What's so great about the Metered PDUs
Posted by Jim Scherr on Tue, Dec 29, 2009
So you are looking for power distribution for your server racks. The basic PDUs are easy and inexpensive; the switched units are more than you need, but what about the Metered PDUs.
Metered rack PDUs have an LED display on the front of the unit that shows the amps being drawn by the circuit. That's kind of cool to have, but what do you do with it? The meter serves a number of purposes from the initial installation to adding additional equipment, but the key reason for the metered power distribution unit is to prevent a circuit overload that will take down your equipment.
As you initially load servers, network devices, or other equipment use the meter to ensure you are drawing less than the circuit maximum. For a 20A circuit the UL derated standard is 16A, and for a 30A circuit it is 24A. Remember the initial load is at idle so it will probably increase as your operations ramp up. Also, if you planned your layout based on device specs, realize the specs are written to maximums. The normal usage will probably be 30-40% less. If you operate from a co-location facility and you pay a monthly fee for each circuit, maximizing your circuits can save you a significant amount of money
For critical equipment, power redundancy is a widely used best practice. For power redundancy, a minimum of two power circuits are supplied to each cabinet, and multiple power supply equipment is used. The intention is that in the event of a lost circuit, due to a short or bad device power supply, the remaining circuit would be able to pick up the load and keep the equipment running. To work each circuit can be loaded no more than half the circuit maximum. Again, for a 20A circuit (derated to 16A), the maximum load would be 8A. Here the meter is extremely useful both in the initial build out and monitoring ongoing operations.
Many facilities teams also perform periodic audits of power consumption. I had a large TV network customer that audited the power draw of each rack twice a year. Before they moved to metered PDUs they spent three days measuring over 400 racks with a clamp meter. Using the metered PDUs they were able to complete the audit in half a day.
The metered power distribution units can also assist IT manager with planning out expansions. Not only do they give you an accurate depiction of what your current rack configurations consume, but they also help you identify racks that have capacity to add additional equipment. This can save you from needing to purchase additional infrastructure, like racks, UPSs, power circuits, and PDUs.
These are just a few of the uses for the local power LED meters. I am constantly impressed with the new and innovative ways our customers use our products. If you have any other uses you've found, please let us know.