PDU Buying Guide

How to buy the right power distribution unit for an IT server rack or network closet.

This buying guide will help you:

• Understand what a PDU is and recognize its key features
• Know the key questions to ask before selecting a PDU
• Compare the different types of PDUs available
• Learn about the important PDU features
• Find the right PDU for your application

What is a Power Distribution Unit (PDU)?

A Power Distribution Unit (PDU) is a device with multiple outlets designed to distribute power to computers, servers, network switches and other it devices in a rack. PDUs come in a variety of styles that provide everything from basic power distribution to enhanced remote power management.

How to Choose a PDU for Your Network or Data Center

These are the top 6 factors to consider in your buying decision:

1. Horizontal vs. Vertical Installation

PDUs can be mounted horizontally or vertically inside or outside the rack enclosure:

Horizontal PDUs are installed in the rack and take up one or two rack spaces (1U-2U). Because of their smaller size, horizontal PDUs have fewer outlets.

Vertical PDUs can be mounted on the back or side of the rack enclosure. Deep racks will often leave space for vertical PDUs to be mounted inside the enclosure. Vertical PDUs can have up to 40 outlets.

2. Voltage of Your Connected Equipment

In North America, the voltage used to power servers and networking equipment is typically 120V or 208/240V.

Europe and Asia typically provide 230V power.

Be sure that the PDU input plug matches the receptacles of your input power source.

3. Outlet Types

The PDUs outlets should match the plugs on the equipment you'll be connecting. Some PDUs offer a mix of outlet types.

Common PDU Outlet Types

NEMA 5-15R	NEMA 5-20R	IEC-320-C13	IEC-320-C19
NEMA L5-20R	NEMA L5-30R	NEMA L6-20R	NEMA L6-30R

4. Number of Outlets

Select a PDU with more outlets than the number you need to ensure room for future rack growth.

5. Maximum Output Capacity

The total power required by equipment connected to the PDU must not exceed the PDU's maximum load rating (expressed in kVA). In North America, the maximum input and output capacity is limited to 80% (this is referred to as “agency de-rating”). For example, a single-phase PDU with a nominal voltage of 120V and de-rated input current of 12A (80% of 15A), has a load capacity of 1.44 kVA (120V x 12A).

6. Special Features

Remote management software – Tripp Lite's PowerAlert® Device Manager (PADM) is the firmware that enables remote management of PDUs equipped with an LX network interface card. The latest version, PowerAlert Device Manager 20.0 (also known as PADM20), provides customizable and intuitive remote management capabilities, expanded maintenance functions and backup and restoration of device configurations. Learn more about PowerAlert.

Automatic device reboots - Tripp Lite PDUs equipped with an LX network interface card include an Auto-Probe feature that automatically detects and fixes network connectivity problems, helping you avoid costly truck rolls for simple reboots. For example, a PDU can be configured to ping a router over the network. If the router fails to respond, the PDU with automatically power cycle the router. Learn more about Auto-Probe.

Environmental monitoring - A monitored or switched PDU's network interface can be used to receive information from environmental sensors connected to the PDU. The sensors monitor ambient temperature and humidity, as well as contact closure status of alarm, security and telecom products. See Tripp Lite's environmental sensor accessories.

Types of PDUs Available

Basic PDUs
A basic PDU provides reliable AC power distribution to multiple devices from a UPS system, generator or utility power source. See Tripp Lite's selection of Basic PDUs.

Local Metered PDUs
Local metered PDUs have digital load ammeters to enable local current monitoring, helping IT managers balance loads and prevent overloads. Select models also include premium Isobar® surge protection. See Metered PDUs available from Tripp Lite.

Monitored PDUs
Monitored PDUs include the features of Local Metered PDUs, plus a network interface to support remote monitoring and control from virtually any location. Explore Tripp Lite's selection of Monitored PDUs.

Switched PDUs
Switched PDUs Include all Monitored PDU features, plus local or remote control of individual outlets. A Switched PDU helps the IT administrator eliminate costly site visits with the ability to remotely reboot malfunctioning devices and turn power off and on to each outlet See Tripp Lite's selection of Switched PDUs.

Auto Transfer Switch (ATS) PDUs
An ATS PDU provides a redundant power option for single-corded network devices. If the primary source becomes unstable or fails, the ATS switches over to the secondary power source until the primary input is restored. Explore Tripp Lite's ATS PDUs.

Hot-Swap PDUs
Hot-Swap PDUs include dual AC inputs and a manual transfer switch that allows maintenance, repair or replacement of compatible UPS systems without interrupting power to connected equipment. See Hot-Swap PDUs from Tripp Lite.

