Servertech: Ask the Engineer – How much power should I provision for my cabinets?

This is a common question I receive: How much power should I provision for my cabinets?

This can be a very complex question depending upon your goals for today and plans for the future. At the top end, you might provision enough power per cabinet to fully utilize your cooling capacity. For instance, if you can cool 500kW and have 100 cabinets, then you can provide 5kW to each cabinet. This is usually too simplistic because you may have certain high-density cabinets. But, the intent of this post isn’t to cover all of the infrastructure concerns. It is simply to focus at the cabinet level.

You need to start with the question of how much do you need today? You must, of course, identify all of the equipment you intend to put into each cabinet. The trick is then to determine how much power each piece of equipment will draw, that is, what amperage and at what voltage input. Also, if you can get the value of the power factor for the equipment supplies, you will get a better answer. There are various methods to figure the equipment draw.

Method 1: The simplest way is to assume a worst case in which the equipment will draw the maximum that the power supply can handle. This is the “name-plate rating”. For instance, the Dell PowerEdge R900 is supplied with hot-swappable 1570W (180V-240V) 90% efficient power supplies. One thing to note here is that the 1570W rating is the maximum output of the supply. You must divide by 0.9 (the efficiency) to find the maximum draw. So the R900 could draw 1745W using this method.

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Alex Carroll

Managing Member at Lifeline Data Centers

Alex, co-owner, is responsible for all real estate, construction and mission critical facilities: hardened buildings, power systems, cooling systems, fire suppression, and environmentals. Alex also manages relationships with the telecommunications providers and has an extensive background in IT infrastructure support, database administration and software design and development. Alex architected Lifeline’s proprietary GRCA system and is hands-on every day in the data center.