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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.
What is a 0U PDU?
A vertical PDU is also known as a 0U or “zero U” PDU because it takes up no units of rack space. As the name implies, a vertical PDU mounts to the vertical posts in a rack. Standard 19-inch horizontal PDUs can be mounted vertically outside of the rack if extra space is needed for IT equipment.
What is the best PDU for a 42U rack?
A 42U rack is the most common size of floor-standing server rack. Selecting a PDU for a rack of this size depends on how many devices you plan on installing and the devices' power requirements. If your rack will house densely packed 1U servers, make sure you choose a PDU with ample outlet receptacles, plus some open outlets for future growth. Vertically mounted PDUs are available with up to 48 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.
What is the best PDU for an A/V rack?
The best PDU for A/V applications depends on the specific application and setup. For a typical single-location application, such as a conference room that is not in use 24/7, does not require networking and is powered off when not in use, a basic rack-mount PDU like Tripp Lite's PDU1215 will be suitable.
A more complicated A/V system, such as a multi-room system, a digital signage system or a control center, will involve more components and increased demands. Such a system is likely to be operational 24/7/365, will need devices to be monitored and rebooted remotely and will require secured access. An ideal PDU in this case is Tripp Lite's switched PDU model PDUMH15NET.
Types of PDUs Available
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 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 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.
When do you need a switched PDU?
A switched PDU is a must for certain IT applications:
- Branch offices or retail stores without IT staff – Personnel managing IT equipment in branch locations or stores can control and reboot devices without time-consuming and costly site visits.
- Edge computing – Edge deployments may be hundreds or even thousands of miles from the main office. The built-in intelligence of a switched PDU lets IT managers troubleshoot and solve uptime disruptions from any location.
- Difficult-to-access sites – Use a switched PDU to avoid sending IT personnel to far-flung locations, such as cell towers, security camera locations and ATMs, to perform simple reboots.
- Locations not designed for IT equipment – Areas repurposed to hold IT equipment, such as small closets, may not be equipped with or have space for air conditioners or security. A switched PDU's network with environmental sensors connected to the PDU can monitor temperature and humidity, along with the status of security alarms.
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 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.
|Ideal for:||Basic Power Distribution||Local Power Monitoring||Remote Power Monitoring||Remote Power Management||Power Redundancy||Zero Downtime During Maintenance|
Reliable In-rack Power Distribution
Multiple outlets, secure mounting, high quality
Digital Load Meter
Reports power consumption in amps
Enables remote monitoring and control
Programmable or real-time power control
Individually Switched Outlets
Individual programmable or real-time outlet control
Redundant power for non-redundant equipment
Manual Transfer Switch
Enables hot-swap replacement of UPS systems
All Models in this Product Family have this feature
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.
- 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.
- 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.
- 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:
- Plug the primary input of the hot-swap PDU into an on-line UPS system.
- Plug the secondary input into utility power, i.e. a wall outlet.
- 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.
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.
Why Buy from Tripp Lite?
We know you have many brands to choose from. On the surface, they may all seem alike. It's what you don't see that makes the difference. With Tripp Lite, you get solid engineering, proven reliability and exceptional customer service. All our products undergo rigorous quality control before they are offered for sale, and independent testing agencies verify our products meet or exceed the latest safety and performance standards. Our commitment to quality allows us to back our products with industry-leading warranties and responsive customer service. It's the Tripp Lite difference.