Designing a better power distribution unit (PDU)

written by John Day December 14, 2016

Legacy PDU manufacturers do not support the mission-critical power needs required by today’s facility managers. Their stagnant design continues to promote an inherent and unnecessary danger to PDU maintenance workers. Many of these legacy devices continue to trade innovation for low-cost production -- at the expense of safety.  To ensure that you are investing in the best of breed PDU products, facility managers and engineers need to add a series of questions to their PDU evaluations to avoid dangerous consequences.
These questions include:

• Is it possible to safely work on an energized PDU, even with proper PPE?
• Can you safely add loads while the unit is under power?
• Is there proper component separation and isolation in the PDU?
• Is the PDU metering proprietary or off the shelf?
• If proprietary, can it be easily upgraded, customized or replaced in the field?
• Are thermal magnetic breakers offered and will they trip if the ambient temperature is raised in the data center?
• Will the PDU manufacturer perform custom modifications and designs if requested or when necessary?

One of the main and recurring issues in a legacy PDU is that the direct fault of a distribution breaker could result in cascading faults throughout the entire unit -- causing a complete shutdown of the all the loads that are carried by that PDU. However, if the distribution breaker is properly isolated, the fault could be limited to a single compartment and a single load.
The fact is, next-generation PDU designers are addressing all the aforementioned issues. They realize that safety does not have to come at a high price tag and insightful PDU changes can dramatically improve safety during maintenance procedures. For example, compartmentalization of components is an effective way to provide a safer product.
This simple, but innovative procedure includes the separation of:

• Metering
• Distribution breakers
• Main breakers
• TVSS
• Transformer

By offering this isolation for each component, the risk of personal injury and damage to the other components, are significantly diminished. It cannot be emphasized enough that applying component isolation has many advantages over legacy devices. Facility and plant engineers need to consider the following for each PDU option:

• Metering:

• Legacy manufacturers are offering outdated and proprietary metering not suited for today’s mission-critical facility needs.
• By using readily available and off-the-shelf products, metering can be enhanced without requiring custom mounting arrangements.
• By using a plug-and-play system, products can be configured to provide both isolation and an easy method to replace metering if it fails in the field.
• Main Circuit Breaker:
  • By isolating the main breaker, it increases safety and serviceability.
  • The breaker may be segregated in such a way that it is not exposed to the transformer or any other component.
• Transformer:
  • Transformers should be completely isolated -- all other components can be separated from the other PDU components.
  • Transformers have better thermal characteristics if they are isolated, because there will be no heat transferred to the transformer cabinet from other components.
  • Compartmentalization provides enhanced safety.
• Distribution Breakers
  • Electronic trip to eliminate nuisance tripping due to higher ambient temperature in the data center
  • Isolation for safe serviceability without shut down
  • ISO Compartments for safe connection of future loads without shutdown.
• TVSS & Other Accessories:
  • Isolating components to a single compartment promotes easier service and maintenance procedures.

When considering PDU needs for any facility, plant managers, engineers and facility operators need to consider units with an ISO compartment, capable of safely connecting future loads -- without shutting down the entire PDU.  This innovative design provides for complete isolation of distribution breakers so the load can be connected without shutting down the PDU.
Compromising worker safety for cost-effective PDUs is not a wise business decision. Today's innovative PDU offerings blend innovative engineering that is capable of reducing human error, by protecting facility maintenance personnel from accidental and potentially life threatening injury. You would never consider transporting your family in a vehicle without seat belts or airbags -- why expose your workers to the life-threatening risks inherent within legacy PDU products?
John Day VP of Sales and Marketing at Anord Critical Power, Inc., (ACPI) a recognized leader and innovator in the power distribution market.