Power conductors 69
Table 21
Maximum allowable voltage drops
I
Conductor From To V drop
-
BAT
Pedestal Dist. DisChg 1.0
+ BR Pedestal
Dist. Corn
1.0
-BAT
Dist. (-
) Battery term
0.25
+BR
Dist. (+) Battery term 0.25
-BAT
Rectifier Disk
Chg
0.5
+ BR Rectifier Dist. Corn 0.5
Mote 7: Dist. is an abbreviation for Battery Distribution Box (i.e. QBL15, CtBLl2).
CAUTION
Although 0.25/0.5/1.0 volts is the maximum drop allowed, the
insulation and temperature rating vs current will often dictate a wire
size that will create smaller voltage drops on short lengths. After
using the formula, consult wire tables to ensure that the temperature
rise is acceptable.
-
Examples
The following three examples show how to make wire size calculations.
1. A Bat or BR conductor from the
QBLl5
to a pedestal is 18 feet long and
must carry a maximum of 36 Amps:
Using CM=
11.1x
Ix D/V
CM = 11.1 x 36 x 18/0.5 = 14385.6
Choosing a standard gauge equal to or larger than this will mean 8 AWG
which has a cross section of 16510 CM.
Up to 40 amps is allowable with 8 AWG even when the insulation is rated
only 20 degrees C above the expected maximum ambient temperature.
Power engineering 553-3001-l 52