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The Raritan Blog

The Advantages of Metering at the Inlet, Outlet, and Branch Circuits of Rack PDUs

Posted on March 13, 2015 by Michael Bord

Raritan Power Distribution Unit

What are the features that separate Non-Intelligent from Intelligent Rack Power Distribution Units (iPDUs)?  There are literally dozens of them.  But, the single most important feature is metering.  Intelligent metering has become pivotal to data centers' understanding of how much power is being used at the device, rack, row, or facility level.  In turn, that information can helps data centers to become more energy efficient, increase uptime/availability, improve mean time to repair (MTTR), and do a better job at managing existing power capacity.  So, let's explore some of the benefits of intelligent metering at the inlet, outlet, and rack PDU branch circuit level. 

Red Power Distribution Unit

Metering at the Inlet

Metering at the inlet helps users to determine power usage and available capacity at the rack, which in turn, makes it easier to provision equipment. By metering at the inlet-level, users can avoid overloading circuits, and more easily calculate efficien­cy metrics like Power Usage Effectiveness (PUE).

Metering at the Outlet

Like metered inlet PDUs, outlet-metered models help users to determine power usage and available capacity at the rack, which in turn, makes it easier to provision equipment. Most importantly, outlet-level metering allows users to understand power consumption at the device or server-level in order to identify ghost servers, find underutilized servers, and allocate costs to specific business units or customers. It also allows data center managers to compare the efficiencies of IT.

Metering at the Rack PDU Branch Circuit

Metering at the Rack PDU branch circuit provides early warning if a circuit is becoming heavily loaded and runs the risk of tripping. Typically users receive an alert based on a pre-existing threshold that informs them when power demands need to be reduced.   Branch circuit metering is important because it allows users to add new devices to the cabinet or rack without having to worry about tripping the circuit breaker. It is particularly important when dealing with high-power consumption devices such as blade servers, because higher draws create an even greater chance of tripping a breaker and experiencing unplanned downtime.

Circuit Breaker Monitoring in the Rack PDU

Monitoring the circuit breaker allows users to know when and where a circuit breaker trips so that it can quickly be reset.


Click here to learn how eBay, one of the world's largest online commerce sites, uses intelligent PDU metering to slash power costs and increase compute performance.