For a typical domestic electrical consumer with more than one device powered from a standard electrical outlet a normal power strip is usually enough to meet their demands. Power strips can be said to be the most basic form of a PDU. They are electrical devices that receive AC/DC power from a given source and reliably redistribute it as either AC/DC out of the various standard electrical outlets. The source of this power can be a generator, an uninterruptible power supply (UPS) or from the power grid. The UPS in most cases is connected to a string of back up batteries charged by the mains supply or solar.

On the other hand, Telecom, Data-com and Internet Service Providers may not necessarily find power strips sufficient for their operations. This is because they operate within a space where they are frequently required to scale up their systems (adding and replacing units) while needing some means of remote management of their power devices.

However, this does not mean that a typical residential house would not find need for the PDUs.

An intelligent Power Distribution Unit (PDU) fills the gaps that the typical power strip cannot. It provides a central unit to control and distribute electricity across the different connected devices.

What then is an intelligent PDU?

This is a device which provides unfiltered electrical pass-through power through its outlet receptacles with added monitoring, management and control features either locally or remotely via the network. Note that a PDU does not generate neither does it condition power to the outlets, what it does is provide the power as it receives it.
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Fig1: Typical PDU setup

What key considerations should you look at when selecting a PDU?

1. Type of PDU
Within the market there are several PDUs that are easily available. The consumer needs to understand which one best suits their needs and which one would offer them the reliability of service required. Based on their different functionalities PDUs can be broadly classified as:
  • Metered
They provide localized real-time load monitoring via current sensors on the outlets to give the amperage. These readings are displayed on an LCD monitor built into the PDU. This helps avoid potential overloads.
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  • Monitored
In addition to providing a localized means of monitoring power outputs they come with different network interfaces (RJ45/Serial/WiFi) for SNMP protocols. This allows the readings to be visualized remotely via the network. They come with a firmware specific to the product to support these functionalities.
  • Switched
These provide an ability to monitor the PDU parameters locally via an LCD display and remotely via the serial interface or other network interfaces while bringing in the capability to remotely control the outlets. This implies you can remotely switch the outlets on and off to reboot connected devices or vary other parameters like current/voltage.
They also come with a manufacturer specific firmware to support these functionalities.
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They can be additionally classified as:
  • Switched Metered-by-Outlet
They allow you to individually monitor and remotely control your outlets for more efficient energy usage. All these are done in real time either remotely via the network or locally using the onboard LCD display. This implies you can remotely switch the outlets on and off to reboot, power cycle and perform load shedding on the connected devices. Some manufacturers have added features like power event notifications via email and SMS text.
They also come with a manufacturer specific firmware to support these functionalities.
  • Metered Auto Transfer Switch (ATS)
These are inherently metered PDUs providing localized monitoring of parameters via the LCD display. The added functionality is that they have redundant input power plugs such that your devices can be supplied from two or more different power sources. They distribute the power unfiltered to the outlets. When the input power from the primary source exceeds or falls below the requirements of the connected device the PDU automatically switches to the secondary sources till the primary stabilizes. You then have continuous operation of your critical network equipment.
  • Switched Auto Transfer Switch (ATS)
These are switched PDUs providing remote and localized control of the outlets either as a single outlet or as a group. The added functionality is that they have redundant input power plugs such that your devices can be supplied from two or more different power sources. They distribute the power unfiltered to the outlets. When the input power from the primary source exceeds or falls below the requirements of the connected device the PDU automatically switches to the secondary sources till the primary stabilizes. This guarantees continuous operation of connected device and avoids device damage.
  • Maintenance Bypass/ Hot-Swap
They are designed for operations where devices must not go down or be interrupted. These are primarily key network components whose uptime must be maintained. The Maintenance Bypass PDU allows for the seamless transfer of power from the utility supply to a secondary supply like a UPS or Battery strings.

2. Form factor and Nature of installation
Typically, the PDUs come in 0U, 1U and 2U sizes for mounting on rack units. The 1U and 2U are horizontal mount on 19-inch racks while the 0U is a vertical mount. The 0U installation allows you to reserve critical space for the other network components that require horizontal mounting. The 1U & 2U installations allow you to locate the PDU as close as possible to the powered device by placing it above, below or in between the connected devices. Using the associated mounting brackets and different screws the PDUs can also be mounted on a wall or any other safe, stable and flat surface.
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Fig. 2: Typical PDU Orientations

Other PDUs are also quite mobile and need not be mounted, requiring only to be placed on a stable and flat surface like the LPC9 from Digital Loggers. With these types you need to be able to properly manage your power cables to avoid safety mishaps. Consequently, to establish what PDU you need you must know where and how you will install it to settle on which one best meets your demands.

3. Available Input Power & Expected Output Power
Depending on geographical or physical location you may have access to different types of power. The power could be from a solar installation, utility supply, UPS or battery backup etc. It could be AC or DC; AC single-phase or three-phase and it could have any input ranging from close to 0V to over 300V at different power ratings. Primarily, most homes, offices and general communication equipment use single phase AC power. Three phase power is reserved for heavy industrial equipment which have more advanced power supply systems and PDUs.

It is critical to note that for input AC power most PDUs can automatically switch from 120V to 240V as per the available supply voltage. For DC, the PDUs can also accept a range of input VDC as per the device circuit ratings. The power supply demands must therefore be arrived at using the specific input voltage to be used.

At the output, all connected network devices will come with clearly indicated input power ratings given in either Watts(W) or Volt-Amperes (VA). To get the output total, sum the ratings for all devices that will be connected. The PDU you settle on must therefore be able to efficiently use the available power and its power rating exceed that of all connected devices.

4. Number of Outlets & Nature of Electrical outlets
The number of available outlets must be equal to if not greater than the number of devices to be connected. Having more outlets than devices gives room for future expansion and creates redundancy such that in case one or more outlets fail you only need to switch the output cable to another port and continue operation.

The nature of outlet implies the standard in use, whether NEMA or IEC. Each standard outlet has a distinct shape for its connector/plug and a specific power rating which should not be exceeded as highlighted here.

Why should you get an Intelligent PDU?
  • Better control of your power – They offer ability to monitor your power at the outlet level thus provide a good analysis of your power consumption. This will allow you to better scale up your systems and plan for future growth.
  • The availability of sensors (temperature, humidity, airflow, air pressure, water leaks, proximity, vibration, and contact closure) allows you to monitor your operating environment and optimize equipment operation for longer service. These sensors will alert the system to send alarms when certain minimum or maximum thresholds are exceeded.
  • Ability to remotely reboot, power-cycle and perform load shedding – They allow for remote control of individual or multiple outlets. You don’t have to be physically at the location center but only send commands via the network to control the PDUs.
For your customized power solution contact an Rfwel Power Monitor & Control Specialist. Find us also on +1 480 218 1877.
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