Rack PDU Selection & Buying Guide

​​Introduction

Selecting the right rack PDU is about more than just supplying power. The choices you make at this stage can affect rack layout, monitoring capability, scalability, and long-term operational efficiency.

This guide is designed to help you navigate the key considerations when choosing a rack PDU — from physical fit and power architecture through to monitoring and outlet configuration — so you can specify a solution that works today and adapts as your infrastructure evolves.

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1. Start With the Rack, Not the PDU

Before looking at power features, it’s important to understand the physical constraints of the rack itself.​​

Key considerations include:

• Rack height (e.g. 42U, 45U)

• Vertical vs horizontal PDU mounting

• Front or rear mounting position

• Available mounting space alongside cable managers and airflow components

Vertical PDUs are commonly used in modern racks to maximise usable U-space, while horizontal PDUs may suit smaller enclosures or edge deployments.​

Choosing the correct form factor early avoids compromises later.

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2. Power Architecture: Single Phase vs Three Phase

One of the most fundamental decisions is whether a single-phase or three-phase PDU is required.

Single-phase PDUs are typically used where loads are modest, rack density is low, or power availability is limited.

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Three-phase PDUs are often preferred in higher-density racks where:

• Power needs are growing

• Load balancing is important

• Infrastructure efficiency is a priority

The choice affects usable capacity, redundancy strategies, and future scalability.

Understanding your upstream power availability is key before locking in a PDU type.

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3. Load Planning & Headroom

Accurate load planning helps prevent nuisance trips, uneven loading, and early replacement.

When estimating rack load, consider:

• Current equipment draw

• Planned growth

• Diversity and peak loads

• Sensible headroom

A common mistake is assuming the supply rating equals usable capacity. In practice, allowing margin for growth and operational flexibility leads to more reliable outcomes.

For complex environments, even a simple load calculation can provide valuable clarity before specifying hardware.

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4. Outlet Configuration & Density

Outlet choice impacts far more than simple compatibility.

Key factors include:

• Outlet type (e.g. IEC C13, C19)

• Quantity and spacing

• Orientation (straight vs angled)

• Front- or rear-facing outlets

Mixed outlet configurations can support a wider range of equipment, while thoughtful spacing reduces cable congestion and improves airflow.

Outlet layout is also one of the most common drivers for custom PDUs, particularly where rack layouts are non-standard.

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5. PDU Types Explained: Basic, Managed, Intelligent

Rack PDUs are typically grouped into three categories based on functionality.

Comparison Table:

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