This article is the first in a new mini-series where I will be doing semi-deep dives on some of the simpler, but often overlooked, aspects of network and datacenter engineering.
Approx Reading Time: 3-4 Minutes
It is quite commonplace these days to see equipment mounted incorrectly in a rack. Even though we are not mechanical engineers, it is beneficial to understand the principles behind the parts of our jobs ruled by mechanics. Let’s review a little of the science behind mounting equipment in a 2-post rack.
The Short Version
The Long Version
The lever is a simple machine, consisting of a beam and a fulcrum which converts the ratio of input force to output force. In short, a lever allows you to convert a small amount of force over a large distance into a large amount of force over a small distance (or vice-versa).
This allows you to move something very heavy (or very secure) using a small amount of effort over a large distance.
Why Does This Matter?!?!?!
A 2nd class lever is where the load is in-between the fulcrum and the point of effort. A switch mounted in a rack is essentially a 2nd class lever with a 90 degree bend in the “beam”. The force (or effort) is being applied to the body of the switch (behind the rails) by gravity. The fulcrum is the highest place on the switch in contact with the rack rails. The “load” is the force being applied on the bottommost point of the switch, which is fastened to the rails (likely by the lowest screw).
The goal when mounting a switch in a rack is to reduce the load on the bottommost screw as much as possible. This is done by putting the maximum amount of space between the fulcrum (topmost point where the switch touches the rails) and the load (the bottommost screw).
When a switch is mounted using screws in only the top holes of the ears, it creates a very small space between the fulcrum and the load; which usually results in a sagging switch and bent ears. This is why it is recommended to always secure a switch to a rack using the lowest available holes in the rack ears.
Remember this principle next time you rack a switch and are faced with the decision of how to get it done!