Thanks for returning for Part Six of Tech Service Today's technical buyer's guide series called Size Matters - Especially When Choosing A Network Rack. This series explains why IT professionals must evaluate every dimension of a cabinet or rack before purchasing one. When a rack or cabinet is chosen based on only one or two dimensions, the result is a cabinet that does not properly accommodate your equipment - a costly error that can be avoided by following our advice.

In the first five segments we delivered tips for calculating your real Internal Height requirements for a new rack or enclosure, and the importance of comparing the height of your building's pathways to the External Height of a cabinet or rack. We then provided simple ways to verify your Internal Width requirements while ensuring it has an External Width capable of accommodating the types of equipment and cables it will house. In our last segment, we distinguished between a cabinet's Internal Depth and its Maximum Rail Depth, and explained the importance of assessing both measurements before choosing a cabinet.

Today we will explore the best practices for choosing a rack-mount enclosure with an External Depth that is guaranteed to meet your needs.

Part 6 - External Depth

While determining the best External Depth of a rack-mount enclosure may seem like a no-brainer, there are actually several factors to be considered before you select a cabinet. These include identifying how much extra space you need inside and outside the cabinet.

Let's start with the space surrounding the cabinet, meaning the physical environment where you plan on storing the cabinet.  If you are adding one new cabinet to a row of others in a data center, then matching the external depth of the new cabinet to the existing ones may be your only concern. But if the new cabinet will be placed in a smaller space - like a Telecom closet, IDF, or a site manager's office - then several other factors come into play.

Obviously there is more at stake than whether or not the cabinet will fit into its intended space. The room must also offer adequate space around the cabinet so that the front and rear doors can be opened. Additionally, there must be enough room for a human being to not only fit in the room with the cabinet, but also mount the equipment and cabling inside, and perform moves/adds/ changes and troubleshooting when necessary.

That extra space outside the cabinet is also necessary to permit sufficient air flow so high-speed switches and servers will not overheat. If you decide to store a cabinet in a small closet, make sure the room either has its own, dedicated HVAC system (temperature controls) or portable cooling device like Tripp-Lite's SmartRack Portable Server Rack Cooling Unit. 

Just remember that the best internal equipment cooling fans in the world will not save your servers from frying if you push your cabinet against a wall, thereby preventing the hot air from escaping out the back door. Make sure the room or closet you have chosen to house your new cabinet has ample space outside of the cabinet for both human access and air flow. 

The second consideration when evaluating the External Depth of a new cabinet has nothing to do with the area outside the cabinet, but rather how much extra space you have inside. You are probably asking yourself "isn't that extra space inside a cabinet part of the internal depth?" In short, it is. But savvy IT professionals need to know exactly how much extra depth a cabinet offers behind the rear mounting rails because that is the ideal place to mount vertical cable managers and PDUs. This extra depth can be calculated pretty accurately by subtracting the maximum rail depth from the external depth of the cabinet.

The practice of using zero U vertical cable managers and PDUs inside the back of cabinets is common because it frees up valuable space on the mounting rails for equipment and servers while also keeping all the cables off to the sides where they won't get tangled (a condition that frequently results in accidental disconnects), and they will not obstruct access to the face of equipment and/or airflow. So the depth of a cabinet is often dictated by how many users/cables your network has, and whether or not you plan to use large-channel vertical cable managers and/or vertical PDUs. As the number of cables and cable managers goes up, so should the depth of your cabinet. 

Keep in mind that several cabinet and rack manufacturers are now offering 48-inch deep rack-mount enclosures to provide the extra depth that IT professionals require in high density environments.  Since the maximum rail depth of those cabinets are typically 40-inches or less, they provide ample space behind the rear rails to keep even the most cable-intensive networks organized and out of the way of your equipment.

Tech Tip #6 - External Depth

Here are today's tips for determining the ideal External Depth of a cabinet.

- The cabinet you choose for placement in a small space (like closet or IDF) must have an external depth that will fit in its designated space while still allowing enough room for the free, unobstructed opening and closing of the front and rear doors.

- The external depth of a cabinet must not be so deep that it prevents a person from moving around all side of it and/or accessing, installing, and removing equipment through the front and back doors.

- Choose a cabinet whose external depth is at least 4"-6" deeper than the deepest piece of equipment you plan to mount so that cables connected to equipment will neither be forced to exceed their allowable bend radius nor obstruct proper closure of the front and rear doors. And if you plan to mount vertical PDUs or large-channel vertical cable managers behind the rear rails, make sure the cabinet has the depth needed to accommodate those once the rails have been set to their desired depth.

Return tomorrow for our seventh segment in this series, focusing on the Cabinet Door Types and tips for choosing the right ones on your cabinet.

Are you planning an IT rollout project involving the installation of new hardware and/or racks to multiple sites?  Then download a free copy of TST's Best Practices for IT Rollout Projects.   

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