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T4000 Power System Description


Power Supply Slots

The T4000 router has two redundant, load-sharing power supplies, located at the lower rear of the chassis in slots PEM0 and PEM1 (top to bottom). Power supplies are hot-removable and hot-insertable.

Power Supply Function

The power supplies connect to the midplane, which distributes the different output voltages produced by the power supplies to the T4000 router components, depending on their voltage requirements.

Supported Power Supplies

The T4000 router supports the power supply in Table 1.

Table 1: Supported Power Supplies


Model Number

First Supported Junos OS Release

Six-input DC power supply



Power Supply Components

Each six-input DC power supply weighs approximately 39.7 lb (18.0 kg) and consists of six inputs, two blowers, a front and side air filter, and LEDs to monitor the status of the power supply. Each power supply is cooled by its own internal cooling system. Figure 1 shows the six-input DC power supply.

The six-input DC power supply inputs are labeled INPUT 0, INPUT 1, INPUT 2, INPUT 3, INPUT 4, and INPUT 5, from top to bottom. Each 60 A input consists of –48 VDC and return.


There are no circuit breakers or passive fuses in the router.

Figure 1: DC Power Supply
DC Power Supply

Table 2 describes which components are powered by each input.

Table 2: Components Powered by Each Six-Input DC Power Supply Input




Fan trays

INPUT 1 through INPUT 5

FPCs, Routing Engines, control boards, SIBs, craft interface, SCGs, and other components in the router.


When the T4000 router is operating normally and both power supplies are switched on, load sharing between them occurs automatically. When one power supply fails or is turned off, the other power supply immediately assumes the entire electrical load for the system. A single power supply can provide full power for as long as the router is operational. For power management of the T4000 router, see T4000 Power Management (Three 80-A Cables on a Six-Input DC Power Supply) and T4000 Power Management (Four 60-A Cables on a Six-Input DC Power Supply).