When space for rack mount equipment is at a premium, there’s usually one direction to go: up. That’s why it can be tempting to look for the tallest possible rack mount case. Here’s why that might not be a good idea.
Case Height Specifications
Rack mount cases are specified in terms of U numbers, short for RU or “Rack Unit”. One U is 1.75 inches. A 10U case provides 17.5 inches of vertical height for mounting electric equipment. Rack mount transit cases go as tall as 31U, which is about 54.25 inches. That’s just the available interior space. Outside, the case will be significantly larger.
As a case gets taller, it’s more prone to tipping. That’s not an issue for equipment going into a server room. But, when it has to be moved – perhaps over rough terrain – a wide, low case is preferable.
Despite the designer’s best efforts, transit cases for rack mount equipment have appreciable mass. A 15U case can easily weigh over 80 lbs. – before the payload is secured inside. That’s a problem. Sooner or later someone is going to need to lift it.
Lifting overly heavy loads causes back injuries. The MIL-STD-1472G standard, which addresses human factors in military equipment design, sets limits on how much a person can lift.
These limits relate to how high a load is to be raised and the gender of the person doing the lifting. For a man, the recommended floor to bench height limit is 87 lbs. (39.5 kg.). If the load is to be raised higher, the limits fall. The limit is reduced if the lifting is to be repeated frequently, if there’s twisting involved, and if the depth of the load (the distance away from the lifter) exceeds 12 inches. For women, all limits are lower.
This means, an empty 15U case comes close to the limit of what a fit young male should lift. Now, fill it with equipment, moving it takes two men.
Choosing Your Case
Rack mount transit cases are available in sizes as big as 31U. But when they get taller than 16U, it’s prudent to ask about a custom case. Alternatively, lifting rings, heavy-duty casters and fork lift skids should be considered.
If possible, try to split the payload into two smaller cases. For example, consider two 10U cases rather than one 20U case. That’s usually better than going with one tall rack mount case.
See our selection of Rack Mount Transit Cases.