9. Verify that the DC power cables are correctly labeled before making connections to the power supply.
In a typical power distribution scheme where the return is connected to chassis ground at the battery
plant, you can use a multimeter to verify the resistance of the –48V and RTN DC cables to chassis
ground:
•
The cable with very high resistance (indicating an open circuit) to chassis ground is negative (–) and
will be installed on the –48V (input) DC power input terminal.
•
The cable with very low resistance (indicating a closed circuit) to chassis ground is positive (+) and
will be installed on the RTN (return) DC power input terminal.
CAUTION: You must ensure that power connections maintain the proper polarity.
The power source cables might be labeled (+) and (–) to indicate their polarity. There
is no standard color coding for DC power cables.
10. Install each power cable lug on the DC power input terminal, securing it with the nut (see
Figure 164 on page 302). Apply between 24 in.-lb (2.7 Nm) and 25 in.-lb (2.8 Nm) of torque to each nut.
(Use the 13/32 in. [10 mm] nut driver or socket wrench.)
a. Secure each positive (+) DC source power cable lug to the RTN (return) DC power input terminal.
b. Secure each negative (–) DC source power cable lug to the –48V (input) DC power input terminal.
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