.63
|
|
30%
|
.55
|
|
20%
|
.45
|
|
10%
|
.32
|
|
5%
|
.22
|
|
3%
|
.17
|
|
2%
|
.14
|
DETERMINING THE PROPER MCM RATING |
CABLE SELECTION CHART - MCM |
| To determine the proper MCM rating, it is first necessary to know (a) the duty cycle, (b) current to be used and (c) length of the cable to be used. |
| Once this has been determined, proceed as follows, assuming the duty cycle has been set at 20%, the current at 20,000 amperes and the cable length at 7 feet : |
|
(1) Consult the multiplier chart, uppet left, and at the 20% duty cycle line you find the multiplier of .45 (2) Multiply the current required, 20,000 amperes, by .45 and you have the continuour duty current of the cable, 9,000 amperes. (3) Refer to the MCM rating chart, upper right, and find the cable length, 7 feet. Looking acrose this 7 foot line, find the figure nearest to the continuous duty current of 90,000 amperes, in this case 9,100. The top of this column then shows a 500MCM cable is required. |
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