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|  MIL-S-17000N(SH)
3.6.23.4 Buses for each voltage and frequency shall be isolated from all
other buses, either by limiting the number of buses to one per switchboard unit
or by effecting the maximum practicable separation between multiple buses within
a single switchboard unit.
3.6.23.5 Phase rotation and polarity. For a.c., like phases shall be
similarly disposed, that is, facing the front of the switchboard or panel, the
phase rotation shall be A, B, and C, respectively, from right to left, top to
bottom or front to back. For d.c., polarity shall be positive (+), negative (-)
from right to left, top to bottom and front to back. Consideration will be
given to other arrangements, where they afford copper reduction, improved
--
electrical clearances, or space saving. This requirement applies particularly
to bus bars and fuses.
3.6.23.6 Casualty power connection. Provision shall be made on 450 V,
60 Hz buses for connection of a type TSGA-60 cable for casualty power feed.
Cable, connectors, and casualty power terminal shall be furnished by the
installing activity.
3.6.23.7 Current rating. The current carrying capacity of the bus bars
shall be based upon 75 percent of the continuous rating of all connected switches
including additional switches. The size of the bus bars shall be selected on a
basis of the current-carrying ratings shown in table IV and shall be kept to a
minimum as far as practicable. In no case shall the copper be smaller for a
given current than the corresponding sizes listed in table IV. The ratings shown
are based on a 95F rise above a 122F ambient and on the separation or arrange-
ment of phases sufficient to neglect mutual inductance between phases and inter-
ference with radiation of neighboring conductors. If the spacing is not large
enough to neglect inductance between phases or interference in radiation, an
appropriate reduction in the current ratings given in table IV shall be made.
TABLE IV.
Ampere rating of rectangular bus bars placed on edge.
D.c. ampere
Size of bars
A.c. ampere
Cross sectional
rating
rating
area
(inches)
(in2)
210
210
0.094
3/4
X
1/8
285
285
.125
1
X
1/8
425
425
.188
1-1/2
X
1/8
.250
555
555
2
X
1/8
265
.140
3/4
X
3/16
265
355
355
.188
1
X
3/16
.278
550
550
1-1/2
X
3/16
710
700
.375
2
X
3/16
295
295
.188
3/4
x
l/4
2.50
410
410
1
x
1/4
600
.375
600
1-1/2
x
1/4
800
780
.500
2
x
1/4
1,050
1,000
.625
2-1/2
x
1/4
35
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