4 Power

N+1 Power Configuration

The N+1 power configuration provides DC power redundancy by adding an additional power supply to each DC power grid. The N+1 configuration contains two power distribution units (PDUs): one "system" PDU and one N+1 PDU.

The system PDU distributes AC power from the customer's branch circuit to the three DC power grids, the electronics control module, and the N+1 PDU.

The N+1 PDU provides AC power to an extra 48 VDC load sharing power supply on each of the three DC power grids, plus an extra AC-to-DC converter for the Electronics Control Module. If a single power supply fails, there is still enough DC power available on the failed power supply's corresponding power grid to keep the entire system operational until the power supply can be replaced.

Figure 4-1 N+1 Power Configuration

2N Power Configuration

The 2N power configuration is an optional feature that provides both DC and AC redundancy. The configuration requires a second "system" power distribution unit (PDU) attached to a separate branch circuit. Each system PDU delivers AC power to its own group of load sharing power supplies.

If something within an AC power source fails, the second AC power source supplies power to the entire system except the operator panel if AC1 fails. If a DC power supply fails, there is still enough power available to keep the entire system operational until the power supply can be replaced.

This configuration provides power to the same components as N+1, plus:

• Power for the additional 2N load sharing power supplies (required)

• Power for 2 additional 19-inch racks (1 & 3) each with six outlets

• Power for the redundant AC-to-DC converters for the ECM

Figure 4-2 2N Power Configuration (Optional Feature)

Three-Phase Power - Delta or Wye

Connecting to three-phase power is highly recommended. The single-phase power option requires three circuits for the N+1 configuration and uses six circuits for a 2N power configuration and redundancy. The single-phase power option is provided for customers that do not have access to three-phase power.

There are two 3-phase power options to choose from: Delta or Wye:

Delta:

• Used when the voltage measured from phase-to-phase is 200-240 VAC

• Requires four wires (3-phases plus ground), do not use neutral (a fifth wire)

Wye:

• Used when the voltage measured from phase-to-phase is 380–415 VAC

• Requires five wires (3-phases, ground, and neutral), neutral (N) is required

AC Power Connections

The figure below shows the AC power connections for the SL8500 library.

AC wiring from the power source branch circuit must be installed in conduit (flexible or rigid) with a 90-degree elbow-down fitting. There are six holes provided for the conduit elbows that measure 2.875 cm (1.125 in.) in diameter. The electrician should choose appropriate conduit and fittings for their application that will fit this. The terminal block hole is 6.35 mm (0.250 in.) in diameter, tin plating over brass, and can accommodate up to #6 wire. Wire Range is 6 mm (14 AWG).

In the figure below, AC 1 on the left corresponds to N+1 PDU(standard) and AC2 on the right corresponds to 2N PDU (optional).

Figure 4-3 Delta or Wye

Circuit Breaker Ratings

The minimum circuit breaker ratings required for the service panel are listed in the tables below.

Load Sharing Power Supplies

The DC power grids use load sharing power supplies. Load sharing allows the output voltage of one supply to be monitored and adjusted by other supplies on the bus. In effect, each independent output voltage is adjusted so that all of the independent output voltages are the same to evenly distribute the load. If one output fails or is shorted, it will not bring down the bus.

The two power configurations provide a different number of power supplies for the tape drives and HandBots:

• N+1 allows one power supply for every eight tape drives and one supply for every two HandBots.

• 2N allows one power supply for every four tape drives and one supply for every HandBot.

To order power supplies, see "Power Configurations".