Load balancing in IBM switched and monitored Power Distribution Units (PDUs) - IBM Systems

Resolving The Problem

Source

RETAIN tip: H207648

Symptom

The internal circuits of some Power Distribution Units (PDUs) could be overloaded if users are not aware of the circuit breaker specifications and how the PDU outlets are connected.

If loads are greater than the specification of the circuit breaker, it will trip and turn off the load.

Affected Configurations

The system is configured with one or more of the following IBM options:

• IBM 1U 12 C13 Switched and Monitored 60A/208 V/3 Phase PDU, option 46M4005, replacement part number 46M4017
• IBM 1U 12 C13 Switched and Monitored DPI PDU, option 46M4004, replacement part number 46M4016
• IBM 1U 9 C19/3 C13 Switched and Monitored 60A/208 V/3 Phase PDU, option 46M4003, any replacement part number
• IBM 1U 9 C19/3 C13 Switched and Monitored DPI PDU, option 46M4002, any replacement part number

This tip is not system specific.

This tip is not software specific.

Workaround

The IBM switched and monitored PDUs have either six or nine circuit breakers on the front of the PDU. Each circuit breaker is rated for 20 amps of current. When connecting loads, ensure that the rating for each circuit breaker is not exceeded.

Some of the PDUs can be connected to three-phase power. The loads should be distributed across all three phases. If single-phase power is used, it is also wise to distribute the load between the outlet groups.

The PDU models with twelve C13 outlets on the front have Phase 1 connected to the first four outlets, outlet group one. Phase 2 is connected to the next four outlets, outlet group two, and Phase 3 is connected to the last four outlets, outlet group three.

The PDU models with nine C19 outlets on the front have Phase 1 connected to the first three outlets, outlet group one. Phase 2 is connected to the next three outlets, outlet group two. Phase 3 is connected to the last three outlets, outlet group three.

Some models have three outlets on the rear of the PDU. These outlets are not monitored or switched. They are each connected to different phases.

To balance loads on the PDU, do not plug in loads so that there is more load on one group of outlets than the others. For example, if there are three loads on a nine-outlet PDU, do not use outlets 1, 2, and 3. Instead, use outlets 1, 4, and 7.

If there are three loads on a twelve-outlet PDU, use outlets 1, 5, and 9. If there are more then three loads, distribute them across the three output groups.