Network Switch/PDU Combo Units
These units combine a managed or unmanaged Gigabit Ethernet switch with a network-grade PDU. The switch/PDU uses just 1U of rack space and is perfect for distributed networks where space is at a premium. Select models include Power over Ethernet (PoE) capabilities. See Tripp Lite's Gigabit Ethernet Switches with Built-in PDUs.

What Type of PDU Do You Need?

Below is a PDU features and benefits chart that compares features and benefits to help you determine which PDU is best for your application.

PDU Features Overview

Horizontal or vertical form factors

• PDUs can have either a horizontal design or a vertical design.
• Horizontal PDUs mount in a rack, occupying 1U or 2U (rack units) of space. Mounting ears are reversible for front- or rear-facing rack-mount installation.
• Vertical PDUs mount on the back or sides of the rack's posts, occupying 0U of space. This design allows for up to 48 outlets on a single PDU.
• Tripp Lite's vertical PDUs enable simple toolless mounting into compatible racks for hassle-free installation.

Digital load metering

• A front-panel digital load meter on Local Metered PDU models displays total PDU output current in amps for local monitoring of connected loads.
• If the outlets are grouped in different load banks, each load bank has a dedicated meter.
• Monitoring total PDU output helps prevent PDU and supply circuit overloads that can cause costly downtime.

Triple load meters

Remote monitoring

• Select PDUs feature a built-in LX Platform network management card that provides enhanced remote management capabilities.
• The Java-free HTML5-based LX Platform network interface and software included with Tripp Lite's Monitored PDUs can send automated email notifications that help IT managers prevent accidental overloads, power loss and downtime from virtually anywhere.
• The network interface can be used to monitor information received from standard sensors about a wide variety of functions. For example, you can monitor door-closure detectors, smoke alarms, temperature/humidity sensors and other devices, receiving alerts and logging operational data automatically.

Individual outlet control

• Switched PDUs provide advanced network control and remote power monitoring, including the ability to turn on, turn off, reboot or lock out power to individual outlets.
• Individual outlet control is a valuable feature that reduces the frequency of on-site visits, savings expenses and reducing downtime, thus lowering the PDU's total cost of ownership. Switched PDUs are ideal for branch offices and retail stores with no on-site IT staff.
• A Switched PDU is valuable for network applications that require automated load shedding or defined power-on sequences to avoid inrush overloads.
• Outlet LEDs help local IT managers determine at a glance which outlets are live at that moment.

Power Measurement Features

• Shared data centers, such as colocation facilities, require accurate accounting of a client's total electricity consumption. A PDU that measures real-time load/current data with billing-grade accuracy of +/- 1% ensures energy costs are invoiced correctly.
• Cryptocurrency miners and others creating non-fungible tokens (NFTs) also require accurate measurement of power consumption to control power costs and maintain accurate accounting of profitability.

Circuit breakers

• Most PDUs include one or more circuit breakers to protect against dangerous overloads and short circuits.

Auto transfer switching

• PDUs with auto transfer switching provide redundant power to devices that do not have redundant power supplies, either by necessity or as a strategy to reduce hardware, power and cooling costs.
• Separate primary and secondary input cords connect to two different compatible power sources. If the primary source becomes unstable or fails, the ATS switches over to the secondary power source until the primary input is restored and stable.

Hot-swap capability

• Keeping mission-critical data center equipment operating at its optimal level requires periodic maintenance. Hot-swappable PDUs work in conjunction with your UPS system to keep everything running 24/7/365.
• These PDUs have a manual transfer switch that enables you to manually control the PDU's input power source for maintenance or equipment replacement with no interruption of performance.
• For further reading on hot-swappable PDUs, refer to our hot-swap technology page.

Automatic device reboot capability

• Tripp Lite PDUs with an LX network interface card include Auto-Probe, a feature that automatically detects and fixes network connectivity problems, helping you avoid the time and costs of a site visit for simple reboots.
• With Auto-Probe, a PDU can, for example, be configured to ping a router at regular intervals. If the router fails to respond, the PDU will automatically power cycle the router to restore connectivity.

Convenience and durability features

• Mounting Options – Detachable mounting brackets support rack, surface or under-table mounting. When choosing a horizontal PDU, consider a reversible housing so outlets can be configured at the front or the back of your rack to suit your needs. If you are buying a vertical PDU, look for toolless mounting that snaps into compatible racks.
• Cords – Look for a PDU with a longer cord if you need flexibility of placement or if your source outlet is not close by. Tripp Lite's selection includes models with cords up to 15 ft. in length. A heavy-duty cord ensures the PDU will handle heavy current loads from multiple devices.
• Cord Retention Brackets – Most Tripp Lite PDU models include detachable brackets with built-in anchor points to secure equipment power cords, helping to prevent accidental disconnections.
• Metal Housing – A metal case increases the PDU's operational service life, a must for demanding environments.

