Juniper MX240 Hardware Manual page 246

WARNING:
from the DC circuit. To ensure that all power is off, locate the circuit breaker on the
panel board that services the DC circuit, switch the circuit breaker to the off position,
and tape the switch handle of the circuit breaker in the off position.
You connect DC power to the router by attaching power cables from the external DC power sources to
the terminal studs on the power supply faceplates. You must provide the power cables (the cable lugs are
supplied with the router). For power cable specifications, see
MX240 Router" on page
To connect the DC source power cables to the router for each power supply:
1. Switch off the dedicated customer site circuit breakers. Ensure that the voltage across the DC power
source cable leads is 0 V and that there is no chance that the cable leads might become active during
installation.
2. Wrap and fasten one end of the ESD grounding strap around your bare wrist, and connect the other
end of the strap to the ESD point on the chassis.
3. Switch the DC circuit breaker on the power supply faceplate to the off (0) position.
4. Remove the clear plastic cover protecting the terminal studs on the faceplate.
5. 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 RTNDC cables to chassis
ground:
The cable with very large resistance (indicating an open circuit) to chassis ground is –48V.
The cable with very low resistance (indicating a closed circuit) to chassis ground is RTN.
CAUTION:
polarity. The power source cables might be labeled (+) and (–) to indicate their
polarity. There is no standard color coding for DC power cables. The color coding
used by the external DC power source at your site determines the color coding
for the leads on the power cables that attach to the terminal studs on each
power supply.
Before performing DC power procedures, ensure that power is removed
65.
You must ensure that power connections maintain the proper
"DC Power Cable Specifications for the
249