Transformers in the Data Center

EMC VNX5400 Powered By 120 Volts AC

EMC VNX5400 Powered By 120 Volts AC

At my day job, we recently purchased an EMC VNX5400 SAN disk array for use at a secondary data center.  For any readers who aren’t aware, the VNX5400 is a complex and highly customizable piece of equipment that typically costs tens of thousands of dollars or more.

In an attempt to do proper due diligence, we asked well in advance about the specific power requirements of this system.  And we were told that two pre-existing 120 Volt, 20 Amp circuits were more than sufficient for the purpose.  The array is capable of running on 200 – 240 Volts as well, but those circuits have a higher recurring monthly cost.  We don’t use them unless we need to, and we haven’t needed to yet in this secondary location.

Installation day came.  Our EMC partner for this project – Par 4 Technology Group – arrived to rack, connect, power on and help configure the equipment.  Everything went predictably well as we mounted the equipment, save for a bent corner bracket that required straightening.  We ran into a problem, however, when we went to power on what EMC calls the Disk Processor Enclosure (DPE).  It simply wouldn’t power on.

This VNX5400 is a recently-released model, so the Par 4 team began looking for a power switch that might have been added to the configuration, or any other obvious explanation for what might be going on.  After all, the accompanying Disk Array Enclosures (DAEs) lit up just fine using the same circuits.  Soon it was time to call EMC.

As it turns out, EMC has an internal bulletin – not meant for end customers like us – in which they mention that, “our installation guides incorrectly stated that 100 – 120 Volts AC can be used.”  This DPE requires 200 – 240 V AC.

Now when I hear that we don’t meet the power requirements of an enterprise-class device, my first thought (and my only thought, prior to this experience) is that we need to get the higher-voltage circuits installed.  This would require an electrician, several hundred dollars in installation fees, and hundreds of dollars a month in recurring cost for the extra 200 V circuit(s).  Typically we’d install a pair of circuits for fault tolerance.  In addition to the unanticipated costs, we wouldn’t be able to get the SAN deployed on schedule, and would have to get the EMC partner back out at a later date.

But EMC’s internal bulletin didn’t end with the news of the change in power requirements.  They went on to specify that they’d validated a particular power transformer in their lab and are recommending it to customers for use with certain VNX models like ours on 110 V circuits.

In this particular instance, EMC recommends a Hammond Manufacturing 176G autotransformer, available from Mouser for $181.24 each at the time of this writing, and less in quantity.  I placed an order from Mouser at 4:07 PM that day for a pair of Hammond Manufacturing 176G units with overnight shipping.  Total cost was $406, one time only.  By comparison, a new pair of 200 V circuits in this facility might cost our company between $10,000 and $15,000 for the first year, and every year after that.

Anyone purchasing a step-up transformer should note that the output receptacle may be different than what their current power cord accommodates, so as not to be caught scrambling for adapters at the last minute.  Each 176G has a single NEMA 6-15R receptacle, and we’d need a NEMA 6-15P to IEC C13 cable for each of our connections to the DPE.  We scrambled to accommodate this need too, before discovering that EMC had proactively shipped us two of these cables with the VNX5400 in a separate box.

Now I’m not about to suggest that there’s not a place for 200 – 240 V power in a data center.  I’ve been told by two data center operations guys along the way that they prefer to run their entire facility on 200 – 240 V, as it’s more efficient overall.  But in this particular instance, with a single device requiring the higher voltage, step-up transformers proved to be an inexpensive solution that was suitable for the task.  We got our new EMC VNX5400 SAN up and running on schedule in the two days allotted, using the existing 120 V circuits, with only a minimal additional one-time cost of $406.  I’m sure that our company won’t mind saving the $10,000 – $15,000 a year over what might otherwise be necessary.  And from this perspective, perhaps the lesson on transformers alone was $406 well spent.

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