Frequently Asked Questions

What is the difference between a UPS and a PDU?
An Uninterruptible Power Supply (UPS) provides battery backup to IT equipment and other electronics during power outages. A UPS also filters incoming power and provides surge protection.

A Power Distribution Unit (PDU) distributes the power from the UPS or other AC source, such as a wall outlet or generator, to multiple devices. It does not generate or condition power on its own.

What is the best power supply for a rack?
A Power Distribution Unit (PDU) is designed for the specific purpose of powering multiple devices in a server rack or enclosure. A PDU distributes the available amperage evenly and efficiently among all outlets so that all connected servers, networking hardware, telecom equipment and other devices receive the best available power to maintain operation. PDUs are available in a variety of styles that provide everything from basic power distribution to enhanced remote power management.

What is the difference between a PDU and a rack-mount power strip or surge protector?
PDUs, power strips and surge protectors all provide multiple outlets. What a PDU adds is support for robust distribution of reliable network power for multiple servers, networking hardware, telecom equipment and other IT devices. A PDU will distribute the available amperage evenly and efficiently among all outlets so that all connected equipment receives the best available power to maintain operation. PDUs can also provide higher maximum load capacities than power strips. Basic 120V PDUs are available from Tripp Lite that can provide up to 3.8kW of power, much more than even the typical industrial power strip can handle.

Depending the type of PDU, you also get options for input current monitoring, remote monitoring and control, secure access and environmental monitoring.

Note that most PDUs do not provide surge protection because a PDU installed in a rack is typically connected to a UPS system. The UPS protects connected equipment from power surges and line noise interference. For Tripp Lite PDUs with premium Isobar® surge protection built in, see our selection.

What is the difference between a power distribution unit and a power distribution center or cabinet?
A power distribution cabinet, also known as a power distribution center, is electrical equipment that provides supply and redistribution of electrical energy, protection of electrical power lines and protection of the overload and short circuit currents. See Tripp Lite solutions for power distribution centers.

How do you use a hot-swap PDU?
The dual input and manual bypass features of the PDU enable UPS system maintenance–from battery replacement to complete power module exchange–without powering down connected mission-critical equipment and hiring costly service specialists. Here are the basics of using a hot-swap PDU:

1. Plug the primary input of the hot-swap PDU into an on-line UPS system.
2. Plug the secondary input into utility power, i.e. a wall outlet.
3. If the UPS needs to be taken offline for maintenance, repair or replacement, use the manual transfer switch to move the connected load to the secondary input. When the UPS is restored, switch the PDU back to the primary input.

For further reading, refer to our hot-swap technology page.

How does a PDU help monitor conditions in the rack, network closet or data center?
A monitored or switched PDU has a network interface that can be used to receive information communicated from environmental sensors connected to the PDU, helping personnel ensure optimum operating conditions. The sensors monitor ambient temperature and humidity, as well as contact closure status of alarm, security and telecom products.

Learn more about Tripp Lite's solutions for environmental monitoring.

Must-have accessories: PDU power cords
Each device you plug in must have at least one power cord connecting it to the PDU. You could use the cord that came with the device, but consider these options that help you manage your devices more efficiently:

• Color-coded power cords – Look inside the average data center rack and you'll likely see a confusing array of gray or black cords. By color-coding the power cords running to different types of equipment, the right cord is easy to identify at a glance and will help prevent accidental disconnection of the wrong device. Tripp Lite offers an array of PDU cords in blue, green, orange, red, white and yellow – along with gray and black, of course. See the selection.
• Cords of different lengths – Devices mounted close to the PDU need only a short cord. Those mounted furthest from the PDU may require a cord that is several feet long. Using the appropriate-length cord helps reduce cable clutter and promotes more efficient airflow and cooling within the rack. See Tripp Lite's full selection of power cords.
• Plug-lock inserts – Help prevent accidental disconnection of critical equipment. Plug-lock inserts strengthen the physical connection of the cord and outlet and provide a no-clutter alternative to zip-tie cords or electrical tape. See plug-lock inserts now.
• Power cord adapters – If you find you need different types of receptacles than your PDU provides, power cord plug adapters are a simple and inexpensive solution that enables you to keep using your existing PDU. Find an adapter cord now.