ServerTech Blog - Information for the Data Center Equipment Manager

Ask the Engineer - At what amperage does a 20-amp fuse blow?

Question from Antonio Esparza: At what amperage does a 20-amp fuse blow? Is it exactly at 20 amps or is there a variance?

Engineer Reply: STI Cabinet PDU's utilize Bussmann SC-20G fuses to protect the outlets at 20 amps. Fuses don't have a fixed point for tripping, though they are consistent from one fuse to the next. So, don't think of it as a variance. The 20A rating does not actually mean that it will trip at 20A like flipping a switch. Fuses are resistive devices that get hot with current flowing through them. They can only withstand so much heat, so the higher the current flowing, the faster they blow. The chart on page three of the spec shows the tripping time for any particular current. For instance, 30A will take roughly 100 seconds, 73A will take roughly 1 second, and 120A will take roughly 0.1 second. Keep in mind that a short circuit fault is going to attempt to draw thousands of amps, so tripping will be much faster. Indeed, one of the benefits of using fuses over circuit breakers is the reaction being as much as 5x faster for a short circuit fault.

Ask the Engineer - Does upgrading Cabinet PDU firmware affect outlet power?

Question from Kerri Bruce: I'd like to upgrade some Sentry PDU's to version 6.0g to implement RADIUS. Does that cause outlets to reboot?

Engineer Reply: Server Technology intelligent Cabinet PDU's have embedded firmware that is flash upgradeable through FTP download. Updating firmware does NOT require any interruption in power to attached devices. All PDU firmware updates are available for free through the Server Technology website. Simply navigate through the directory structure to find the file for upgrade. Note that the "Auto Update" directory houses only the newest firmware version for each product family. Also note that free FTP server software is available there as well.

With your FTP server running and the binary update file in a set location, the Cabinet PDU's must be set to upgrade themselves. Log into a PDU, click "Configuration" in the left menu, click "FTP", and enter information into the fields for Host, Username, Password, Directory, and Filename. Click the "Test" button and wait for verification of success. Click the "Apply" button. Also note that the PDU can be set to automatically look for updates on your FTP server. Also note that the PDU can be used as an FTP server for upload/download of certain configuration files including ftp.ini which allows you to get the FTP settings from one Cabinet PDU and put them into all others in your network.

To initiate the firmware update, click "Tools" in the left menu, click "Restart", from the drop-down box select "Restart and upload firmware via FTP", click the "Apply" button, and confirm the command in the pop-up window. Communication will be lost to the PDU during the upgrade process; however, power at the outlets will not be affected.

Ask the Engineer - Linking feature explained

Question from Anouk Vander Heiden: Can I daisy chain multiple Cabinet PDU's to use just one network port?

Engineer Reply: STI Smart and Switched PDU's can be setup in a Master-Expansion configuration for use as a single cabinet solution to provide power redundancy under a single IP address. Daisy chaining beyond that cannot be done with STI Cabinet PDU's. Although it can be beneficial to reduce IP addresses, daisy chaining creates a situation where a network fault at one PDU would bring down communication to many others.

STI's linking technology allows any Master Smart (CS) series PDU to link to any Expansion Smart (CL) series Cabinet PDU regardless of outlet count or input connection. Or, any Master Switched (CW, PTXL, XLS) series PDU or RPM to link to any Expansion Switched (CX, PTXM, XMS) series PDU or RPM. This includes the ability to link AC units with DC units for single point network and out-of-band access.

The ability to link together two Cabinet PDU's with independent power input feeds gives one the ability to see all outlets within a cabinet under one graphical interface. And, by using the outlet grouping feature of the embedded interface, one can reboot a device with redundant power supplies using a single command.

Datacentre Strategics - Sydney, Australia on August 14th

Server Technology will be taking part in the Datacentre Strategics show in Sydney, Australia on August 14th at the Hilton Sydney.

Register now for the show!

Data Center topics that will be addressed by speakers from the Data Center Industry include:

• Data Centre Design Best Practice
• Disaster Recovery; Directions, Impact & Resilience
• Integration of IT and Facilities
• Rack level power distribution units (PDUs) for improving uptime, capacity planning and efficiency
• Controlling temperature in High Density Data Centers
• Panel discussions on Power & Cooling, Communications & Networking and Planning & Design

Server Technology will have representatives available to listen to your Data Center goals and plans regarding power and power distribution needs.

Understanding The Green Grid's PUE and DCiE metrics

The Green Grid recently held their Next Generation Data Center (NGDC) online summit featuring IT experts from throughout the industry. Below is a link to a presentation that provides an excellent overview of TGG's PUE and DCiE power metrics and how to report these figures. Additionally, they provide a glimpse of a new metric they are working on, DCP (Data Center Productivity), which is Useful Work divided by the Total Facility Power.

The Green Grid and the Future of the Data Center

Ask the Engineer - De-rating explained.

Question from Sean Howard: I have your power strips with ratings of 16A stated on the side label. Do I have to de-rate from that down to 12.8 amps?

Engineer Reply: No, you don't Sean. There are some ambiguous terms used for ratings. As you point out, it is common to use the term "de-rate" using the 80% rule in North America due to the NEC requirements. So, a "20-amp" CDU is "de-rated" to 16 amps. The requirement is that the label state the continuous usage rating, thus we can say that the "continuous usage rating" is the same as the "de-rating". The NEC actually treats the ratings in the opposite manner by using "continuous" and "maximum" ratings such that the maximum rating is 125% of the continuous rating. So, a 16-amp continuous rated CDU has a maximum rating of 20 amps. Additionally, you should be aware that usage can go as high as the maximum rating for short periods of time - "continuous" is defined as longer than 3 hours.

Sizing Up Your Data Center Power Requirements

Capacity planning can be tricky given all the factors that come into play. In order to size the UPS and cooling requirements, the power load of all the IT equipment must first be determined. The nameplate ratings found on the equipment are notoriously high because these power supplies are rated while running at 100% and are typically designed to work with other products or future generations of a device. Some equipment manufacturers provide power calculators for various configurations of their products. A more accurate method is to trend the load by monitoring outlet-level power utilization over time and at various degrees of utilization. This information can be used to extrapolate future requirements for both the near term and future growth three to four years down the road. A recent article in SeachDataCenter.com covers these and other issues to consider.

Other factors to consider are where opportunities exist to increase power efficiency such as the advantages of using 208V, 3-phase power or possibly deploying 240V/415V. Server Technology has published three white papers covering these topics:

• Measuring Power and Efficiency
• Planning, Implementing and Application of Cabinet Power Distribution Units
• Power Efficiency Gains by Deploying 415 VAC Power Distribution in North American Data Centers